ATMEGA164P-B_14 [ATMEL]
8-bit Atmel Microcontroller with 16/32/64Kbytes In-system Programmable Flash;
| 型号： | ATMEGA164P-B_14 |
| 厂家： | 
ATMEL |
| 描述： | 8-bit Atmel Microcontroller with 16/32/64Kbytes In-system Programmable Flash 微控制器 |
| 文件： | 总344页 (文件大小：11608K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
ATmega164P-B/ATmega324P-B/
ATmega644P-B Automotive
8-bit Atmel Microcontroller with 16/32/64Kbytes
In-system Programmable Flash
DATASHEET
Features
● High-performance, low-power Atmel® AVR® 8-bit microcontroller
● Advanced RISC architecture
● 131 powerful instructions – most single-clock cycle execution
● 32 × 8 general purpose working registers
● Fully static operation
● Up to 16MIPS throughput at 16MHz
● On-chip 2-cycle multiplier
● High endurance non-volatile memory segments
● 16/32/64Kbytes of in-system self-programmable flash program memory
● 512/1/2Kbytes EEPROM
● 1/2/4Kbytes internal SRAM
● Write/erase cycles: 10,000 flash/ 100,000 EEPROM
● Data retention: 20 years at 85°C/ 100 years at 25°C(1)
● Optional boot code section with independent lock bits
● In-system programming by on-chip boot program
● True read-while-write operation
● Programming lock for software security
● QTouch® library support
● Capacitive touch buttons, sliders and wheels
● QTouch and QMatrix acquisition
● Up to 64 sense channels
● JTAG (IEEE std. 1149.1 compliant) interface
● Boundary-scan capabilities according to the JTAG standard
● Extensive on-chip debug support
● Programming of flash, EEPROM, fuses, and lock bits through the JTAG
interface (1)
● Peripheral features
● Two 8-bit Timer/Counters with separate prescalers and compare modes
● One/two 16-bit Timer/Counter with separate prescaler, compare mode, and
capture mode
● Real time counter with separate oscillator
1. See Section 5. “Data Retention” on page 8 for details.
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● Six PWM channels
● 8-channel, 10-bit ADC
● Differential mode with selectable gain at 1x, 10x or 200x
● Byte-oriented two-wire serial interface
● Two programmable serial USART
● Master/slave SPI serial interface
● Programmable watchdog timer with separate on-chip oscillator
● On-chip analog comparator
● Interrupt and wake-up on pin change
● Special microcontroller features
● Power-on reset and programmable brown-out detection
● Internal calibrated RC oscillator
● External and internal interrupt sources
● Six sleep modes: Idle, ADC noise reduction, power-save, power-down, standby and extended standby
● I/O and packages
● 32 programmable I/O lines
● 44-lead TQFP, 44-pad QFN/MLF
● Operating voltages
● 2.7 to 5.5V
● Speed grades
● 0 to 8MHz at 2.7 to 5.5V; 0 to 16MHz at 4.5 to 5.5V
● Power consumption at 8MHz, 2.7V, 25°C
● Active: 4.8mA
● Idle mode: 1mA
● Power-down mode: 0.6µA
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1.
Pin Configurations
1.1
Pinout - TQFP/QFN/MLF for ATmega164P-B/324P-B/644P-B
Figure 1-1. Pinout
44 43 42 41 40 39 38 37 36 35 34
(PCINT13/CP3/MOSI) PB5
(PCINT14/OC3A/MISO) PB6
(PCINT15/OC3B/SCK) PB7
RESET
1
33
32
31
30
29
28
27
26
25
24
23
PA4 (ADC4/PCINT4)
PA5 (ADC5/PCINT5)
PA6 (ADC6/PCINT6)
PA7 (ADC7/PCINT7)
AREF
2
3
4
VCC
GND
XTAL2
XTAL1
5
6
TQFP/QFN/MLF
GND
AVCC
7
8
PC7 (TOSC2/PCINT23)
PC6 (TOSC1/PCINT22)
PC5 (TDI/PCINT21)
PC4 (TDO/PCINT20)
(PCINT24/RXD0/T3) PD0
(PCINT25/TXD0) PD1
(PCINT26/RXD1/INT0) PD2
9
10
11
12 13 14 15 16 17 18 19 20 21 22
Note:
The large center pad underneath the QFN/MLF package should be soldered to ground on the board to ensure
good mechanical stability.
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2.
Overview
The ATmega164P-B/324P-B/644P-B is a low-power CMOS 8-bit microcontroller based on the AVR® enhanced RISC
architecture. By executing powerful instructions in a single clock cycle, the ATmega164P-B/324P-B/644P-B achieves
throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing
speed.
2.1
Block Diagram
Figure 2-1. Block Diagram
PA7 to 0
PB7 to 0
PA7 to 0
Power
Supervision
POR/ BOD
and RESET
RESET
PORT A (8)
PORT B (8)
GND
Watchdog
Timer
A/D
Converter
Analog
Comparator
USART 0
Watchdog
Oscillator
XTAL1
Internal
Bandgap reference
EEPROM
SPI
Oscillator
Circuits/
Clock
Generation
8 bit T/C 0
16 bit T/C 1
8 bit T/C 2
16 bit T/C 3
XTAL2
AVR CPU
JTAG/OCD
TWI
USART 1
FLASH
SRAM
PORT C (8)
PORT D (8)
TOSC2/PC7 TOSC1/PC6
PC5 to 0
PD7 to 0
The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are directly
connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction
executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times
faster than conventional CISC microcontrollers.
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The ATmega164P-B/324P-B/644P-B provide the following features:
16/32/64Kbytes of in-system programmable flash with read-while-write capabilities, 512/1/2Kbytes EEPROM, 1/2/4Kbytes
SRAM, 32 general purpose I/O lines, 32 general purpose working registers, real time counter (RTC), three flexible
Timer/Counters with compare modes and PWM, 2 USARTs, a byte oriented 2-wire serial interface, a 8-channel, 10-bit ADC
with optional differential input stage with programmable gain, programmable watchdog timer with internal oscillator, an SPI
serial port, IEEE std. 1149.1 compliant JTAG test interface, also used for accessing the on-chip debug system and
programming and six software selectable power saving modes. The idle mode stops the CPU while allowing the SRAM,
Timer/Counters, SPI port, and interrupt system to continue functioning. The power-down mode saves the register contents
but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset. In power-save mode, the
asynchronous timer continues to run, allowing the user to maintain a timer base while the rest of the device is sleeping. The
ADC noise reduction mode stops the CPU and all I/O modules except asynchronous timer and ADC, to minimize switching
noise during ADC conversions. In standby mode, the crystal/resonator oscillator is running while the rest of the device is
sleeping. This allows very fast start-up combined with low power consumption. In extended standby mode, both the main
oscillator and the asynchronous timer continue to run.
Atmel® offers the QTouch® library for embedding capacitive touch buttons, sliders and wheels functionality into AVR
microcontrollers. The patented charge-transfer signal acquisition offers robust sensing and includes fully debounced
reporting of touch keys and includes Adjacent Key Suppression® (AKS®) technology for unambiguous detection of key
events. The easy-to-use QTouch Suite toolchain allows you to explore, develop and debug your own touch applications.
The device is manufactured using Atmel’s high-density nonvolatile memory technology. The on-chip ISP flash allows the
program memory to be reprogrammed in-system through an SPI serial interface, by a conventional nonvolatile memory
programmer, or by an on-chip boot program running on the AVR core. The boot program can use any interface to download
the application program in the application flash memory. Software in the boot flash section will continue to run while the
application flash section is updated, providing true read-while-write operation. By combining an 8-bit RISC CPU with
in-system self-programmable flash on a monolithic chip, the Atmel ATmega164P-B/324P-B/644P-B is a powerful
microcontroller that provides a highly flexible and cost effective solution to many embedded control applications.
The ATmega164P-B/324P-B/644P-B is supported with a full suite of program and system development tools including:
C compilers, macro assemblers, program debugger/simulators, in-circuit emulators, and evaluation kits.
2.2
Automotive Quality Grade
The ATmega164P-B/324P-B/644P-B have been developed and manufactured according to the most stringent requirements
of the international standard ISO-TS-16949. This data sheet contains limit values extracted from the results of extensive
characterization (temperature and voltage).
The quality and reliability of theATmega164P-B/324P-B/644P-B have been verified during regular product qualification as
per AEC-Q100 grade 1.
As indicated in the ordering information paragraph, the products are available in only one temperature grade.
Table 2-1. Temperature Grade Identification for Automotive Products
Temperature
Temperature Identifier Comments
Full automotive temperature range
–40; +125°C
Z
2.3
Comparison Between ATmega164P-B, ATmega324P-B and ATmega644P-B
Table 2-2. Differences between ATmega164P-B, ATmega324P-B and ATmega644P-B
Device
Flash
16K
EEPROM
512
RAM
1K
Unit
ATmega164P-B
ATmega324P-B
ATmega644P-B
32K
1K
2K
Bytes
64K
2K
4K
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2.4
Pin Descriptions
2.4.1 VCC
Digital supply voltage.
2.4.2 GND
Ground.
2.4.3 Port A (PA7:PA0)
Port A serves as analog inputs to the analog-to-digital converter.
Port A also serves as an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port A output
buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port A pins that are
externally pulled low will source current if the pull-up resistors are activated. The Port A pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port A also serves the functions of various special features of the ATmega164P-B/324P-B/644P-B as listed in Section 14.3.1
“Alternate Functions of Port A” on page 63.
2.4.4 Port B (PB7:PB0)
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, Port B pins that are externally pulled
low will source current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Port B also serves the functions of various special features of the ATmega164P-B/324P-B/644P-B as listed in Section 14.3.2
“Alternate Functions of Port B” on page 65.
2.4.5 Port C (PC7:PC0)
Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port C output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, Port C pins that are externally pulled
low will source current if the pull-up resistors are activated. The Port C pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Port C also serves the functions of the JTAG interface, along with special features of the ATmega164P-B/324P-B/644P-B as
listed in Section 14.3.3 “Alternate Functions of Port C” on page 68.
2.4.6 Port D (PD7:PD0)
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port D output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, Port D pins that are externally pulled
low will source current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Port D also serves the functions of various special features of the ATmega164P-B/324P-B/644P-B as listed in Section 14.3.4
“Alternate Functions of Port D” on page 70.
2.4.7 RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not
running. The minimum pulse length is given in Section 28.5 “System and Reset Characteristics” on page 291. Shorter pulses
are not guaranteed to generate a reset.
2.4.8 XTAL1
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
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2.4.9 XTAL2
Output from the inverting Oscillator amplifier.
2.4.10 AVCC
AVCC is the supply voltage pin for Port A and the Analog-to-digital Converter. It should be externally connected to VCC, even
if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.
2.4.11 AREF
This is the analog reference pin for the analog-to-digital converter.
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3.
4.
Resources
A comprehensive set of development tools, application notes and datasheetsare available for download on
http://www.atmel.com/avr
About Code Examples
This documentation contains simple code examples that briefly show how to use various parts of the device. Be aware that
not all C compiler vendors include bit definitions in the header files and interrupt handling in C is compiler dependent. Please
confirm with the C compiler documentation for more details.
The code examples assume that the part specific header file is included before compilation. For I/O registers located in
extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with instructions that allow
access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
Note:
1.
5.
6.
Data Retention
Reliability Qualification results show that the projected data retention failure rate is much less than 1 PPM over 20 years at
85°C or 100 years at 25°C.
Capacitive Touch Sensing
The Atmel QTouch library provides a simple to use solution to realize touch sensitive interfaces on most Atmel AVR
microcontrollers. The QTouch library includes support for the QTouch and QMatrix acquisition methods.
Touch sensing can be added to any application by linking the appropriate Atmel QTouch Library for the AVR Microcontroller.
This is done by using a simple set of APIs to define the touch channels and sensors, and then calling the touch sensing
API’s to retrieve the channel information and determine the touch sensor states.
The QTouch Library is FREE and downloadable from the Atmel website at the following location:
http://www.atmel.com/qtouchlibrary
For implementation details and other information, refer to the Atmel QTouch Library User Guide - also available for download
from the Atmel website.
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7.
AVR CPU Core
7.1
Overview
This section discusses the AVR® core architecture in general. The main function of the CPU core is to ensure correct
program execution. The CPU must therefore be able to access memories, perform calculations, control peripherals, and
handle interrupts.
Figure 7-1. Block Diagram of the AVR Architecture
Data Bus 8-bit
Program
Counter
Status and
Control
Flash
Program
Memory
Interrupt
Unit
32 x 8
General
Purpose
Registers
Instruction
Register
SPI
Unit
Instruction
Decoder
Watchdog
Timer
ALU
Analog
Comparator
Control Lines
I/O Module 1
I/O Module 2
I/O Module n
Data
SRAM
EEPROM
I/O Lines
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with separate memories and
buses for program and data. Instructions in the program memory are executed with a single level pipelining. While one
instruction is being executed, the next instruction is pre-fetched from the program memory. This concept enables instructions
to be executed in every clock cycle. The program memory is in-system reprogrammable flash memory.
The fast-access register file contains 32 x 8-bit general purpose working registers with a single clock cycle access time. This
allows single-cycle arithmetic logic unit (ALU) operation. In a typical ALU operation, two operands are output from the
register file, the operation is executed, and the result is stored back in the register file – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for data space addressing – enabling
efficient address calculations. One of the these address pointers can also be used as an address pointer for look up tables in
flash program memory. These added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register
operations can also be executed in the ALU. After an arithmetic operation, the status register is updated to reflect
information about the result of the operation.
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Program flow is provided by conditional and unconditional jump and call instructions, able to directly address the whole
address space. Most AVR instructions have a single 16-bit word format. Every program memory address contains a 16 or
32-bit instruction.
Program flash memory space is divided in two sections, the boot program section and the application program section. Both
sections have dedicated Lock bits for write and read/write protection. The SPM instruction that writes into the application
flash memory section must reside in the boot program section.
During interrupts and subroutine calls, the return address program counter (PC) is stored on the stack. The stack is
effectively allocated in the general data SRAM, and consequently the stack size is only limited by the total SRAM size and
the usage of the SRAM. All user programs must initialize the SP in the reset routine (before subroutines or interrupts are
executed). The stack pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed through
the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional global interrupt enable bit in the status
register. All interrupts have a separate interrupt vector in the interrupt vector table. The interrupts have priority in accordance
with their interrupt vector position. The lower the Interrupt vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as control registers, SPI, and other I/O functions.
The I/O memory can be accessed directly, or as the data space locations following those of the register File, 0x20 - 0x5F. In
addition, the ATmega164P-B/324P-B/644P-B has extended I/O space from 0x60 - 0xFF in SRAM where only the
ST/STS/STD and LD/LDS/LDD instructions can be used.
7.2
7.3
ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose working registers. Within a
single clock cycle, arithmetic operations between general purpose registers or between a register and an immediate are
executed. The ALU operations are divided into three main categories – arithmetic, logical, and bit-functions. Some
implementations of the architecture also provide a powerful multiplier supporting both signed/unsigned multiplication and
fractional format. See the “Instruction Set” section for a detailed description.
Status Register
The status register contains information about the result of the most recently executed arithmetic instruction. This
information can be used for altering program flow in order to perform conditional operations. Note that the status register is
updated after all ALU operations, as specified in the instruction set reference. This will in many cases remove the need for
using the dedicated compare instructions, resulting in faster and more compact code.
The status register is not automatically stored when entering an interrupt routine and restored when returning from an
interrupt. This must be handled by software.
7.3.1 SREG – Status Register
The AVR Status Register – SREG – is defined as:
Bit
7
I
6
T
5
H
4
S
3
V
2
N
1
Z
0
C
0x3F (0x5F)
Read/Write
Initial Value
SREG
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
• Bit 7 – I: Global Interrupt Enable
The global interrupt enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then
performed in separate control registers. If the global interrupt enable register is cleared, none of the interrupts are enabled
independent of the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is
set by the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by the application with the
SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The bit copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the operated bit. A bit
from a register in the register file can be copied into T by the BST instruction, and a bit in T can be copied into a bit in a
register in the register file by the BLD instruction.
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• Bit 5 – H: Half Carry Flag
The half carry flag H indicates a half carry in some arithmetic operations. Half carry Is useful in BCD arithmetic. See the
“Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N
V
The S-bit is always an exclusive or between the negative flag N and the two’s complement overflow flag V. See the
“Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The two’s complement overflow flag V supports two’s complement arithmetics. See the “Instruction Set Description” for
detailed information.
• Bit 2 – N: Negative Flag
The negative flag N indicates a negative result in an arithmetic or logic operation. See the “Instruction Set Description” for
detailed information.
• Bit 1 – Z: Zero Flag
The zero flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction Set Description” for detailed
information.
• Bit 0 – C: Carry Flag
The carry flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set Description” for detailed
information.
7.4
General Purpose Register File
The register file is optimized for the AVR enhanced RISC instruction set. In order to achieve the required performance and
flexibility, the following input/output schemes are supported by the register file:
●
●
●
●
One 8-bit output operand and one 8-bit result input
Two 8-bit output operands and one 8-bit result input
Two 8-bit output operands and one 16-bit result input
One 16-bit output operand and one 16-bit result input
Figure 7-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 7-2. AVR CPU General Purpose Working Registers
7
0
Addr.
0x00
0x01
0x02
R0
R1
R2
…
R13
R14
R15
R16
R17
…
0x0D
0x0E
0x0F
0x10
0x11
General
Purpose
Working
Registers
R26
R27
R28
R29
R30
R31
0x1A
0x1B
0x1C
0x1D
0x1E
0x1F
X-register low byte
X-register high byte
Y-register low byte
Y-register high byte
Z-register low byte
Z-register high byte
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Most of the instructions operating on the register file have direct access to all registers, and most of them are single cycle
instructions.
As shown in Figure 7-2, each register is also assigned a data memory address, mapping them directly into the first 32
locations of the user data space. Although not being physically implemented as SRAM locations, this memory organization
provides great flexibility in access of the registers, as the X-, Y- and Z-pointer registers can be set to index any register in the
file.
7.4.1 The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These registers are 16-bit address
pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as described
in Figure 7-3.
Figure 7-3. The X-, Y-, and Z-registers
15
XH
XL
0
X-register
7
0
7
0
R27 (0x1B)
R26 (0x1A)
15
YH
YL
0
Y-register
Z-register
7
0
7
0
R29 (0x1D)
R31 (0x1F)
R28 (0x1C)
R30 (0x1E)
15
ZH
ZL
0
7
0
7
0
In the different addressing modes these address registers have functions as fixed displacement, automatic increment, and
automatic decrement (see the instruction set reference for details).
7.5
Stack Pointer
The stack is mainly used for storing temporary data, for storing local variables and for storing return addresses after
interrupts and subroutine calls. Note that the stack is implemented as growing from higher to lower memory locations. The
stack pointer register always points to the top of the stack. The stack pointer points to the data SRAM stack area where the
subroutine and interrupt stacks are located. A stack PUSH command will decrease the stack pointer.
The stack in the data SRAM must be defined by the program before any subroutine calls are executed or interrupts are
enabled. Initial stack pointer value equals the last address of the internal SRAM and the stack pointer must be set to point
above start of the SRAM, see Figure 8-2 on page 17.
See Table 7-1 for stack pointer details.
Table 7-1. Stack Pointer instructions
Instruction
Stack pointer
Description
PUSH
Decremented by 1
Data is pushed onto the stack
CALL
ICALL
RCALL
Decremented by 2
Return address is pushed onto the stack with a subroutine call or interrupt
POP
Incremented by 1
Incremented by 2
Data is popped from the stack
RET
RETI
Return address is popped from the stack with return from subroutine or return
from interrupt
The AVR stack pointer is implemented as two 8-bit registers in the I/O space. The number of bits actually used is
implementation dependent, see Table 7-2 on page 13. Note that the data space in some implementations of the AVR
architecture is so small that only SPL is needed. In this case, the SPH register will not be present.
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7.5.1 SPH and SPL – Stack Pointer High and Stack pointer Low
Bit
15
–
14
–
13
–
12
SP12
SP4
4
11
SP11
SP3
3
10
SP10
SP2
2
9
SP9
SP1
1
8
SP8
SP0
0
0x3E (0x5E)
0x3D (0x5D)
SPH
SPL
SP7
7
SP6
6
SP5
5
Read/Write
Initial Value
R
R
R
R/W
R/W
0/1()
1
R/W
R/W
0/1()
1
R/W
R/W
1/0()
1
R/W
R/W
0
R/W
R/W
0
R/W
0
R/W
0
R/W
0
1
1
1
1
1
Note:
1. Initial values respectively for the ATmega164P-B/324P-B/644P-B
Table 7-2. Stack Pointer Size
Device
Stack Pointer Size
SP[10:0]
ATmega164P-B
ATmega324P-B
ATmega644P-B
SP[11:0]
SP[12:0]
7.6
Instruction Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR CPU is driven by the CPU
clock clkCPU, directly generated from the selected clock source for the chip. No internal clock division is used.
Figure 7-4 on page 13 shows the parallel instruction fetches and instruction executions enabled by the Harvard architecture
and the fast-access register file concept. This is the basic pipelining concept to obtain up to 1MIPS per MHz with the
corresponding unique results for functions per cost, functions per clocks, and functions per power-unit.
Figure 7-4. The Parallel Instruction Fetches and Instruction Executions
T1
T2
T3
T4
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
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Figure 7-5 shows the internal timing concept for the register file. In a single clock cycle an ALU operation using two register
operands is executed, and the result is stored back to the destination register.
Figure 7-5. Single Cycle ALU Operation
T1
T2
T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
7.7
Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate reset vector each have a separate
program vector in the program memory space. All interrupts are assigned individual enable bits which must be written logic
one together with the global interrupt enable bit in the status register in order to enable the interrupt. Depending on the
program counter value, interrupts may be automatically disabled when boot lock bits BLB02 or BLB12 are programmed. This
feature improves software security. See Section 27. “Memory Programming” on page 255 for details.
The lowest addresses in the program memory space are by default defined as the reset and interrupt vectors. The complete
list of vectors is shown in Section 12. “Interrupts” on page 49. The list also determines the priority levels of the different
interrupts. The lower the address the higher is the priority level. RESET has the highest priority, and next is INT0 – the
External Interrupt Request 0. The interrupt vectors can be moved to the start of the boot flash section by setting the IVSEL
bit in the MCU control register (MCUCR). Refer to Section 12. “Interrupts” on page 49 for more information. The reset vector
can also be moved to the start of the boot flash section by programming the BOOTRST fuse, see Section 27. “Memory
Programming” on page 255.
When an interrupt occurs, the global interrupt enable I-bit is cleared and all interrupts are disabled. The user software can
write logic one to the I-bit to enable nested interrupts. All enabled interrupts can then interrupt the current interrupt routine.
The I-bit is automatically set when a return from interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the interrupt flag. For these
interrupts, the program counter is vectored to the actual interrupt vector in order to execute the interrupt handling routine,
and hardware clears the corresponding interrupt flag. Interrupt flags can also be cleared by writing a logic one to the flag bit
position(s) to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is cleared, the Interrupt
flag will be set and remembered until the interrupt is enabled, or the flag is cleared by software. Similarly, if one or more
interrupt conditions occur while the global interrupt enable bit is cleared, the corresponding interrupt flag(s) will be set and
remembered until the global interrupt enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These interrupts do not necessarily
have interrupt flags. If the interrupt condition disappears before the interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one more instruction before any
pending interrupt is served.
Note that the status register is not automatically stored when entering an interrupt routine, nor restored when returning from
an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled. No interrupt will be executed
after the CLI instruction, even if it occurs simultaneously with the CLI instruction. The following example shows how this can
be used to avoid interrupts during the timed EEPROM write sequence.
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Assembly Code Example
in
r16, SREG
; store SREG value
; disable interrupts during timed sequence
EECR, EEMPE ; start EEPROM write
EECR, EEPE
cli
sbi
sbi
out
SREG, r16
; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
__disable_interrupt();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending
interrupts, as shown in this example.
Assembly Code Example
sei
; set Global Interrupt Enable
sleep ; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
__enable_interrupt(); /* set Global Interrupt Enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
7.7.1 Interrupt Response Time
The interrupt execution response for all the enabled AVR interrupts is five clock cycles minimum. After five clock cycles the
program vector address for the actual interrupt handling routine is executed. During these five clock cycle period, the
program counter is pushed onto the stack. The vector is normally a jump to the interrupt routine, and this jump takes three
clock cycles. If an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed before the
interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt execution response time is increased
by five clock cycles. This increase comes in addition to the start-up time from the selected sleep mode.
A return from an interrupt handling routine takes five clock cycles. During these five clock cycles, the program counter (three
bytes) is popped back from the stack, the stack pointer is incremented by three, and the I-bit in SREG is set.
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8.
AVR Memories
8.1
Overview
This section describes the different memories in the ATmega164P-B/324P-B/644P-B. The AVR architecture has two main
memory spaces, the Data Memory and the Program Memory space. In addition, the ATmega164P-B/324P-B/644P-B
features an EEPROM memory for data storage. All three memory spaces are linear and regular.
8.2
In-System Reprogrammable Flash Program Memory
The ATmega164P-B/324P-B/644P-B contains 16/32/64Kbytes on-chip in-system reprogrammable flash memory for
program storage. Since all AVR instructions are 16 or 32 bits wide, the flash is organized as 32/64 × 16. For software
security, the flash program memory space is divided into two sections, boot program section and application program
section.
The flash memory has an endurance of at least 10,000 write/erase cycles. The ATmega164P-B/324P-B/644P-B program
counter (PC) is 15/16 bits wide, thus addressing the 32/64K program memory locations. The operation of boot program
section and associated boot lock bits for software protection are described in detail in Section 27. “Memory Programming” on
page 255. Section 27. “Memory Programming” on page 255 contains a detailed description on flash data serial downloading
using the SPI pins or the JTAG interface.
Constant tables can be allocated within the entire program memory address space (see the LPM – load program memory
instruction description.
Timing diagrams for instruction fetch and execution are presented in Section 7.6 “Instruction Execution Timing” on page 13.
Figure 8-1. Program Memory Map
Program Memory
0x0000
Application Flash Section
Boot Flash Section
0x1FFF/0x3FFF/0x7FFF
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8.3
SRAM Data Memory
Figure 8-2 shows how the ATmega164P-B/324P-B/644P-B SRAM Memory is organized.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported within
the 64 location reserved in the Opcode for the IN and OUT instructions. For the extended I/O space from $060 - $FF in
SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.
The first 4,352 data memory locations address both the register file, the I/O memory, extended I/O memory, and the internal
data SRAM. The first 32 locations address the register file, the next 64 location the standard I/O memory, then 160 locations
of extended I/O memory and the next 4,096 locations address the internal data SRAM.
The five different addressing modes for the data memory cover: Direct, indirect with displacement, indirect, indirect with pre-
decrement, and indirect with post-increment. In the register file, registers R26 to R31 feature the indirect addressing pointer
registers.
The direct addressing reaches the entire data space.
The indirect with displacement mode reaches 63 address locations from the base address given by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-increment, the address registers X,
Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O registers, 160 Extended I/O registers and the 1024/2048/4096 bytes of
internal data SRAM in the ATmega164P-B/324P-B/644P-B are all accessible through all these addressing modes. The
register file is described in Section 7.4 “General Purpose Register File” on page 11.
Figure 8-2. Data Memory Map for ATmega164P-B/324P-B/644P-B
0x0000
32 Registers
0x0020
64 I/O Registers
0x0060
160 Ext I/O Registers
0x0100
Internal SRAM
(1024/2048/4096 *8)
0x04FF/0x08FF/0x10FF
8.3.1 Data Memory Access Times
This section describes the general access timing concepts for internal memory access. The internal data SRAM access is
performed in two clkCPU cycles as described in Figure 8-3.
Figure 8-3. On-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address
Data
Compute Address
Address valid
Write
Read
WR
Data
RD
Memory Access Instruction
Next Instruction
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8.4
EEPROM Data Memory
The ATmega164P-B/324P-B/644P-B contains 512/1/2Kbytes of data EEPROM memory. It is organized as a separate data
space, in which single bytes can be read and written. The EEPROM has an endurance of at least 100,000 write/erase
cycles. The access between the EEPROM and the CPU is described in the following, specifying the EEPROM address
registers, the EEPROM data register, and the EEPROM control register.
For a detailed description of SPI, JTAG and parallel data downloading to the EEPROM, see Section 27.6 “Parallel
Programming Parameters, Pin Mapping, and Commands” on page 259, Section 27.8 “Serial Downloading” on page 270, and
Section 27.10 “Programming via the JTAG Interface” on page 274 respectively.
8.4.1 EEPROM Read/Write Access
The EEPROM access registers are accessible in the I/O space. See Section 8.6 “Register Description” on page 19 for
details. The write access time for the EEPROM is given in Table 8-2 on page 21. A self-timing function, however, lets the
user software detect when the next byte can be written. If the user code contains instructions that write the EEPROM, some
precautions must be taken. In heavily filtered power supplies, VCC is likely to rise or fall slowly on power-up/down. This
causes the device for some period of time to run at a voltage lower than specified as minimum for the clock frequency used.
See Section 8.4.2 “Preventing EEPROM Corruption” on page 18 for details on how to avoid problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to the description of the
EEPROM Control Register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed. When the
EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed.
8.4.2 Preventing EEPROM Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is too low for the CPU and the
EEPROM to operate properly. These issues are the same as for board level systems using EEPROM, and the same design
solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to
the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly,
if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done by enabling the
internal brown-out detector (BOD). If the detection level of the internal BOD does not match the needed detection level, an
external low VCC reset Protection circuit can be used. If a reset occurs while a write operation is in progress, the write
operation will be completed provided that the power supply voltage is sufficient.
8.5
I/O Memory
The I/O space definition of the ATmega164P-B/324P-B/644P-B is shown in Section 30. “Register Summary” on page 323.
All ATmega164P-B/324P-B/644P-B I/Os and peripherals are placed in the I/O space. All I/O locations may be accessed by
the LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32 general purpose working registers and the
I/O space. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions.
In these registers, the value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the instruction
set section for more details. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be
used. When addressing I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported within
the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI
instructions will only operate on the specified bit, and can therefore be used on registers containing such status flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
The I/O and peripherals control registers are explained in later sections.
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The ATmega164P-B/324P-B/644P-B contains three general purpose I/O registers, see Section 8.6 “Register Description” on
page 19. These registers can be used for storing any information, and they are particularly useful for storing global variables
and status flags. General purpose I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the
SBI, CBI, SBIS, and SBIC instructions.
8.6
Register Description
8.6.1 EEARH and EEARL – The EEPROM Address Register
Bit
15
14
13
12
11
10
9
8
EEAR8
EEAR0
0
0x22 (0x42)
0x21 (0x41)
–
–
–
–
EEAR11 EEAR10 EEAR9
EEARH
EEARL
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
7
R
6
R
5
R
4
R
3
R/W
R/W
X
2
R/W
R/W
X
1
R/W
R/W
X
Read/Write
Initial Value
R/W
R/W
X
R/W
0
R/W
0
R/W
0
R/W
0
X
X
X
X
X
X
X
X
• Bits 15:12 – Reserved
These bits are reserved bits in the ATmega164P-B/324P-B/644P-B and will always read as zero.
• Bits 11:0 – EEAR8:0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the 512/1K/2Kbytes EEPROM
space. The EEPROM data bytes are addressed linearly between 0 and 511/1023/2047. The initial value of EEAR is
undefined. A proper value must be written before the EEPROM may be accessed.
8.6.2 EEDR – The EEPROM Data Register
Bit
7
6
5
4
3
2
1
0
0x20 (0x40)
Read/Write
Initial Value
MSB
R/W
0
LSB
R/W
0
EEDR
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
• Bits 7:0 – EEDR7:0: EEPROM Data
For the EEPROM write operation, the EEDR register contains the data to be written to the EEPROM in the address given by
the EEAR Register. For the EEPROM read operation, the EEDR contains the data read out from the EEPROM at the
address given by EEAR.
8.6.3 EECR – The EEPROM Control Register
Bit
7
–
6
–
5
EEPM1
R/W
X
4
EEPM0
R/W
X
3
EERIE
R/W
0
2
EEMPE
R/W
0
1
EEPE
R/W
X
0
EERE
R/W
0
0x1F (0x3F)
Read/Write
Initial Value
EECR
R
0
R
0
• Bits 7:6 – Reserved
These bits are reserved bits in the ATmega164P-B/324P-B/644P-B and will always read as zero.
• Bits 5:4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits
The EEPROM programming mode bit setting defines which programming action that will be triggered when writing EEPE. It
is possible to program data in one atomic operation (erase the old value and program the new value) or to split the erase and
write operations in two different operations. The programming times for the different modes are shown in Table 8-1 on page
20. While EEPE is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to 0b00 unless the
EEPROM is busy programming.
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Table 8-1. EEPROM Mode Bits
EEPM1
EEPM0
Programming Time Operation
0
0
1
1
0
1
0
1
3.4ms
1.8ms
1.8ms
–
Erase and write in one operation (atomic operation)
Erase only
Write only
Reserved for future use
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM ready interrupt if the I bit in SREG is set. Writing EERIE to zero disables the
interrupt. The EEPROM ready interrupt generates a constant interrupt when EEPE is cleared.
• Bit 2 – EEMPE: EEPROM Master Programming Enable
The EEMPE bit determines whether setting EEPE to one causes the EEPROM to be written. When EEMPE is set, setting
EEPE within four clock cycles will write data to the EEPROM at the selected address If EEMPE is zero, setting EEPE will
have no effect. When EEMPE has been written to one by software, hardware clears the bit to zero after four clock cycles.
See the description of the EEPE bit for an EEPROM write procedure.
• Bit 1 – EEPE: EEPROM Programming Enable
The EEPROM write enable signal EEPE is the write strobe to the EEPROM. When address and data are correctly set up,
the EEPE bit must be written to one to write the value into the EEPROM. The EEMPE bit must be written to one before a
logical one is written to EEPE, otherwise no EEPROM write takes place. The following procedure should be followed when
writing the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEPE becomes zero.
2. Wait until SPMEN in SPMCSR becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMPE bit while writing a zero to EEPE in EECR.
6. Within four clock cycles after setting EEMPE, write a logical one to EEPE.
The EEPROM can not be programmed during a CPU write to the flash memory. The software must check that the flash
programming is completed before initiating a new EEPROM write. Step 2 is only relevant if the software contains a boot
loader allowing the CPU to program the flash. If the flash is never being updated by the CPU, step 2 can be omitted. See
Section 27. “Memory Programming” on page 255 for details about boot programming.
Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the EEPROM master write enable will
time-out. If an interrupt routine accessing the EEPROM is interrupting another EEPROM access, the EEAR or EEDR
register will be modified, causing the interrupted EEPROM access to fail. It is recommended to have the global interrupt flag
cleared during all the steps to avoid these problems.
When the write access time has elapsed, the EEPE bit is cleared by hardware. The user software can poll this bit and wait
for a zero before writing the next byte. When EEPE has been set, the CPU is halted for two cycles before the next instruction
is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM read enable signal EERE is the read strobe to the EEPROM. When the correct address is set up in the EEAR
register, the EERE bit must be written to a logic one to trigger the EEPROM read. The EEPROM read access takes one
instruction, and the requested data is available immediately. When the EEPROM is read, the CPU is halted for four cycles
before the next instruction is executed.
The user should poll the EEPE bit before starting the read operation. If a write operation is in progress, it is neither possible
to read the EEPROM, nor to change the EEAR register.
The calibrated Oscillator is used to time the EEPROM accesses. Table 8-2 on page 21 lists the typical programming time for
EEPROM access from the CPU.
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Table 8-2. EEPROM Programming Time
Symbol
Number of Calibrated RC Oscillator Cycles
Typical Programming Time
EEPROM write (from
CPU)
26,368
3.3ms
The following code examples show one assembly and one C function for writing to the EEPROM. The examples assume
that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during execution of these
functions. The examples also assume that no Flash Boot Loader is present in the software. If such code is present, the
EEPROM write function must also wait for any ongoing SPM command to finish.
Assembly Code Example(1)
EEPROM_write:
; Wait for completion of previous write
sbic
rjmp
EECR,EEPE
EEPROM_write
; Set up address (r18:r17) in address register
out
out
EEARH, r18
EEARL, r17
; Write data (r16) to Data Register
out EEDR,r16
; Write logical one to EEMPE
sbi EECR,EEMPE
; Start eeprom write by setting EEPE
sbi
ret
EECR,EEPE
C Code Example(1)
void EEPROM_write(unsigned int uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address and Data Registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}
Note:
1. See Section 4. “About Code Examples” on page 8.
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The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts
are controlled so that no interrupts will occur during execution of these functions.
Assembly Code Example(1)
EEPROM_read:
; Wait for completion of previous write
sbic
rjmp
EECR,EEPE
EEPROM_read
; Set up address (r18:r17) in address register
out
out
EEARH, r18
EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from Data Register
in
r16,EEDR
ret
C Code Example(1)
unsigned char EEPROM_read(unsigned int uiAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEAR = uiAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from Data Register */
return EEDR;
}
Note:
1. See Section 4. “About Code Examples” on page 8.
8.6.4 GPIOR2 – General Purpose I/O Register 2
Bit
7
MSB
R/W
0
6
5
4
3
2
1
0
0x2B (0x4B)
Read/Write
Initial Value
LSB
R/W
0
GPIOR2
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
8.6.5 GPIOR1 – General Purpose I/O Register 1
Bit
7
6
5
4
3
2
1
0
0x2A (0x4A)
Read/Write
Initial Value
MSB
R/W
0
LSB
R/W
0
GPIOR1
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
8.6.6 GPIOR0 – General Purpose I/O Register 0
Bit
7
MSB
R/W
0
6
5
4
3
2
1
0
0x1E (0x3E)
Read/Write
Initial Value
LSB
R/W
0
GPIOR0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
Note:
1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or SRW00 (lower
sector). The ALE pulse in period T4 is only present if the next instruction accesses the RAM (internal or
external).
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9.
System Clock and Clock Options
9.1
Clock Systems and their Distribution
Figure 9-1 presents the principal clock systems in the AVR and their distribution. All of the clocks need not be active at a
given time. In order to reduce power consumption, the clocks to modules not being used can be halted by using different
sleep modes, as described in Section 10. “Power Management and Sleep Modes” on page 34. The clock systems are
detailed below.
Figure 9-1. Clock Distribution
Asynchronous
Timer/Counter
General I/O
Modules
Flash and
EEPROM
ADC
CPU Core
RAM
clkADC
clkI/O
clkCPU
AVR Clock
Control Unit
clkASY
clkFLASH
Reset Logic
Watchdog Timer
Source clock
Watchdog clock
System Clock
Prescaler
Watchdog
Oscillator
Clock
Multiplexer
Timer/Counter
Oscillator
Crystal
Oscillator
Low-frequency
Crystal Oscillator
Calibrated RC
Oscillator
External Clock
9.1.1 CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR core. Examples of such modules are
the general purpose register File, the status register and the data memory holding the stack pointer. Halting the CPU clock
inhibits the core from performing general operations and calculations.
9.1.2 I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART. The I/O clock is also used by
the external interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such
interrupts to be detected even if the I/O clock is halted. Also note that start condition detection in the USI module is carried
out asynchronously when clkI/O is halted, TWI address recognition in all sleep modes.
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9.1.3 Flash Clock – clkFLASH
The flash clock controls operation of the flash interface. The flash clock is usually active simultaneously with the CPU clock.
9.1.4 Asynchronous Timer Clock – clkASY
The asynchronous timer clock allows the asynchronous Timer/Counter to be clocked directly from an external clock or an
external 32kHz clock crystal. The dedicated clock domain allows using this Timer/Counter as a real-time counter even when
the device is in sleep mode.
9.1.5 ADC Clock – clkADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks in order to reduce noise
generated by digital circuitry. This gives more accurate ADC conversion results.
9.2
Clock Sources
The device has the following clock source options, selectable by Flash Fuse bits as shown below. The clock from the
selected source is input to the AVR clock generator, and routed to the appropriate modules.
Table 9-1. Device Clocking Options Select(1)
Device Clocking Option
Low power crystal oscillator
Full swing crystal oscillator
Low frequency crystal oscillator
Internal 128kHz RC oscillator
Calibrated internal RC oscillator
External clock
CKSEL3..0
1111 - 1000
0111 - 0110
0101 - 0100
0011
0010
0000
Reserved
0001
Note:
1. For all fuses “1” means unprogrammed while “0” means programmed.
9.2.1 Default Clock Source
The device is shipped with internal RC oscillator at 8.0MHz and with the fuse CKDIV8 programmed, resulting in 1.0MHz
system clock. The startup time is set to maximum and time-out period enabled. (CKSEL = “0010”, SUT = “10”,
CKDIV8 = “0”). The default setting ensures that all users can make their desired clock source setting using any available
programming interface.
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9.2.2 Clock Startup Sequence
Any clock source needs a sufficient VCC to start oscillating and a minimum number of oscillating cycles before it can be
considered stable.
To ensure sufficient VCC, the device issues an internal reset with a time-out delay (tTOUT) after the device reset is released by
all other reset sources. Section 10.11.7 “On-chip Debug System” on page 37 describes the start conditions for the internal
reset. The delay (tTOUT) is timed from the watchdog oscillator and the number of cycles in the delay is set by the SUTx and
CKSELx fuse bits. The selectable delays are shown in Table 9-2. The frequency of the watchdog oscillator is voltage
dependent as shown in Section 29. “Typical Characteristics” on page 297.
Table 9-2. Number of Watchdog Oscillator Cycles
Typical Time-out (VCC = 5.0V)
Typical Time-out (VCC = 3.0V)
Number of Cycles
0ms
4.1ms
65ms
0ms
4.3ms
69ms
0
512
8K (8,192)
Main purpose of the delay is to keep the AVR in reset until it is supplied with minimum Vcc. The delay will not monitor the
actual voltage and it will be required to select a delay longer than the Vcc rise time. If this is not possible, an internal or
external brown-out detection circuit should be used. A BOD circuit will ensure sufficient Vcc before it releases the reset, and
the time-out delay can be disabled. Disabling the time-out delay without utilizing a brown-out detection circuit is not
recommended.
The oscillator is required to oscillate for a minimum number of cycles before the clock is considered stable. An internal ripple
counter monitors the oscillator output clock, and keeps the internal reset active for a given number of clock cycles. The reset
is then released and the device will start to execute. The recommended oscillator start-up time is dependent on the clock
type, and varies from 6 cycles for an externally applied clock to 32Kcycles for a low frequency crystal.
The start-up sequence for the clock includes both the time-out delay and the start-up time when the device starts up from
reset. When starting up from power-save or power-down mode, Vcc is assumed to be at a sufficient level and only the start-
up time is included.
9.2.3 Clock Source Connections
The pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use as
an on-chip oscillator, as shown in Figure 9-2 on page 25. Either a quartz crystal or a ceramic resonator may be used.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the capacitors depends on the
crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. For ceramic
resonators, the capacitor values given by the manufacturer should be used.
Figure 9-2. Crystal Oscillator Connections
C2
XTAL2
C1
XTAL1
GND
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9.3
Low Power Crystal Oscillator
This crystal oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 output. It gives the lowest power
consumption, but is not capable of driving other clock inputs, and may be more susceptible to noise in noisy environments. In
these cases, refer to Section 9.4 “Full Swing Crystal Oscillator” on page 27.
Some initial guidelines for choosing capacitors for use with crystals are given in Table 9-3. The crystal should be connected
as described in Section 9.2.3 “Clock Source Connections” on page 25.
The low power oscillator can operate in three different modes, each optimized for a specific frequency range. The operating
mode is selected by the fuses CKSEL3..1 as shown in Table 9-3.
Table 9-3. Low Power Crystal Oscillator Operating Modes(1)
Frequency Range (MHz)
0.4 - 0.9
CKSEL3..1(2)
100(3)
101
Recommended Range for Capacitors C1 and C2 (pF)
–
0.9 - 3.0
12 - 22
12 - 22
12 - 22
3.0 - 8.0
110
8.0 - 16.0
111
Notes: 1. If the crystal frequency exceeds the specification of the device (depends on VCC), the CKDIV8 fuse can be pro-
grammed in order to divide the internal frequency by 8. It must be ensured that the resulting divided clock
meets the frequency specification of the device.
2. This is the recommended CKSEL settings for the different frequency ranges.
3. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 fuse together with the SUT1..0 Fuses select the start-up times as shown in Table 9-4.
Table 9-4. Start-up Times for the Low Power Crystal Oscillator Clock Selection
Oscillator Source /
Power Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V)
CKSEL0
SUT1..0
Ceramic resonator, fast rising
power
258 CK
258 CK
1K CK
1K CK
14CK + 4.1ms(1)
14CK + 65ms(1)
14CK(2)
0
00
Ceramic resonator, slowly rising
power
0
0
0
01
10
11
Ceramic resonator, BOD
enabled
Ceramic resonator, fast rising
power
14CK + 4.1ms(2)
Ceramic resonator, slowly rising
power
1K CK
16K CK
16K CK
14CK + 65ms(2)
14CK
1
1
1
00
01
10
Crystal oscillator, BOD enabled
Crystal oscillator, fast rising
power
14CK + 4.1ms
Crystal oscillator, slowly rising
power
16K CK
14CK + 65ms
1
11
Notes: 1. These options should only be used when not operating close to the maximum frequency of the device, and
only if frequency stability at start-up is not important for the application. These options are not suitable for
crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up.
They can also be used with crystals when not operating close to the maximum frequency of the device, and if
frequency stability at start-up is not important for the application.
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9.4
Full Swing Crystal Oscillator
This crystal oscillator is a full swing oscillator, with rail-to-rail swing on the XTAL2 output. This is useful for driving other clock
inputs and in noisy environments. The current consumption is higher than the Low Power Crystal Oscillator in Section 9.3 on
page 26. Note that the full swing crystal oscillator will only operate for Vcc = 2.7 to 5.5V.
Some initial guidelines for choosing capacitors for use with crystals are given in Table 9-6. The crystal should be connected
as described in Section 9.2.3 “Clock Source Connections” on page 25.
The operating mode is selected by the fuses CKSEL3..1 as shown in Table 9-5.
Table 9-5. Full Swing Crystal Oscillator Operating Modes
Recommended Range for Capacitors
Frequency Range(1) (MHz)
CKSEL3..1
C1 and C2 (pF)
0.4 - 16
011
12 - 22
Notes: 1. If the crystal frequency exceeds the specification of the device (depends on VCC), the CKDIV8 fuse can be
programmed in order to divide the internal frequency by 8. It must be ensured that the resulting divided clock
meets the frequency specification of the device.
Table 9-6. Start-up Times for the Full Swing Crystal Oscillator Clock Selection
Oscillator Source / Power
Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V)
CKSEL0
SUT1..0
Ceramic resonator, fast rising
power
258 CK
258 CK
1K CK
1K CK
14CK + 4.1ms(1)
14CK + 65ms(1)
14CK(2)
0
00
Ceramic resonator, slowly rising
power
0
0
0
01
10
11
Ceramic resonator, BOD
enabled
Ceramic resonator, fast rising
power
14CK + 4.1ms(2)
Ceramic resonator, slowly rising
power
1K CK
16K CK
16K CK
14CK + 65ms(2)
14CK
1
1
1
00
01
10
Crystal oscillator, BOD enabled
Crystal oscillator, fast rising
power
14CK + 4.1ms
Crystal oscillator, slowly rising
power
16K CK
14CK + 65ms
1
11
Notes: 1. These options should only be used when not operating close to the maximum frequency of the device, and
only if frequency stability at start-up is not important for the application. These options are not suitable for
crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up. They
can also be used with crystals when not operating close to the maximum frequency of the device, and if fre-
quency stability at start-up is not important for the application.
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9.5
Low Frequency Crystal Oscillator
The low-frequency crystal oscillator is optimized for use with a 32.768kHz watch crystal. When selecting crystals, load
capasitance and crystal’s equivalent series resistance, ESR must be taken into consideration. Both values are specified by
the crystal vendor. ATmega164P-B/324P-B/644P-B oscillator is optimized for very low power consumption, and thus when
selecting crystals, see Table 9-7 on page 28 for maximum ESR recommendations on 9pF and 12.5pF crystals.
Table 9-7. Maximum ESR Recommendation for 32.768kHz Watch Crystal
Crystal CL (pF)
Max ESR [kΩ](1)
9.0
65
30
12.5
Note:
1. Maximum ESR is typical value based on characterization
The Low-frequency crystal oscillator provides an internal load capacitance, see Table on page 28 at each TOSC pin.
Table 9-8. Capacitance for Low-frequency Oscillator
Device
32kHz Osc. Type
System Osc.
Timer Osc.
Cap (Xtal1/Tosc1)
Cap (Xtal2/Tosc2)
18pF
6pF
8pF
6pF
ATmega164P-B/324P-B/644P-B
The capacitance (Ce + Ci) needed at each TOSC pin can be calculated by using:
Ce + Ci = 2 CL – Cs
where:
Ce - is optional external capacitors as described in Figure 9-2 on page 25
Ci - is the pin capacitance in Table 9-8 on page 28
CL - is the load capacitance for a 32.768kHz crystal specified by the crystal vendor.
CS - is the total stray capacitance for one TOSC pin.
Crystals specifying load capacitance (CL) higher than the ones given in the Table 9-8 on page 28, require external capacitors
applied as described in Figure 9-2 on page 25.
Figure 9-3. Crystal Oscillator Connections
Crystals specifying load capacitance (CL) higher than listed in Table 9-8 on page 28, require external capacitors applied as
described in Figure 9-2 on page 25.
To find suitable load capacitance for a 32.768kHz crysal, please consult the crystal datasheet.
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When this oscillator is selected, start-up times are determined by the SUT Fuses and CKSEL0 as shown in Table 9-9.
Table 9-9. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Additional Delay from
Start-up Time from Power-
down and Power-save
Reset
(VCC = 5.0V)
14CK(1)
14CK + 4.1ms(1)
14CK + 65ms(1)
Power Conditions
BOD enabled
CKSEL0
SUT1..0
00
1K CK
1K CK
0
0
0
0
1
1
1
1
Fast rising power
Slowly rising power
01
1K CK
10
Reserved
32K CK
32K CK
32K CK
Reserved
11
BOD enabled
14CK
00
Fast rising power
Slowly rising power
14CK + 4.1ms
14CK + 65ms
01
10
11
Note:
1. These options should only be used if frequency stability at start-up is not important for the application.
9.6
Calibrated Internal RC Oscillator
By default, the Internal RC oscillator provides an approximate 8MHz clock. Though voltage and temperature dependent, this
clock can be very accurately calibrated by the user. See Table 28-3 on page 290 and Section 29.1.8 “Internal Oscillator
Speed” on page 304 and Section 29.2.8 “Internal Oscillator Speed” on page 312 for more details. The device is shipped with
the CKDIV8 Fuse programmed. See Section 9.11 “System Clock Prescaler” on page 31 for more details.
This clock may be selected as the system clock by programming the CKSEL fuses as shown in Table 9-10. If selected, it will
operate with no external components. During reset, hardware loads the pre-programmed default 3V calibration value into the
OSCCAL register and thereby automatically calibrates the RC oscillator for 3V operation. If the device is to be used at 5V
then the alternate RC oscillator 5V calibration byte (Table 26-5 on page 248) can be read from signature row and stored into
the OSCCAL register by the user application program for better 5V frequency accuracy. The accuracy of this calibration is
shown as factory calibration in Table 28-3 on page 290.
By changing the OSCCAL register from SW, see Section 9.12.1 “OSCCAL – Oscillator Calibration Register” on page 32, it is
possible to get a higher calibration accuracy than by using the factory calibration. The accuracy of this calibration is shown
as user calibration in Table 28-3 on page 290.
When this oscillator is used as the chip clock, the watchdog oscillator will still be used for the watchdog timer and for the
reset time-out. For more information on the pre-programmed calibration value, see Section 27.4 “Calibration Byte” on page
258.
Table 9-10. Internal Calibrated RC Oscillator Operating Modes
Frequency Range(2) (MHz)
CKSEL3..0
7.3 - 8.1
0010(1)
Notes: 1. The device is shipped with this option selected.
2. If 8MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8 fuse can be pro-
grammed in order to divide the internal frequency by 8.
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in Table 9-11 on page 30.
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Table 9-11. Start-up times for the Internal Calibrated RC Oscillator clock selection
Start-up Time from Power-down and Additional Delay from Reset
Power Conditions
Power-save
(VCC = 5.0V)
SUT1..0
00
BOD enabled
6 CK
14CK
Fast rising power
Slowly rising power
6 CK
14CK + 4.1ms
14CK + 65ms
01
10(1)
6 CK
Reserved
11
Note:
1. The device is shipped with this option selected.
9.7
128kHz Internal Oscillator
The 128kHz internal oscillator is a low power oscillator providing a clock of 128kHz. The frequency is nominal at 3V and
25°C. This clock may be select as the system clock by programming the CKSEL Fuses to “0011” as shown in Table 9-12.
Table 9-12. 128kHz Internal Oscillator Operating Modes(2)
Nominal Frequency
CKSEL3..0
128kHz
0011
Note:
1. Note that the 128kHz oscillator is a very low power clock source, and is not designed for high accuracy.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 9-13.
Table 9-13. Start-up Times for the 128kHz Internal Oscillator
Start-up Time from Power-down and
Power Conditions
Power-save
Additional Delay from Reset
14CK
SUT1..0
00
BOD enabled
6 CK
Fast rising power
6 CK
14CK + 4ms
01
Slowly rising power
6 CK
14CK + 64ms
10
Reserved
11
9.8
External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in Figure 9-4. To run the device on an
external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 9-4. External Clock Drive Configuration
NC
XTAL2
XTAL1
GND
EXTERNAL
CLOCK
SIGNAL
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When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 9-15.
Table 9-14. Crystal Oscillator Clock Frequency
Nominal Frequency
CKSEL3..0
0 - 16MHz
0000
Table 9-15. Start-up Times for the External Clock Selection
Start-up Time from Power-down and Additional Delay from Reset
Power Conditions
BOD enabled
Power-save
(VCC = 5.0V)
SUT1..0
00
6 CK
14CK
Fast rising power
6 CK
14CK + 4.1ms
14CK + 65ms
01
Slowly rising power
6 CK
10
Reserved
11
When applying an external clock, it is required to avoid sudden changes in the applied clock frequency to ensure stable
operation of the MCU. A variation in frequency of more than 2% from one clock cycle to the next can lead to unpredictable
behavior. If changes of more than 2% is required, ensure that the MCU is kept in reset during the changes.
Note that the system clock prescaler can be used to implement run-time changes of the internal clock frequency while still
ensuring stable operation. Refer to Section 9.11 “System Clock Prescaler” on page 31 for details.
9.9
Timer/Counter Oscillator
ATmega164P-B/324P-B/644P-B uses the same type of crystal oscillator for low-frequency crystal oscillator and
Timer/Counter oscillator. See Section 9.5 “Low Frequency Crystal Oscillator” on page 28 for details on the oscillator and
crystal requirements.
The device can operate its Timer/Counter2 from an external 32.768kHz watch crystal or a external clock source. See
Section 9.2.3 “Clock Source Connections” on page 25 for details.
Applying an external clock source to TOSC1 can be done if EXTCLK in the ASSR register is written to logic one. See Section
17.11.4 “OCR2A – Output Compare Register A” on page 136 for further description on selecting external clock as input
instead of a 32.768kHz watch crystal.
9.10 Clock Output Buffer
The device can output the system clock on the CLKO pin. To enable the output, the CKOUT fuse has to be programmed.
This mode is suitable when the chip clock is used to drive other circuits on the system. The clock also will be output during
reset, and the normal operation of I/O pin will be overridden when the fuse is programmed. Any clock source, including the
internal RC oscillator, can be selected when the clock is output on CLKO. If the system clock prescaler is used, it is the
divided system clock that is output.
9.11 System Clock Prescaler
The ATmega164P-B/324P-B/644P-B has a system clock prescaler, and the system clock can be divided by setting the
Section 9.12.2 “CLKPR – Clock Prescale Register” on page 32. This feature can be used to decrease the system clock
frequency and the power consumption when the requirement for processing power is low. This can be used with all clock
source options, and it will affect the clock frequency of the CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and
clkFLASH are divided by a factor as shown in Table 9-16 on page 33.
When switching between prescaler settings, the system clock prescaler ensures that no glitches occurs in the clock system.
It also ensures that no intermediate frequency is higher than neither the clock frequency corresponding to the previous
setting, nor the clock frequency corresponding to the new setting.
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The ripple counter that implements the prescaler runs at the frequency of the undivided clock, which may be faster than the
CPU's clock frequency. Hence, it is not possible to determine the state of the prescaler - even if it were readable, and the
exact time it takes to switch from one clock division to the other cannot be exactly predicted. From the time the CLKPS
values are written, it takes between T1 + T2 and T1 + 2 × T2 before the new clock frequency is active. In this interval, 2
active clock edges are produced. Here, T1 is the previous clock period, and T2 is the period corresponding to the new
prescaler setting.
To avoid unintentional changes of clock frequency, a special write procedure must be followed to change the CLKPS bits:
1. Write the clock prescaler change enable (CLKPCE) bit to one and all other bits in CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted.
9.12 Register Description
9.12.1 OSCCAL – Oscillator Calibration Register
Bit
7
6
5
4
3
2
1
0
(0x66)
CAL7
R/W
CAL6
R/W
CAL5
R/W
CAL4
R/W
CAL3
R/W
CAL2
R/W
CAL1
R/W
CAL0
R/W
OSCCAL
Read/Write
Initial Value
Device Specific Calibration Value
• Bits 7:0 – CAL7:0: Oscillator Calibration Value
The oscillator calibration register is used to trim the calibrated internal RC oscillator to remove process variations from the
oscillator frequency. A pre-programmed calibration value is automatically written to this register during chip reset, giving the
Factory calibrated frequency as specified in Table 28-3 on page 290. The application software can write this register to
change the oscillator frequency. The oscillator can be calibrated to frequencies as specified in Table 28-3 on page 290.
Calibration outside that range is not guaranteed.
Note that this oscillator is used to time EEPROM and flash write accesses, and these write times will be affected accordingly.
If the EEPROM or flash are written, do not calibrate to more than 8.8MHz. Otherwise, the EEPROM or flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the lowest frequency range,
setting this bit to 1 gives the highest frequency range. The two frequency ranges are overlapping, in other words a setting of
OSCCAL = 0x7F gives a higher frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00 gives the lowest frequency in
that range, and a setting of 0x7F gives the highest frequency in the range.
9.12.2 CLKPR – Clock Prescale Register
Bit
7
CLKPCE
R/W
6
–
5
–
4
–
3
2
1
0
(0x61)
CLKPS3 CLKPS2 CLKPS1 CLKPS0
R/W R/W R/W R/W
See Bit Description
CLKPR
Read/Write
Initial Value
R
0
R
0
R
0
0
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE bit is only updated when the
other bits in CLKPR are simultaneously written to zero. CLKPCE is cleared by hardware four cycles after it is written or when
CLKPS bits are written. Rewriting the CLKPCE bit within this time-out period does neither extend the time-out period, nor
clear the CLKPCE bit.
• Bits 3:0 – CLKPS3:0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system clock. These bits can be
written run-time to vary the clock frequency to suit the application requirements. As the divider divides the master clock input
to the MCU, the speed of all synchronous peripherals is reduced when a division factor is used. The division factors are
given in Table 9-16 on page 33.
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The CKDIV8 fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed, the CLKPS bits will be reset to
“0000”. If CKDIV8 is programmed, CLKPS bits are reset to “0011”, giving a division factor of 8 at start up. This feature should
be used if the selected clock source has a higher frequency than the maximum frequency of the device at the present
operating conditions. Note that any value can be written to the CLKPS bits regardless of the CKDIV8 fuse setting. The
Application software must ensure that a sufficient division factor is chosen if the selected clock source has a higher
frequency than the maximum frequency of the device at the present operating conditions. The device is shipped with the
CKDIV8 fuse programmed.
Table 9-16. Clock Prescaler Select
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Clock Division Factor
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
1
2
4
8
16
32
64
128
256
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
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10. Power Management and Sleep Modes
10.1 Overview
Sleep modes enable the application to shut down unused modules in the MCU, thereby saving power. The AVR provides
various sleep modes allowing the user to tailor the power consumption to the application’s requirements.
When enabled, the brown-out detector (BOD) actively monitors the power supply voltage during the sleep periods. To further
save power, it is possible to disable the BOD in some sleep modes. See Section 10.3 “BOD Disable” on page 35 for more
details.
10.2 Sleep Modes
Figure 9-1 on page 23 presents the different clock systems in the ATmega164P-B/324P-B/644P-B, and their distribution.
The figure is helpful in selecting an appropriate sleep mode. Table 10-1 shows the different sleep modes, their wake up
sources and BOD disable ability.
Table 10-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes.
Active Clock Domains
Oscillators
Wake-up Sources
Sleep Mode
Idle
X
X
X
X
X
X
X
X(2)
X(2)
X
X
X
X
X
X
X
X
X
X
X
X
X
X(2)
X
X
X
X
X
X
X
X
X
X
X
ADCNRM
Power-down
Power-save
Standby(1)
X
X
X
X
X
X(2)
X(2)
X
X
X
X
Extended standby
X(2)
Notes: 1. Only recommended with external crystal or resonator selected as clock source.
2. If Timer/Counter2 is running in asynchronous mode.
To enter any of the sleep modes, the SE bit in SMCR must be written to logic one and a SLEEP instruction must be
executed. The SM2, SM1, and SM0 bits in the SMCR register select which sleep mode will be activated by the SLEEP
instruction. See Table 10-2 on page 38 for a summary.
If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for four cycles
in addition to the start-up time, executes the interrupt routine, and resumes execution from the instruction following SLEEP.
The contents of the register file and SRAM are unaltered when the device wakes up from sleep. If a reset occurs during
sleep mode, the MCU wakes up and executes from the reset vector.
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10.3 BOD Disable
When the brown-out detector (BOD) is enabled by BODLEVEL fuses, Table 27-3 on page 256, the BOD is actively
monitoring the power supply voltage during a sleep period. To save power, it is possible to disable the BOD by software for
some of the sleep modes, see Table 10-1 on page 34. The sleep mode power consumption will then be at the same level as
when BOD is globally disabled by fuses. If BOD is disabled in software, the BOD function is turned off immediately after
entering the sleep mode. Upon wake-up from sleep, BOD is automatically enabled again. This ensures safe operation in
case the VCC level has dropped during the sleep period.
When the BOD has been disabled, the wake-up time from sleep mode will be approximately 60µs to ensure that the BOD is
working correctly before the MCU continues executing code.
BOD disable is controlled by bit 6, BODS (BOD Sleep) in the control register MCUCR, see Section 10.12.2 “MCUCR – MCU
Control Register” on page 38. Writing this bit to one turns off the BOD in relevant sleep modes, while a zero in this bit keeps
BOD active. Default setting keeps BOD active, i.e. BODS set to zero.
Writing to the BODS bit is controlled by a timed sequence and an enable bit, see Section 10.12.2 “MCUCR – MCU Control
Register” on page 38.
10.4 Idle Mode
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle mode, stopping the CPU but
allowing the SPI, USART, analog comparator, ADC, 2-wire serial interface, Timer/Counters, watchdog, and the interrupt
system to continue operating. This sleep mode basically halts clkCPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the timer overflow and
USART transmit complete interrupts. If wake-up from the analog comparator interrupt is not required, the analog comparator
can be powered down by setting the ACD bit in the analog comparator control and status register – ACSR. This will reduce
power consumption in idle mode. If the ADC is enabled, a conversion starts automatically when this mode is entered.
10.5 ADC Noise Reduction Mode
When the SM2..0 bits are written to 001, the SLEEP instruction makes the MCU enter ADC noise reduction mode, stopping
the CPU but allowing the ADC, the external interrupts, 2-wire serial interface address match, Timer/Counter2 and the
watchdog to continue operating (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while allowing
the other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements. If the ADC is enabled, a
conversion starts automatically when this mode is entered. Apart form the ADC conversion complete interrupt, only an
external reset, a watchdog system reset, a watchdog interrupt, a brown-out reset, a 2-wire serial interface interrupt, a
Timer/Counter2 interrupt, an SPM/EEPROM ready interrupt, an external level interrupt on INT7:4 or a pin change interrupt
can wake up the MCU from ADC noise reduction mode.
10.6 Power-down Mode
When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter power-down mode. In this mode, the
external oscillator is stopped, while the external interrupts, the 2-wire serial interface, and the watchdog continue operating
(if enabled). Only an external reset, a watchdog reset, a brown-out reset, 2-wire serial interface address match, an external
level interrupt on PCINT7:4, an external interrupt on INT2:0, or a pin change interrupt can wake up the MCU. This sleep
mode basically halts all generated clocks, allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from power-down mode, the changed level must be held for some
time to wake up the MCU. Refer to Section 13. “External Interrupts” on page 53 for details.
When waking up from power-down mode, there is a delay from the wake-up condition occurs until the wake-up becomes
effective. This allows the clock to restart and become stable after having been stopped. The wake-up period is defined by the
same CKSEL fuses that define the reset time-out period, as described in Section 9.2 “Clock Sources” on page 24.
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10.7 Power-save Mode
When the SM2:0 bits are written to 011, the SLEEP instruction makes the MCU enter power-save mode. This mode is
identical to power-down, with one exception:
If Timer/Counter2 is enabled, it will keep running during sleep. The device can wake up from either timer overflow or output
compare event from Timer/Counter2 if the corresponding Timer/Counter2 interrupt enable bits are set in TIMSK2, and the
global interrupt enable bit in SREG is set.
If Timer/Counter2 is not running, power-down mode is recommended instead of power-save mode.
The Timer/Counter2 can be clocked both synchronously and asynchronously in power-save mode. If the Timer/Counter2 is
not using the asynchronous clock, the Timer/Counter oscillator is stopped during sleep. If the Timer/Counter2 is not using
the synchronous clock, the clock source is stopped during sleep. Note that even if the synchronous clock is running in
power-save, this clock is only available for the Timer/Counter2.
10.8 Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the SLEEP instruction makes the
MCU enter standby mode. This mode is identical to power-down with the exception that the oscillator is kept running. From
standby mode, the device wakes up in six clock cycles.
10.9 Extended Standby Mode
When the SM2..0 bits are 111 and an external crystal/resonator clock option is selected, the SLEEP instruction makes the
MCU enter extended standby mode. This mode is identical to power-save mode with the exception that the oscillator is kept
running. From extended standby mode, the device wakes up in six clock cycles.
10.10 Power Reduction Register
The power reduction register (PRR), see Section 10.12.3 “PRR0 – Power Reduction Register 0” on page 39, provides a
method to stop the clock to individual peripherals to reduce power consumption. The current state of the peripheral is frozen
and the I/O registers can not be read or written. Resources used by the peripheral when stopping the clock will remain
occupied, hence the peripheral should in most cases be disabled before stopping the clock. Waking up a peripheral, which is
done by clearing the bit in PRR, puts the peripheral in the same state as before shutdown.
Peripheral shutdown can be used in Idle mode and Active mode to significantly reduce the overall power consumption. In all
other sleep modes, the clock is already stopped.
10.11 Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR controlled system. In
general, sleep modes should be used as much as possible, and the sleep mode should be selected so that as few as
possible of the device’s functions are operating. All functions not needed should be disabled. In particular, the following
modules may need special consideration when trying to achieve the lowest possible power consumption.
10.11.1 Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering any
sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion. Refer to Section
23. “ADC - Analog-to-digital Converter” on page 207 for details on ADC operation.
10.11.2 Analog Comparator
When entering Idle mode, the analog comparator should be disabled if not used. When entering ADC noise reduction mode,
the analog comparator should be disabled. In other sleep modes, the analog comparator is automatically disabled. However,
if the analog comparator is set up to use the internal voltage reference as input, the analog comparator should be disabled in
all sleep modes. Otherwise, the internal voltage reference will be enabled, independent of sleep mode. Refer to Section 22.
“AC - Analog Comparator” on page 204 for details on how to configure the analog comparator.
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10.11.3 Brown-out Detector
If the brown-out detector is not needed by the application, this module should be turned off. If the brown-out detector is
enabled by the BODLEVEL fuses, it will be enabled in all sleep modes, and hence, always consume power. In the deeper
sleep modes, this will contribute significantly to the total current consumption. Refer to Section 11.1.4 “Brown-out Detection”
on page 42 for details on how to configure the brown-out detector.
10.11.4 Internal Voltage Reference
The internal voltage reference will be enabled when needed by the brown-out detection, the analog comparator or the ADC.
If these modules are disabled as described in the sections above, the internal voltage reference will be disabled and it will
not be consuming power. When turned on again, the user must allow the reference to start up before the output is used. If
the reference is kept on in sleep mode, the output can be used immediately. Refer to Section 11.2 “Internal Voltage
Reference” on page 43 for details on the start-up time.
10.11.5 Watchdog Timer
If the watchdog timer is not needed in the application, the module should be turned off. If the watchdog timer is enabled, it
will be enabled in all sleep modes, and hence, always consume power. In the deeper sleep modes, this will contribute
significantly to the total current consumption. Refer to Section 11.3 “Watchdog Timer” on page 44 for details on how to
configure the watchdog timer.
10.11.6 Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The most important is then to ensure
that no pins drive resistive loads. In sleep modes where both the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped,
the input buffers of the device will be disabled. This ensures that no power is consumed by the input logic when not needed.
In some cases, the input logic is needed for detecting wake-up conditions, and it will then be enabled. Refer to the section
Section 14.2.5 “Digital Input Enable and Sleep Modes” on page 61 for details on which pins are enabled. If the input buffer is
enabled and the input signal is left floating or have an analog signal level close to VCC/2, the input buffer will use excessive
power.
For analog input pins, the digital input buffer should be disabled at all times. An analog signal level close to VCC/2 on an input
pin can cause significant current even in active mode. Digital input buffers can be disabled by writing to the digital input
disable registers (DIDR1 and DIDR0). Refer to Section 22.3.3 “DIDR1 – Digital Input Disable Register 1” on page 206 and
Section 23.9.5 “DIDR0 – Digital Input Disable Register 0” on page 224 for details.
10.11.7 On-chip Debug System
If the on-chip debug system is enabled by the OCDEN Fuse and the chip enters sleep mode, the main clock source is
enabled, and hence, always consumes power. In the deeper sleep modes, this will contribute significantly to the total current
consumption.
There are three alternative ways to disable the OCD system:
●
●
●
Disable the OCDEN fuse
Disable the JTAGEN fuse
Write one to the JTD bit in MCUCR
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10.12 Register Description
10.12.1 SMCR – Sleep Mode Control Register
The sleep mode control register contains control bits for power management.
Bit
7
–
6
–
5
–
4
–
3
2
1
0
SE
R/W
0
0x33 (0x53)
Read/Write
Initial Value
SM2
R/W
0
SM1
R/W
0
SM0
R/W
0
SMCR
R
0
R
0
R
0
R
0
• Bits 3, 2, 1 – SM2:0: Sleep Mode Select Bits 2, 1, and 0
These bits select between the five available sleep modes as shown in Table 10-2.
Table 10-2. Sleep Mode Select
SM2
SM1
SM0
0
Sleep Mode
Idle
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
1
ADC noise reduction
Power-down
Power-save
Reserved
0
1
0
1
Reserved
Standby(1)
Extended standby(1)
0
1
Note:
1. Standby modes are only recommended for use with external crystals or resonators.
• Bit 0 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP instruction is executed. To
avoid the MCU entering the sleep mode unless it is the programmer’s purpose, it is recommended to write the sleep enable
(SE) bit to one just before the execution of the SLEEP instruction and to clear it immediately after waking up.
10.12.2 MCUCR – MCU Control Register
Bit
7
6
BODS
R/W
0
5
BODSE
R/W
0
4
3
–
2
–
1
IVSEL
R/W
0
0
IVCE
R/W
0
0x35 (0x55)
Read/Write
Initial Value
JTD
R/W
0
PUD
R/W
0
MCUCR
R
0
R
0
• Bit 6 – BODS: BOD Sleep
The BODS bit must be written to logic one in order to turn off BOD during sleep, see Table 10-1 on page 34. Writing to the
BODS bit is controlled by a timed sequence and an enable bit, BODSE in MCUCR. To disable BOD in relevant sleep modes,
both BODS and BODSE must first be set to one. Then, to set the BODS bit, BODS must be set to one and BODSE must be
set to zero within four clock cycles.
The BODS bit is active three clock cycles after it is set. A sleep instruction must be executed while BODS is active in order to
turn off the BOD for the actual sleep mode. The BODS bit is automatically cleared after three clock cycles.
• Bit 5 – BODSE: BOD Sleep Enable
BODSE enables setting of BODS control bit, as explained in BODS bit description. BOD disable is controlled by a timed
sequence.
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10.12.3 PRR0 – Power Reduction Register 0
Bit
7
6
5
4
3
2
1
0
(0x64)
PRTWI PRTIM2 PRTIM0 PRUSART1 PRTIM1 PRSPI PRUSART0 PRADC PRR0
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
• Bit 7 – PRTWI: Power Reduction TWI
Writing a logic one to this bit shuts down the TWI by stopping the clock to the module. When waking up the TWI again, the
TWI should be re initialized to ensure proper operation.
• Bit 6 – PRTIM2: Power Reduction Timer/Counter2
Writing a logic one to this bit shuts down the Timer/Counter2 module in synchronous mode (AS2 is 0). When the
Timer/Counter2 is enabled, operation will continue like before the shutdown.
• Bit 5 – PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0 is enabled, operation will
continue like before the shutdown.
• Bit 4 – PRUSART1: Power Reduction USART1
Writing a logic one to this bit shuts down the USART1 by stopping the clock to the module. When waking up the USART1
again, the USART1 should be reinitialized to ensure proper operation.
• Bit 3 – PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 module. When the Timer/Counter1 is enabled, operation will
continue like before the shutdown.
• Bit 2 – PRSPI: Power Reduction Serial Peripheral Interface
Writing a logic one to this bit shuts down the serial peripheral Interface by stopping the clock to the module. When waking up
the SPI again, the SPI should be re initialized to ensure proper operation.
• Bit 1 – PRUSART0: Power Reduction USART0
Writing a logic one to this bit shuts down the USART0 by stopping the clock to the module. When waking up the USART0
again, the USART0 should be reinitialized to ensure proper operation.
• Bit 0 – PRADC: Power Reduction ADC
Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down. The analog comparator
cannot use the ADC input MUX when the ADC is shut down.
10.12.4 PRR1 – Power Reduction Register 1
Bit
7
–
6
–
5
–
4
–
3
–
2
–
1
–
0
PRTIM3
R/W
0
(0x65)
PRR1
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R
0
R
0
R
0
• Bit 7:1 – Reserved
• Bit 0 – PRTIM3: Power Reduction Timer/Counter3
Writing a logic one to this bit shuts down the Timer/Counter3 module. When the Timer/Counter3 is enabled, operation will
continue like before the shutdown.
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11. System Control and Reset
11.1 Resetting the AVR
During reset, all I/O registers are set to their initial values, and the program starts execution from the reset vector. The
instruction placed at the reset vector must be a JMP – absolute jump – instruction to the reset handling routine. If the
program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed at
these locations. This is also the case if the reset vector is in the application section while the interrupt vectors are in the boot
section or vice versa. The circuit diagram in Figure 11-1 on page 41 shows the reset logic. Section 28.5 “System and Reset
Characteristics” on page 291 defines the electrical parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source goes active. This does not require
any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal reset. This allows the power to
reach a stable level before normal operation starts. The time-out period of the delay counter is defined by the user through
the SUT and CKSEL Fuses. The different selections for the delay period are presented in Section 9.2 “Clock Sources” on
page 24.
11.1.1 Reset Sources
The ATmega164P-B/324P-B/644P-B has five sources of reset:
●
●
Power-on reset: The MCU is reset when the supply voltage is below the power-on reset threshold (VPOT).
External reset: The MCU is reset when a low level is present on the RESET pin for longer than the minimum pulse
length.
●
●
Watchdog reset: The MCU is reset when the watchdog timer period expires and the watchdog is enabled.
Brown-out reset: The MCU is reset when the supply voltage VCC is below the brown-out reset threshold (VBOT) and the
brown-out detector is enabled.
●
JTAG AVR reset: The MCU is reset as long as there is a logic one in the reset register, one of the scan chains of the
JTAG system. Refer to Section 25. “IEEE 1149.1 (JTAG) Boundary-scan” on page 231 for details.
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Figure 11-1. Reset Logic
DATA BUS
MCU Status
Register (MCUSR)
Power-on Reset
Circuit
VCC
Brown-out
BODLEVEL [2 to 0]
RESET
Reset Circuit
Pull-up Resistor
Q
SPIKE
FILTER
Reset Circuit
S
R
JTAG Reset
Register
Watchdog
Timer
Watchdog
Oscillator
Delay Counters
CK
Clock
Generator
TIMEOUT
CKSEL[3:0]
SUT[1:0]
11.1.2 Power-on Reset
A power-on reset (POR) pulse is generated by an on-chip detection circuit. The detection level is defined in Section 28.5
“System and Reset Characteristics” on page 291. The POR is activated whenever VCC is below the detection level. The POR
circuit can be used to trigger the start-up Reset, as well as to detect a failure in supply voltage.
A power-on reset (POR) circuit ensures that the device is reset from power-on. Reaching the power-on reset threshold
voltage invokes the delay counter, which determines how long the device is kept in RESET after VCC rise. The RESET signal
is activated again, without any delay, when VCC decreases below the detection level.
Figure 11-2. MCU Start-up, RESET Tied to VCC
VPOT
VCC
VRST
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
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Figure 11-3. MCU Start-up, RESET Extended Externally
VPOT
VDD
VRST
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
11.1.3 External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the minimum pulse width (see
“System and Reset Characteristics” on page 291) will generate a reset, even if the clock is not running. Shorter pulses are
not guaranteed to generate a reset. When the applied signal reaches the Reset Threshold Voltage – VRST – on its positive
edge, the delay counter starts the MCU after the Time-out period – tTOUT – has expired.
Figure 11-4. External Reset During Operation
V
CC
RESET
VRST
t
TOUT
TIME-OUT
INTERNAL
RESET
11.1.4 Brown-out Detection
ATmega164P-B/324P-B/644P-B has an on-chip brown-out detection (BOD) circuit for monitoring the VCC level during
operation by comparing it to a fixed trigger level. The trigger level for the BOD can be selected by the BODLEVEL fuses. The
trigger level has a hysteresis to ensure spike free brown-out detection. The hysteresis on the detection level should be
interpreted as VBOT+ = VBOT + VHYST/2 and VBOT- = VBOT – VHYST/2.
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure 11-5 on page 43), the
brown-out reset is immediately activated. When VCC increases above the trigger level (VBOT+ in Figure 11-5 on page 43), the
delay counter starts the MCU after the time-out period tTOUT has expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for longer than tBOD given in Section
28.5 “System and Reset Characteristics” on page 291.
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Figure 11-5. Brown-out Reset During Operation
VCC
VBOT+
VBOT-
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
11.1.5 Watchdog Reset
When the watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse,
the delay timer starts counting the time-out period tTOUT. Refer to Section 11.3 “Watchdog Timer” on page 44 for details on
operation of the watchdog timer.
Figure 11-6. Watchdog Reset During Operation
VCC
RESET
1 CK Cycle
WDT
TIME-OUT
tTOUT
RESET
Time-OUT
INTERNAL
RESET
11.2 Internal Voltage Reference
ATmega164P-B/324P-B/644P-B features an internal bandgap reference. This reference is used for brown-out detection, and
it can be used as an input to the analog comparator or the ADC.
11.2.1 Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given in Section
28.5 “System and Reset Characteristics” on page 291. To save power, the reference is not always turned on. The reference
is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL [2:0] fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting the ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow the
reference to start up before the output from the analog comparator or ADC is used. To reduce power consumption in
power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering
power-down mode.
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11.3 Watchdog Timer
11.3.1 Features
●
●
Clocked from separate on-chip oscillator
3 operating modes
●
●
●
Interrupt
System reset
Interrupt and system reset
●
●
Selectable time-out period from 16ms to 8s
Possible hardware fuse watchdog always on (WDTON) for fail-safe mode
11.3.2 Overview
ATmega164P-B/324P-B/644P-B has an enhanced watchdog timer (WDT). The WDT is a timer counting cycles of a separate
on-chip 128kHz oscillator. The WDT gives an interrupt or a system reset when the counter reaches a given time-out value. In
normal operation mode, it is required that the system uses the WDR - Watchdog Timer Reset - instruction to restart the
counter before the time-out value is reached. If the system doesn't restart the counter, an interrupt or system reset will be
issued.
Figure 11-7. Watchdog Timer
Watchdog
128kHz
Prescaler
Oscillator
WDP0
WDP1
WDP2
WDP3
WATCHDOG
RESET
WDE
MCU RESET
WDIF
INTERRUPT
WDIE
In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can be used to wake the device from
sleep-modes, and also as a general system timer. One example is to limit the maximum time allowed for certain operations,
giving an interrupt when the operation has run longer than expected. In System Reset mode, the WDT gives a reset when
the timer expires. This is typically used to prevent system hang-up in case of runaway code. The third mode, Interrupt and
System Reset mode, combines the other two modes by first giving an interrupt and then switch to system reset mode. This
mode will for instance allow a safe shutdown by saving critical parameters before a system reset.
The watchdog always on (WDTON) fuse, if programmed, will force the watchdog timer to system reset mode. With the fuse
programmed the system reset mode bit (WDE) and Interrupt mode bit (WDIE) are locked to 1 and 0 respectively. To further
ensure program security, alterations to the watchdog set-up must follow timed sequences. The sequence for clearing WDE
and changing time-out configuration is as follows:
1. In the same operation, write a logic one to the watchdog change enable bit (WDCE) and WDE. A logic one must
be written to WDE regardless of the previous value of the WDE bit.
2. Within the next four clock cycles, write the WDE and watchdog prescaler bits (WDP) as desired, but with the
WDCE bit cleared. This must be done in one operation.
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The following code example shows one assembly and one C function for turning off the watchdog Timer. The example
assumes that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during the
execution of these functions.
Assembly Code Example(1)
WDT_off:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Clear WDRF in MCUSR
in
andi r16, ~(1<<WDRF)
out MCUSR, r16
r16, MCUSR
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional time-out
in
ori
out
r16, WDTCSR
r16, (1<<WDCE) | (1<<WDE)
WDTCSR, r16
; Turn off WDT
ldi
out
r16, (0<<WDE)
WDTCSR, r16
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_off(void)
{
__disable_interrupt();
__watchdog_reset();
/* Clear WDRF in MCUSR */
MCUSR &= ~(1<<WDRF);
/* Write logical one to WDCE and WDE */
/* Keep old prescaler setting to prevent unintentional time-out
*/
}
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCSR = 0x00;
__enable_interrupt();
Notes: 1. The example code assumes that the part specific header file is included.
2. If the Watchdog is accidentally enabled, for example by a runaway pointer or brown-out condition, the device
will be reset and the watchdog Timer will stay enabled. If the code is not set up to handle the watchdog, this
might lead to an eternal loop of time-out resets. To avoid this situation, the application software should always
clear the watchdog system reset flag (WDRF) and the WDE control bit in the initialization routine, even if the
watchdog is not in use.
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The following code example shows one assembly and one C function for changing the time-out value of the Watchdog
Timer.
Assembly Code Example(1)
WDT_Prescaler_Change:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
in
ori
out
r16, WDTCSR
r16, (1<<WDCE) | (1<<WDE)
WDTCSR, r16
; -- Got four cycles to set the new values from here -
; Set new prescaler(time-out) value = 64K cycles (~0.5 s)
ldi
out
r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)
WDTCSR, r16
; -- Finished setting new values, used 2 cycles -
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_Prescaler_Change(void)
{
__disable_interrupt();
__watchdog_reset();
/* Start timed equence */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCSR = (1<<WDE) | (1<<WDP2) | (1<<WDP0);
__enable_interrupt();
}
Notes: 1. The example code assumes that the part specific header file is included.
2. The watchdog timer should be reset before any change of the WDP bits, since a change in the WDP bits can
result in a time-out when switching to a shorter time-out period.
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11.4 Register Description
11.4.1 MCUSR – MCU Status Register
The MCU status register provides information on which reset source caused an MCU reset.
Bit
7
–
6
–
5
–
4
3
2
1
0
0x34 (0x54)
Read/Write
Initial Value
JTRF
R/W
WDRF
R/W
BORF
R/W
EXTRF
R/W
PORF
R/W
MCUSR
R
0
R
0
R
0
See Bit Description
• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG reset register selected by the JTAG instruction
AVR_RESET. This bit is reset by a power-on reset, or by writing a logic zero to the flag.
• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a watchdog reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.
• Bit 2 – BORF: Brown-out Reset Flag
This bit is set if a brown-out reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an external reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a power-on reset occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the reset flags to identify a reset condition, the user should read and then reset the MCUSR as early as
possible in the program. If the register is cleared before another reset occurs, the source of the reset can be found by
examining the reset flags.
11.4.2 WDTCSR – Watchdog Timer Control Register
Bit
7
WDIF
R/W
0
6
WDIE
R/W
0
5
WDP3
R/W
0
4
WDCE
R/W
0
3
2
WDP2
R/W
0
1
WDP1
R/W
0
0
WDP0
R/W
0
(0x60)
WDE
R/W
X
WDTCSR
Read/Write
Initial Value
• Bit 7 - WDIF: Watchdog Interrupt Flag
This bit is set when a time-out occurs in the watchdog timer and the watchdog timer is configured for interrupt. WDIF is
cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, WDIF is cleared by writing a
logic one to the flag. When the I-bit in SREG and WDIE are set, the watchdog time-out Interrupt is executed.
• Bit 6 - WDIE: Watchdog Interrupt Enable
When this bit is written to one and the I-bit in the status register is set, the watchdog Interrupt is enabled. If WDE is cleared
in combination with this setting, the watchdog timer is in Interrupt Mode, and the corresponding interrupt is executed if time-
out in the watchdog timer occurs.
If WDE is set, the watchdog timer is in interrupt and system reset mode. The first time-out in the watchdog timer will set
WDIF. Executing the corresponding interrupt vector will clear WDIE and WDIF automatically by hardware (the watchdog
goes to system reset mode). This is useful for keeping the watchdog timer security while using the interrupt. To stay in
interrupt and system reset mode, WDIE must be set after each interrupt. This should however not be done within the
interrupt service routine itself, as this might compromise the safety-function of the watchdog system reset mode. If the
interrupt is not executed before the next time-out, a system reset will be applied.
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Table 11-1. Watchdog Timer Configuration
WDTON
WDE
WDIE
Mode
Action on Time-out
None
1
1
1
0
0
1
0
1
0
Stopped
Interrupt mode
System reset mode
Interrupt
Reset
Interrupt, then go to system reset
mode
1
0
1
x
1
x
Interrupt and system reset mode
System reset mode
Reset
• Bit 4 - WDCE: Watchdog Change Enable
This bit is used in timed sequences for changing WDE and prescaler bits. To clear the WDE bit, and/or change the prescaler
bits, WDCE must be set.
Once written to one, hardware will clear WDCE after four clock cycles.
• Bit 3 - WDE: Watchdog System Reset Enable
WDE is overridden by WDRF in MCUSR. This means that WDE is always set when WDRF is set. To clear WDE, WDRF
must be cleared first. This feature ensures multiple resets during conditions causing failure, and a safe start-up after the
failure.
• Bit 5, 2:0 - WDP3:0: Watchdog Timer Prescaler 3, 2, 1 and 0
The WDP3:0 bits determine the watchdog timer prescaling when the watchdog timer is running. The different prescaling
values and their corresponding time-out periods are shown in Table 11-2 on page 48.
Table 11-2. Watchdog Timer Prescale Select
Typical Time-out at
WDP3
WDP2
WDP1
WDP0
Number of WDT Oscillator Cycles
VCC = 5.0V
16ms
32ms
64ms
0.125s
0.25s
0.5s
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
2K (2048) cycles
4K (4096) cycles
8K (8192) cycles
16K (16384) cycles
32K (32768) cycles
64K (65536) cycles
128K (131072) cycles
256K (262144) cycles
512K (524288) cycles
1024K (1048576) cycles
1.0s
2.0s
4.0s
8.0s
Reserved
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12. Interrupts
12.1 Overview
This section describes the specifics of the interrupt handling as performed in ATmega164P-B/324P-B/644P-B. For a general
explanation of the AVR interrupt handling, refer to Section 7.7 “Reset and Interrupt Handling” on page 14.
12.2 Interrupt Vectors in ATmega164P-B/324P-B/644P-B
Table 12-1. Reset and Interrupt Vectors
Vector No. Program Address(2) Source
Interrupt Definition
External pin, power-on reset, brown-out reset, watchdog
reset, and JTAG AVR reset
1
$0000(1)
RESET
2
$0002
$0004
$0006
$0008
$000A
$000C
$000E
$0010
$0012
$0014
$0016
$0018
$001A
$001C
$001E
$0020
$0022
$0024
$0026
$0028
$002A
$002C
$002E
$0030
$0032
$0034
$0036
INT0
External interrupt request 0
External interrupt request 1
External interrupt request 2
Pin change interrupt request 0
Pin change interrupt request 1
Pin change interrupt request 2
Pin change interrupt request 3
Watchdog time-out interrupt
Timer/Counter2 compare match A
Timer/Counter2 compare match B
Timer/Counter2 overflow
3
INT1
4
INT2
5
PCINT0
6
PCINT1
7
PCINT2
8
PCINT3
9
WDT
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
TIMER2_COMPA
TIMER2_COMPB
TIMER2_OVF
TIMER1_CAPT
TIMER1_COMPA
TIMER1_COMPB
TIMER1_OVF
TIMER0_COMPA
TIMER0_COMPB
TIMER0_OVF
SPI_STC
Timer/Counter1 capture event
Timer/Counter1 compare match A
Timer/Counter1 compare match B
Timer/Counter1 overflow
Timer/Counter0 compare match A
Timer/Counter0 compare match B
Timer/Counter0 overflow
SPI serial transfer complete
USART0 Rx complete
USART0_RX
USART0_UDRE
USART0_TX
ANALOG_COMP
ADC
USART0 data register empty
USART0 Tx complete
Analog comparator
ADC conversion complete
EEPROM ready
EE_READY
TWI
2-wire serial interface
SPM_READY
USART1_RX
USART1_UDRE
USART1_TX
Store program memory ready
USART1 Rx Complete
$0038
$003A
$003C
USART1 Data Register Empty
USART1 Tx Complete
Notes: 1. When the BOOTRST fuse is programmed, the device will jump to the boot loader address at reset, see
Section 27. “Memory Programming” on page 255.
2. When the IVSEL bit in MCUCR is set, interrupt vectors will be moved to the start of the boot flash section. The
address of each Interrupt Vector will then be the address in this table added to the start address of the boot
flash Section.
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Table 12-2 shows reset and Interrupt Vectors placement for the various combinations of BOOTRST and IVSEL settings. If
the program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed
at these locations. This is also the case if the reset vector is in the application section while the interrupt vectors are in the
boot section or vice versa.
Table 12-2. Reset and Interrupt Vectors Placement(1)
BOOTRST
IVSEL
Reset Address
0x0000
Interrupt Vectors Start Address
0x0002
1
1
0
0
0
1
0
1
0x0000
Boot reset address + 0x0002
0x0002
Boot reset address
Boot reset address
Boot reset address + 0x0002
Note:
1. The boot reset address is shown in Table 26-10 on page 251. For the BOOTRST fuse “1” means
unprogrammed while “0” means programmed.
The most typical and general program setup for the reset and interrupt vector addresses in ATmega164P-B/324P-B/644P-B
is:
Address
0x0000
0x0002
0x0004
0x0006
0x0008
0x000A
0x000C
0x000E
0x0010
0x0012
0x0014
0x0016
0x0018
0x001A
0x001C
0x001E
0x0020
0x0022
0x0024
0x0026
0x0028
0x002A
0x002C
0x002E
0x0030
0x0032
0x0034
0x0036
0x0038
0x003A
0x003C
;
Labels Code
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
jmp
Comments
; Reset
RESET
INT0
; IRQ0
; IRQ1
INT1
INT2
; IRQ2
; PCINT0
PCINT0
PCINT1
; PCINT1
; PCINT2
; PCINT3
PCINT2
PCINT3
WDT
; Watchdog Timeout
; Timer2 CompareA
; Timer2 CompareB
; Timer2 Overflow
; Timer1 Capture
; Timer1 CompareA
; Timer1 CompareB
; Timer1 Overflow
; Timer0 CompareA
; Timer0 CompareB
; Timer0 Overflow
; SPI Transfer Complete
; USART0 RX Complete
TIM2_COMPA
TIM2_COMPB
TIM2_OVF
TIM1_CAPT
TIM1_COMPA
TIM1_COMPB
TIM1_OVF
TIM0_COMPA
TIM0_COMPB
TIM0_OVF
SPI_STC
USART0_RXC
USART0_UDRE ; USART0,UDR Empty
USART0_TXC
ANA_COMP
ADC
; USART0 TX Complete
; Analog Comparator
; ADC Conversion Complete
; EEPROM Ready
EE_RDY
TWI
; 2-wire Serial
; SPM Ready
; USART1 RX Complete
SPM_RDY
USART1_RXC
USART1_UDRE ; USART1,UDR Empty
USART1_TXC ; USART1 TX Complete
0x003E
0x003F
0x0040
0x0041
0x0042
0x0043
...
RESET: ldi
out
ldi
r16,high(RAMEND); Main program start
SPH,r16
; Set Stack Pointer to top of RAM
r16,low(RAMEND)
SPL,r16
out
sei
; Enable interrupts
<instr> xxx
... ...
...
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When the BOOTRST fuse is unprogrammed, the boot section size set to 8Kbytes and the IVSEL bit in the MCUCR register
is set before any interrupts are enabled, the most typical and general program setup for the reset and interrupt vector
addresses is:
Address
0x00000
0x00001
0x00002
0x00003
0x00004
0x00005
;
Labels Code
RESET: ldi
out
Comments
r16,high(RAMEND); Main program start
SPH,r16
; Set Stack Pointer to top of RAM
ldi
out
r16,low(RAMEND)
SPL,r16
sei
<instr> xxx
; Enable interrupts
.org 0x1F002
0x1F002
0x1F004
...
jmp
jmp
...
jmp
EXT_INT0
EXT_INT1
...
; IRQ0 Handler
; IRQ1 Handler
;
0x1FO36
SPM_RDY
; SPM Ready Handler
When the BOOTRST fuse is programmed and the boot section size set to 8Kbytes, the most typical and general program
setup for the reset and interrupt vector addresses is:
Address
.org 0x0002
0x00002
0x00004
...
Labels Code
Comments
jmp
jmp
...
jmp
EXT_INT0
EXT_INT1
...
; IRQ0 Handler
; IRQ1 Handler
;
0x00036
;
SPM_RDY
; SPM Ready Handler
.org 0x1F000
0x1F000
0x1F001
0x1F002
0x1F003
0x1F004
0x1F005
RESET: ldi
out
ldi
r16,high(RAMEND); Main program start
SPH,r16
; Set Stack Pointer to top of RAM
r16,low(RAMEND)
SPL,r16
out
sei
; Enable interrupts
<instr> xxx
When the BOOTRST fuse is programmed, the boot section size set to 8Kbytes and the IVSEL bit in the MCUCR register is
set before any interrupts are enabled, the most typical and general program setup for the reset and interrupt vector
addresses is:
Address
;
Labels Code
Comments
.org 0x1F000
0x1F000
0x1F002
0x1F004
...
jmp
jmp
jmp
...
jmp
RESET
; Reset handler
; IRQ0 Handler
; IRQ1 Handler
;
EXT_INT0
EXT_INT1
...
0x1F036
;
SPM_RDY
; SPM Ready Handler
0x1F03E
0x1F03F
0x1F040
0x1F041
0x1F042
0x1FO43
RESET: ldi
out
ldi
r16,high(RAMEND); Main program start
SPH,r16
; Set Stack Pointer to top of RAM
r16,low(RAMEND)
SPL,r16
; Enable interrupts
out
sei
<instr> xxx
12.2.1 Moving Interrupts Between Application and Boot Space
The general interrupt control register controls the placement of the interrupt vector table.
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12.3 Register Description
12.3.1 MCUCR – MCU Control Register
.
Bit
7
6
BODS
R/W
0
5
BODSE
R/W
0
4
3
–
2
–
1
IVSEL
R/W
0
0
IVCE
R/W
0
0x35 (0x55)
Read/Write
Initial Value
JTD
R/W
0
PUD
R/W
0
MCUCR
R
0
R
0
• Bit 1 – IVSEL: Interrupt Vector Select
When the IVSEL bit is cleared (zero), the interrupt vectors are placed at the start of the flash memory. When this bit is set
(one), the interrupt vectors are moved to the beginning of the boot loader section of the flash. The actual address of the start
of the boot flash section is determined by the BOOTSZ fuses. Refer to the Section 27. “Memory Programming” on page 255
for details. To avoid unintentional changes of interrupt vector tables, a special write procedure must be followed to change
the IVSEL bit:
1. Write the interrupt vector change enable (IVCE) bit to one.
2. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled in the cycle IVCE is set, and
they remain disabled until after the instruction following the write to IVSEL. If IVSEL is not written, interrupts remain disabled
for four cycles. The I-bit in the status register is unaffected by the automatic disabling.
Note:
If interrupt vectors are placed in the boot loader section and boot lock bit BLB02 is programmed, interrupts are
disabled while executing from the application section. If interrupt vectors are placed in the application section
and boot lock bit BLB12 is programed, interrupts are disabled while executing from the boot loader section.
Refer to the section Section 27. “Memory Programming” on page 255 for details on boot lock bits.
• Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is cleared by hardware four cycles after it
is written or when IVSEL is written. Setting the IVCE bit will disable interrupts, as explained in the IVSEL description above.
See the following code example.
Assembly code example
Move_interrupts:
; Get MCUCR
in
mov
r16, MCUCR
r17, r16
; Enable change of Interrupt Vectors
ori
out
r16, (1<<IVCE)
MCUCR, r16
; Move interrupts to Boot Flash section
ori
out
ret
r17, (1<<IVSEL)
MCUCR, r17
C code example
void Move_interrupts(void)
{
uchar temp;
/* GET MCUCR*/
temp = MCUCR;
/* Enable change of Interrupt Vectors */
MCUCR = temp|(1<<IVCE);
/* Move interrupts to Boot Flash section */
MCUCR = temp|(1<<IVSEL);
}
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13. External Interrupts
13.1 Overview
The external interrupts are triggered by the INT2:0 pin or any of the PCINT31:0 pins. Observe that, if enabled, the interrupts
will trigger even if the INT2:0 or PCINT31:0 pins are configured as outputs. This feature provides a way of generating a
software interrupt.
The pin change interrupt PCI3 will trigger if any enabled PCINT31:24 pin toggle, Pin change interrupt PCI2 will trigger if any
enabled PCINT23:16 pin toggles, pin change interrupt PCI1 if any enabled PCINT15:8 toggles and pin change interrupts
PCI0 will trigger if any enabled PCINT7:0 pin toggles. PCMSK3, PCMSK2, PCMSK1 and PCMSK0 registers control which
pins contribute to the pin change interrupts. Pin change interrupts on PCINT31:0 are detected asynchronously. This implies
that these interrupts can be used for waking the part also from sleep modes other than idle mode.
The external interrupts can be triggered by a falling or rising edge or a low level. This is set up as indicated in the
specification for the external interrupt control registers – EICRA (INT2:0). When the external interrupt is enabled and is
configured as level triggered, the interrupt will trigger as long as the pin is held low. Low level interrupts and the edge
interrupt on INT2:0 are detected asynchronously. This implies that these interrupts can be used for waking the part also from
sleep modes other than idle mode. The I/O clock is halted in all sleep modes except idle mode.
Note that if a level triggered interrupt is used for wake-up from power-down, the required level must be held long enough for
the MCU to complete the wake-up to trigger the level interrupt. If the level disappears before the end of the start-up time, the
MCU will still wake up, but no interrupt will be generated. The start-up time is defined by the SUT and CKSEL fuses as
described in Section 9. “System Clock and Clock Options” on page 23.
13.2 Register Description
13.2.1 EICRA – External Interrupt Control Register A
The external interrupt control register A contains control bits for interrupt sense control.
Bit
7
–
6
–
5
ISC21
R/W
0
4
ISC20
R/W
0
3
ISC11
R/W
0
2
ISC10
R/W
0
1
ISC01
R/W
0
0
ISC00
R/W
0
(0x69)
EICRA
Read/Write
Initial Value
R
0
R
0
• Bits 7:6 – Reserved
These bits are reserved in the Atmel ATmega164P-B/324P-B/644P-B, and will always read as zero.
• Bits 5:0 – ISC21, ISC20 – ISC00, ISC00: External Interrupt 2 - 0 Sense Control Bits
The external interrupts 2 - 0 are activated by the external pins INT2:0 if the SREG I-flag and the corresponding interrupt
mask in the EIMSK is set. The level and edges on the external pins that activate the interrupts are defined in
Table 13-1 on page 54. Edges on INT2:INT0 are registered asynchronously. Pulses on INT2:0 pins wider than the minimum
pulse width given in Section 28.6 “External Interrupts Characteristics” on page 291 will generate an interrupt. Shorter pulses
are not guaranteed to generate an interrupt. If low level interrupt is selected, the low level must be held until the completion
of the currently executing instruction to generate an interrupt. If enabled, a level triggered interrupt will generate an interrupt
request as long as the pin is held low.
When changing the ISCn bit, an interrupt can occur. Therefore, it is recommended to first disable INTn by clearing its
interrupt enable bit in the EIMSK register. Then, the ISCn bit can be changed. Finally, the INTn interrupt flag should be
cleared by writing a logical one to its interrupt flag bit (INTFn) in the EIFR register before the interrupt is re-enabled.
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Table 13-1. Interrupt Sense Control(1)
ISCn1
ISCn0
Description
0
0
1
1
0
1
0
1
The low level of INTn generates an interrupt request.
Any edge of INTn generates asynchronously an interrupt request.
The falling edge of INTn generates asynchronously an interrupt request.
The rising edge of INTn generates asynchronously an interrupt request.
Note:
1. n = 2, 1 or 0.
When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its interrupt enable bit in the
EIMSK register. Otherwise an interrupt can occur when the bits are changed.
13.2.2 EIMSK – External Interrupt Mask Register
Bit
7
–
6
–
5
–
4
–
3
–
2
1
0
IINT0
R/W
0
0x1D (0x3D)
Read/Write
Initial Value
INT2
R/W
0
INT1
R/W
0
EIMSK
R
0
R
0
R
0
R
0
R
0
• Bits 2:0 – INT2:0: External Interrupt Request 2 - 0 Enable
When an INT2:0 bit is written to one and the I-bit in the status register (SREG) is set (one), the corresponding external pin
interrupt is enabled. The interrupt sense control bits in the external Interrupt control register, EICRA, defines whether the
external interrupt is activated on rising or falling edge or level sensed. Activity on any of these pins will trigger an interrupt
request even if the pin is enabled as an output. This provides a way of generating a software interrupt.
13.2.3 EIFR –External Interrupt Flag Register
Bit
7
–
6
–
5
–
4
–
3
–
2
INTF2
R/W
0
1
INTF1
R/W
0
0
IINTF0
R/W
0
0x1C (0x3C)
Read/Write
Initial Value
EIFR
R/W
0
R
0
R
0
R
0
R
0
• Bits 2:0 – INTF2:0: External Interrupt Flags 2 - 0
When an edge or logic change on the INT2:0 pin triggers an interrupt request, INTF2:0 becomes set (one). If the I-bit in
SREG and the corresponding interrupt enable bit, INT2:0 in EIMSK, are set (one), the MCU will jump to the interrupt vector.
The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
These flags are always cleared when INT2:0 are configured as level interrupt. Note that when entering sleep mode with the
INT2:0 interrupts disabled, the input buffers on these pins will be disabled. This may cause a logic change in internal signals
which will set the INTF2:0 flags. See Section 14.2.5 “Digital Input Enable and Sleep Modes” on page 61 for more
information.
13.2.4 PCICR – Pin Change Interrupt Control Register
Bit
7
–
6
–
5
–
4
–
3
PCIE3
R/W
0
2
PCIE2
R/W
0
1
PCIE1
R/W
0
0
PCIE0
R/W
0
(0x68)
PCICR
Read/Write
Initial Value
R
0
R
0
R
0
R
0
• Bit 3 – PCIE3: Pin Change Interrupt Enable 3
When the PCIE3 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 3 is enabled. Any
change on any enabled PCINT31:24 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request
is executed from the PCI3 interrupt vector. PCINT31:24 pins are enabled individually by the PCMSK3 register.
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• Bit 2 – PCIE2: Pin Change Interrupt Enable 2
When the PCIE2 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 2 is enabled. Any
change on any enabled PCINT23:16 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request
is executed from the PCI2 interrupt vector. PCINT23:16 pins are enabled individually by the PCMSK2 register.
• Bit 1 – PCIE1: Pin Change Interrupt Enable 1
When the PCIE1 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 1 is enabled. Any
change on any enabled PCINT15:8 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request is
executed from the PCI1 interrupt vector. PCINT15:8 pins are enabled individually by the PCMSK1 register.
• Bit 0 – PCIE0: Pin Change Interrupt Enable 0
When the PCIE0 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 0 is enabled. Any
change on any enabled PCINT7:.0 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request is
executed from the PCI0 interrupt vector. PCINT7:0 pins are enabled individually by the PCMSK0 register.
13.2.5 PCIFR – Pin Change Interrupt Flag Register
Bit
7
6
5
–
4
–
3
PCIF3
R/W
0
2
PCIF2
R/W
0
1
PCIF1
R/W
0
0
PCIF0
R/W
0
0x1B (0x3B)
Read/Write
Initial Value
PCIFR
R
0
R
0
R
0
R
0
• Bit 3– PCIF3: Pin Change Interrupt Flag 3
When a logic change on any PCINT31:24 pin triggers an interrupt request, PCIF3 becomes set (one). If the I-bit in SREG
and the PCIE3 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when
the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 2 – PCIF2: Pin Change Interrupt Flag 2
When a logic change on any PCINT23:16 pin triggers an interrupt request, PCIF2 becomes set (one). If the I-bit in SREG
and the PCIE2 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when
the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 1 – PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT15:8 pin triggers an interrupt request, PCIF1 becomes set (one). If the I-bit in SREG and
the PCIE1 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when the
interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 0 – PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT7:0 pin triggers an interrupt request, PCIF0 becomes set (one). If the I-bit in SREG and
the PCIE0 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when the
interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
13.2.6 PCMSK3 – Pin Change Mask Register 3
Bit
7
6
5
4
3
2
1
0
(0x73)
PCINT31 PCINT30 PCINT29 PCINT28 PCINT27 PCINT26 PCINT25 PCINT24 PCMSK3
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
• Bit 7:0 – PCINT31:24: Pin Change Enable Mask 31:24
Each PCINT31:24-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT31:24 is set and
the PCIE3 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT31:24 is cleared, pin
change interrupt on the corresponding I/O pin is disabled.
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13.2.7 PCMSK2 – Pin Change Mask Register 2
Bit
7
6
5
4
3
2
1
0
(0x6D)
PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 PCMSK2
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
• Bit 7:0 – PCINT23:16: Pin Change Enable Mask 23..16
Each PCINT23:16-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT23:16 is set and
the PCIE2 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT23:16 is cleared, pin
change interrupt on the corresponding I/O pin is disabled.
13.2.8 PCMSK1 – Pin Change Mask Register 1
Bit
7
6
5
4
3
2
1
0
(0x6C)
PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9
PCINT8 PCMSK1
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
• Bit 7:0 – PCINT15:8: Pin Change Enable Mask 15..8
Each PCINT15:8-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT15:8 is set and
the PCIE1 bit in EIMSK is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT15:8 is cleared, pin
change interrupt on the corresponding I/O pin is disabled.
13.2.9 PCMSK0 – Pin Change Mask Register 0
Bit
7
PCINT7
R/W
0
6
PCINT6
R/W
0
5
PCINT5
R/W
0
4
PCINT4
R/W
0
3
PCINT3
R/W
0
2
PCINT2
R/W
0
1
PCINT1
R/W
0
0
(0x6B)
PCINT0 PCMSK0
Read/Write
Initial Value
R/W
0
• Bit 7:0 – PCINT7:0: Pin Change Enable Mask 7..0
Each PCINT7:0 bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT7:0 is set and the
PCIE0 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT7..0 is cleared, pin change
interrupt on the corresponding I/O pin is disabled.
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14. I/O-Ports
14.1 Overview
All AVR® ports have true read-modify-write functionality when used as general digital I/O ports. This means that the direction
of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI
instructions. The same applies when changing drive value (if configured as output) or enabling/disabling of pull-up resistors
(if configured as input). Each output buffer has symmetrical drive characteristics with both high sink and source capability.
The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with
a supply-voltage invariant resistance. All I/O pins have protection diodes to both VCC and ground as indicated in Figure 14-1.
Refer to Section 28. “Electrical Characteristics” on page 287 for a complete list of parameters.
Figure 14-1. I/O Pin Equivalent Schematic
Rpu
Pxn
Logic
See Figure
”General Digital I/O”
for Details
Cpin
All registers and bit references in this section are written in general form. A lower case “x” represents the numbering letter for
the port, and a lower case “n” represents the bit number. However, when using the register or bit defines in a program, the
precise form must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The
physical I/O registers and bit locations are listed in Section 14.4 “Register Description” on page 72.
Three I/O memory address locations are allocated for each port, one each for the data register – PORTx, data direction
register – DDRx, and the port input pins – PINx. The port input pins I/O location is read only, while the data register and the
data direction register are read/write. However, writing a logic one to a bit in the PINx register, will result in a toggle in the
corresponding bit in the data register. In addition, the pull-up disable – PUD bit in MCUCR disables the pull-up function for all
pins in all ports when set.
Using the I/O port as general digital I/O is described in Section 14.2 “Ports as General Digital I/O” on page 58. Most port pins
are multiplexed with alternate functions for the peripheral features on the device. How each alternate function interferes with
the port pin is described in Section 14.3 “Alternate Port Functions” on page 62. Refer to the individual module sections for a
full description of the alternate functions. Note that enabling the alternate function of some of the port pins does not affect the
use of the other pins in the port as general digital I/O.
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14.2 Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 14-2 shows a functional description of one
I/O-port pin, here generically called Pxn.
Figure 14-2. General Digital I/O(1)
PUD
Q
Q
D
DDxn
CLR
WDx
RDx
RESET
1
0
Pxn
Q
D
PORTxn
Q
CLR
WPx
RESET
WRx
SLEEP
RRx
RPx
Synchronizer
D
L
Q
Q
D
Q
Q
PINxn
CLKI/O
PUD:
SLEEP:
CLKI/O
PULLUP DISABLE
SLEEP CONTROL
I/O CLOCK
WDx:
RDx:
WRx:
RRx:
RPx:
WPx:
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
:
WRITE PORTx REGISTER
Note:
1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP, and PUD
are common to all ports.
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14.2.1 Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in
Section 14.4 “Register Description” on page 72, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at
the PORTx I/O address, and the PINxn bits at the PINx I/O address.
The DDxn bit in the DDRx register selects the direction of this pin. If DDxn is written logic one, Pxn is configured as an output
pin. If DDxn is written logic zero, Pxn is configured as an input pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated. To switch the
pull-up resistor off, PORTxn has to be written logic zero or the pin has to be configured as an output pin. The port pins are
tri-stated when reset condition becomes active, even if no clocks are running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is
written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).
14.2.2 Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI instruction
can be used to toggle one single bit in a port.
14.2.3 Switching Between Input and Output
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn} = 0b11), an intermediate
state with either pull-up enabled {DDxn, PORTxn} = 0b01) or output low ({DDxn, PORTxn} = 0b10) must occur. Normally, the
pull-up enabled state is fully acceptable, as a high-impedant environment will not notice the difference between a strong high
driver and a pull-up. If this is not the case, the PUD bit in the MCUCR register can be set to disable all pull-ups in all ports.
Switching between input with pull-up and output low generates the same problem. The user must use either the tri-state
({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn} = 0b11) as an intermediate step.
Table 14-1 summarizes the control signals for the pin value.
Table 14-1. Port Pin Configurations
DDxn
PORTxn
PUD (in MCUCR)
I/O
Pull-up
No
Comment
0
0
0
1
1
0
1
1
0
1
X
0
Input
Tri-state (hi-Z)
Input
Yes
No
Pxn will source current if ext. pulled low.
Tri-state (hi-Z)
1
Input
X
X
Output
Output
No
Output low (sink)
No
Output high (source)
14.2.4 Reading the Pin Value
Independent of the setting of data direction bit DDxn, the port pin can be read through the PINxn register bit. As shown in
Figure 14-2 on page 58, the PINxn register bit and the preceding latch constitute a synchronizer. This is needed to avoid
metastability if the physical pin changes value near the edge of the internal clock, but it also introduces a delay.
Figure 14-3 on page 60 shows a timing diagram of the synchronization when reading an externally applied pin value. The
maximum and minimum propagation delays are denoted tpd,max and tpd,min respectively.
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Figure 14-3. Synchronization when Reading an Externally Applied Pin value
SYSTEM CLK
INSTRUCTIOS
SYNC LATCH
PINxn
XXX
XXX
in r17, PINx
r17
0x00
0xFF
tpd, max
tpd, min
Consider the clock period starting shortly after the first falling edge of the system clock. The latch is closed when the clock is
low, and goes transparent when the clock is high, as indicated by the shaded region of the “SYNC LATCH” signal. The signal
value is latched when the system clock goes low. It is clocked into the PINxn register at the succeeding positive clock edge.
As indicated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed between ½ and 1½
system clock period depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 14-4. The out
instruction sets the “SYNC LATCH” signal at the positive edge of the clock. In this case, the delay tpd through the
synchronizer is 1 system clock period.
Figure 14-4. Synchronization when Reading a Software Assigned Pin Value
SYSTEM CLK
r16
INSTRUCTIOS
SYNC LATCH
PINxn
0xFF
out PORTx, r16
nop
in r17, PINx
r17
0x00
0xFF
tpd
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The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 7 as
input with pull-ups assigned to port pins 6 and 7. The resulting pin values are read back again, but as previously discussed,
a nop instruction is included to be able to read back the value recently assigned to some of the pins.
Assembly Code Example(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi
ldi
out
out
r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
PORTB,r16
DDRB,r17
; Insert nop for synchronization
nop
; Read port pins
in
r16,PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
__no_operation();
/* Read port pins */
i = PINB;
...
Note:
1. For the assembly program, two temporary registers are used to minimize the time from pull-ups are set on pins
0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as
strong high drivers.
14.2.5 Digital Input Enable and Sleep Modes
As shown in Figure 14-2 on page 58, the digital input signal can be clamped to ground at the input of the schmitt-trigger. The
signal denoted SLEEP in the figure, is set by the MCU sleep controller in power-down mode, power-save mode, and standby
mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled, SLEEP
is active also for these pins. SLEEP is also overridden by various other alternate functions as described in Section 14.3
“Alternate Port Functions” on page 62.
If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as “interrupt on rising edge, falling
edge, or any logic change on Pin” while the external interrupt is not enabled, the corresponding external interrupt flag will be
set when resuming from the above mentioned sleep mode, as the clamping in these sleep mode produces the requested
logic change.
14.2.6 Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level. Even though most of the digital
inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current
consumption in all other modes where the digital inputs are enabled (reset, active mode and idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up. In this case, the pull-up will
be disabled during reset. If low power consumption during reset is important, it is recommended to use an external pull-up or
pull-down. Connecting unused pins directly to VCC or GND is not recommended, since this may cause excessive currents if
the pin is accidentally configured as an output.
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14.3 Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 14-5 shows how the port pin control
signals from the simplified Figure 14-2 on page 58 can be overridden by alternate functions. The overriding signals may not
be present in all port pins, but the figure serves as a generic description applicable to all port pins in the AVR®
microcontroller family.
Figure 14-5. Alternate Port Functions(1)
PUOExn
1
0
PUOVxn
PUD
DDOExn
DDOVxn
1
0
Q
Q
D
DDxn
CLR
WDx
RDx
RESET
PVOExn
PVOVxn
1
0
Pxn
1
Q
D
0
PORTxn
PTOExn
Q
DIEOExn
DIEOVxn
CLR
1
0
RESET
WRx
WPx
RRx
RPx
SLEEP
Synchronizer
SET
D
L
Q
Q
D
Q
Q
PINxn
CLR
CLR
CLKI/O
DIxn
AIOxn
PUOExn:
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
DIEOVxn:
SLEEP:
Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
Pxn PORT VALUE OVERRIDE ENABLE
Pxn PORT VALUE OVERRIDE VALUE
Pxn DIGITAL INPUT ENABLE OVERRIDE ENABLE
Pxn DIGITAL INPUT ENABLE OVERRIDE VALUE
SLEEP CONTROL
PUD:
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
CLK:I/O
DIxn:
AIOxn:
PULL-UP DISABLE
WRITE DDRx
READ DDRx
READ PORTx REGISTER
WRITE PORTx
READ PORTx PIN
WRITE PINx
I/O CLOCK
DIGITAL INPUT PIN n ON PORTx
ANALOG INPUT/OUTPUT PIN n ON PORTx
PTOExn:
Pxn, PORT TOGGLE OVERRIDE ENABLE
Note:
1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP, and PUD
are common to all ports. All other signals are unique for each pin.
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Table 14-2 summarizes the function of the overriding signals. The pin and port indexes from Figure 14-5 on page 62 are not
shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function.
Table 14-2. Generic Description of Overriding Signals for Alternate Functions
Signal Name
Full Name
Description
If this signal is set, the pull-up enable is controlled by the PUOV signal. If
PUOE
Pull-up override enable this signal is cleared, the pull-up is enabled when
{DDxn, PORTxn, PUD} = 0b010.
If PUOE is set, the pull-up is enabled/disabled when PUOV is set/cleared,
regardless of the setting of the DDxn, PORTxn, and PUD register bits.
PUOV
DDOE
DDOV
PVOE
Pull-up override value
If this signal is set, the output driver enable is controlled by the DDOV
signal. If this signal is cleared, the output driver is enabled by the DDxn
register bit.
Data direction override
enable
Data direction override If DDOE is set, the output driver is enabled/disabled when DDOV is
Value
set/cleared, regardless of the setting of the DDxn register bit.
If this signal is set and the output driver is enabled, the port value is
controlled by the PVOV signal. If PVOE is cleared, and the output driver is
enabled, the port Value is controlled by the PORTxn register bit.
Port value override
enable
If PVOE is set, the port value is set to PVOV, regardless of the setting of the
PORTxn register bit.
PVOV
PTOE
Port value override value
Port toggle override
enable
If PTOE is set, the PORTxn register bit is inverted.
If this bit is set, the digital input enable is controlled by the DIEOV signal. If
this signal is cleared, the digital input enable is determined by MCU state
(normal mode, sleep mode).
Digital input enable
override enable
DIEOE
DIEOV
Digital input enable
override value
If DIEOE is set, the digital input is enabled/disabled when DIEOV is
set/cleared, regardless of the MCU state (normal mode, sleep mode).
This is the digital input to alternate functions. In the figure, the signal is
connected to the output of the schmitt trigger but before the synchronizer.
Unless the digital input is used as a clock source, the module with the
alternate function will use its own synchronizer.
DI
Digital input
This is the analog input/output to/from alternate functions. The signal is
connected directly to the pad, and can be used bi-directionally.
AIO
Analog input/output
The following subsections shortly describe the alternate functions for each port, and relate the overriding signals to the
alternate function. Refer to the alternate function description for further details.
14.3.1 Alternate Functions of Port A
The port A pins with alternate functions are shown in Table 14-3.
Table 14-3. Port A Pins Alternate Functions
Port Pin
PA7
Alternate Function
ADC7 (ADC input channel 7) PCINT7 (pin change interrupt 7)
ADC6 (ADC input channel 6) PCINT6 (pin change interrupt 6)
ADC5 (ADC input channel 5) PCINT5 (pin change interrupt 5)
ADC4 (ADC input channel 4) PCINT4 (pin change interrupt 4)
ADC3 (ADC input channel 3) PCINT3 (pin change interrupt 3)
ADC2 (ADC input channel 2) PCINT2 (pin change interrupt 2)
ADC1 (ADC input channel 1) PCINT1 (pin change interrupt 1)
ADC0 (ADC input channel 0) PCINT0 (pin change interrupt 0)
PA6
PA5
PA4
PA3
PA2
PA1
PA0
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• ADC7:0/PCINT7:0 – Port A, Bit 7:0
ADC7:0, analog to digital converter, channels 7:0.
PCINT7:0, pin change interrupt source 7:0: The PA7:0 pins can serve as external interrupt sources.
Table 14-4 and Table 14-5 relate the alternate functions of port A to the overriding signals shown in Figure 14-5 on page 62.
Table 14-4. Overriding Signals for Alternate Functions in PA7:PA4
Signal Name
PUOE
PA7/ADC7/PCINT7 PA6/ADC6/PCINT6
PA5/ADC5/PCINT5
PA4/ADC4/PCINT4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
PUOV
DDOE
DDOV
PVOE
PVOV
PCINT7 × PCIE0 + PCINT6 × PCIE0 +
PCINT5 × PCIE0 +
ADC5D
PCINT4 × PCIE0 +
ADC4D
DIEOE
ADC7D
ADC6D
DIEOV
DI
PCINT7 × PCIE0
PCINT7 INPUT
ADC7 INPUT
PCINT6 × PCIE0
PCINT6 INPUT
ADC6 INPUT
PCINT5 × PCIE0
PCINT5 INPUT
ADC5 INPUT
PCINT4 × PCIE0
PCINT4 INPUT
ADC4 INPUT
AIO
Table 14-5. Overriding Signals for Alternate Functions in PA3:PA0
Signal Name
PUOE
PA3/ADC3/PCINT3 PA2/ADC2/PCINT2
PA1/ADC1/PCINT1
PA0/ADC0/PCINT0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
PUOV
DDOE
DDOV
PVOE
PVOV
PCINT3 × PCIE0 + PCINT2 × PCIE0 +
PCINT1 × PCIE0 +
ADC1D
PCINT0 × PCIE0 +
ADC0D
DIEOE
ADC3D
ADC2D
DIEOV
DI
PCINT3 × PCIE0
PCINT3 INPUT
ADC3 INPUT
PCINT2 × PCIE0
PCINT2 INPUT
ADC2 INPUT
PCINT1 × PCIE0
PCINT1 INPUT
ADC1 INPUT
PCINT0 × PCIE0
PCINT0 INPUT
ADC0 INPUT
AIO
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14.3.2 Alternate Functions of Port B
The port B pins with alternate functions are shown in Table 14-6.
Table 14-6. Port B Pins Alternate Functions
Port Pin
Alternate Functions
SCK (SPI bus master clock input)
PB7
OC3B (Timer/Counter 3 output compare match B output)
PCINT15 (pin change interrupt 15)
MISO (SPI bus master input/slave output)
OC3A (Timer/Counter 3 output compare match A output)
PCINT14 (pin change interrupt 14)
PB6
PB5
PB4
PB3
PB2
PB1
PB0
MOSI (SPI bus master output/slave input)
ICP3 (Timer/Counter3 input capture trigger)
PCINT13 (pin change interrupt 13)
SS (SPI slave select input)
OC0B (Timer/Counter 0 output compare match B output)
PCINT12 (pin change interrupt 12)
AIN1 (analog comparator negative input)
OC0A (Timer/Counter 0 output compare match A output)
PCINT11 (pin change interrupt 11)
AIN0 (analog comparator positive input)
INT2 (external interrupt 2 input)
PCINT10 (pin change interrupt 10)
T1 (Timer/Counter 1 external counter input)
CLKO (divided system clock output)
PCINT9 (pin change interrupt 9)
T0 (Timer/Counter 0 external counter input)
XCK0 (USART0 external clock input/output)
PCINT8 (pin change interrupt 8)
The alternate pin configuration is as follows:
• SCK/OC3B/PCINT15 – Port B, Bit 7
SCK: Master clock output, slave clock input pin for SPI channel. When the SPI is enabled as a slave, this pin is configured as
an input regardless of the setting of DDB7. When the SPI0 is enabled as a master, the data direction of this pin is controlled
by DDB7. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB7 bit.
OC3B, output compare match B output: The PB7 pin can serve as an external output for the Timer/Counter3 output
compare. The pin has to be configured as an output (DDB7 set “one”) to serve this function. The OC3B pin is also the output
pin for the PWM mode timer function.
PCINT15, pin change interrupt source 15: The PB7 pin can serve as an external interrupt source.
• MISO/OC3A/PCINT14 – Port B, Bit 6
MISO: Master data input, slave data output pin for SPI channel. When the SPI is enabled as a master, this pin is configured
as an input regardless of the setting of DDB6. When the SPI is enabled as a slave, the data direction of this pin is controlled
by DDB6. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB6 bit.
OC3A, output compare match A output: The PB6 pin can serve as an external output for the Timer/Counter0 output
compare. The pin has to be configured as an output (DDB6 set “one”) to serve this function. The OC3A pin is also the output
pin for the PWM mode timer function.
PCINT14, pin change interrupt source 14: The PB6 pin can serve as an external interrupt source.
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• MOSI/ICP3/PCINT13 – Port B, Bit 5
MOSI: SPI master data output, slave data input for SPI channel. When the SPI is enabled as a slave, this pin is configured
as an input regardless of the setting of DDB5. When the SPI is enabled as a master, the data direction of this pin is
controlled by DDB5. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB5 bit.
ICP3, input capture pin 3: The PB5 pin can act as an input capture pin for Timer/Counter3.
PCINT13, pin change interrupt source 13: The PB5 pin can serve as an external interrupt source.
• SS/OC0B/PCINT12 – Port B, Bit 4
SS: Slave port select input. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of
DDB4. As a slave, the SPI is activated when this pin is driven low. When the SPI is enabled as a master, the data direction
of this pin is controlled by DDB4. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB4 bit.
OC0B, output compare match B output: The PB4 pin can serve as an external output for the Timer/Counter0 output
compare. The pin has to be configured as an output (DDB4 set “one”) to serve this function. The OC0B pin is also the output
pin for the PWM mode timer function.
PCINT12, pin change interrupt source 12: The PB4 pin can serve as an external interrupt source.
• AIN1/OC0A/PCINT11, Bit 3
AIN1, analog comparator negative input. This pin is directly connected to the negative input of the analog comparator.
OC0A, output compare match A output: The PB3 pin can serve as an external output for the Timer/Counter0 output
compare. The pin has to be configured as an output (DDB3 set “one”) to serve this function. The OC0A pin is also the output
pin for the PWM mode timer function.
PCINT11, pin change interrupt source 11: The PB3 pin can serve as an external interrupt source.
• AIN0/INT2/PCINT10, Bit 2
AIN0, analog comparator positive input. This pin is directly connected to the positive input of the analog comparator.
INT2, external interrupt source 2. The PB2 pin can serve as an external interrupt source to the MCU.
PCINT10, pin change interrupt source 10: The PB2 pin can serve as an external interrupt source.
• T1/CLKO/PCINT9, Bit 1
T1, Timer/Counter1 counter source.
CLKO, divided system clock: The divided system clock can be output on the PB1 pin. The divided system clock will be output
if the CKOUT fuse is programmed, regardless of the PORTB1 and DDB1 settings. It will also be output during reset.
PCINT9, pin change interrupt source 9: The PB1 pin can serve as an external interrupt source.
• T0/XCK0/PCINT8, Bit 0
T0, Timer/Counter0 counter source.
XCK0, USART0 external clock. The data direction register (DDB0) controls whether the clock is output (DDD0 set “one”) or
input (DDD0 cleared). The XCK0 pin is active only when the USART0 operates in synchronous mode.
PCINT8, pin change interrupt source 8: The PB0 pin can serve as an external interrupt source.
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Table 14-7 and Table 14-8 relate the alternate functions of port B to the overriding signals shown in Figure 14-5 on page 62.
SPI MSTR INPUT and SPI SLAVE OUTPUT constitute the MISO signal, while MOSI is divided into SPI MSTR OUTPUT and
SPI SLAVE INPUT.
Table 14-7. Overriding Signals for Alternate Functions in PB7:PB4
Signal Name
PUOE
PB7/SCK/PCINT15
SPE × MSTR
PORTB7 × PUD
SPE × MSTR
0
PB6/MISO/PCINT14
SPE × MSTR
PORTB14 × PUD
SPE × MSTR
0
PB5/MOSI/PCINT13
SPE × MSTR
PORTB13 × PUD
SPE × MSTR
0
PB4/SS/OC0B/PCINT12
SPE × MSTR
PORTB12 × PUD
SPE × MSTR
0
PUOV
DDOE
DDOV
PVOE
SPE × MSTR
SCK OUTPUT
PCINT15 × PCIE1
1
SPE × MSTR
SPI SLAVE OUTPUT
PCINT14 × PCIE1
1
SPE × MSTR
SPI MSTR OUTPUT
PCINT13 × PCIE1
1
OC0A ENABLE
OC0A
PVOV
DIEOE
DIEOV
PCINT12 × PCIE1
1
SCK INPUT
PCINT17 INPUT
SPI MSTR INPUT
PCINT14 INPUT
SPI SLAVE INPUT
PCINT13 INPUT
SPI SS
PCINT12 INPUT
DI
AIO
–
–
–
–
Table 14-8. Overriding Signals for Alternate Functions in PB3:PB0
Signal Name PB3/AIN1/OC0B/PCINT11 PB2/AIN0/INT2/PCINT10 PB1/T1/CLKO/PCINT9 PB0/T0/XCK/PCINT8
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
CKOUT
CKOUT
CKOUT
CLK I/O
0
OC0B ENABLE
OC0B
INT2 ENABLE
PCINT10 × PCIE1
DIEOE
DIEOV
DI
PCINT11 × PCIE1
1
PCINT9 × PCIE1
PCINT8 × PCIE1
1
1
1
INT2 INPUT
PCINT10 INPUT
T1 INPUT
PCINT9 INPUT
T0 INPUT
PCINT8 INPUT
PCINT11 INPUT
AIN1 INPUT
AIO
AIN0 INPUT
–
–
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
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14.3.3 Alternate Functions of Port C
The port C pins with alternate functions are shown in Table 14-9.
Table 14-9. Port C Pins Alternate Functions
Port Pin
Alternate Function
TOSC2 (timer oscillator pin 2)
PCINT23 (pin change interrupt 23)
PC7
TOSC1 (timer oscillator pin 1)
PCINT22 (pin change interrupt 22)
PC6
PC5
PC4
PC3
PC2
PC1
PC0
TDI (JTAG test data input)
PCINT21 (pin change interrupt 21)
TDO (JTAG test data output)
PCINT20 (pin change interrupt 20)
TMS (JTAG test mode select)
PCINT19 (pin change interrupt 19)
TCK (JTAG test clock)
PCINT18 (pin change interrupt 18)
SDA (2-wire serial bus data input/output line)
PCINT17 (pin change interrupt 17)
SCL (2-wire serial bus clock line)
PCINT16 (pin change interrupt 16)
• TOSC2/PCINT23 – Port C, Bit7
TOSC2, timer oscillator pin 2. The PC7 pin can serve as an external interrupt source to the MCU.
PCINT23, pin change interrupt source 23: The PC7 pin can serve as an external interrupt source.
• TOSC1/PCINT22 – Port C, Bit 6
TOSC1, timer oscillator pin 1. The PC6 pin can serve as an external interrupt source to the MCU.
PCINT22, pin change interrupt source 22: The PC6 pin can serve as an external interrupt source.
• TDI/PCINT21 – Port C, Bit 5
TDI, JTAG test data input.
PCINT21, pin change interrupt source 21: The PC5 pin can serve as an external interrupt source.
• TDO/PCINT20 – Port C, Bit 4
TDO, JTAG test data output.
PCINT20, pin change interrupt source 20: The PC4 pin can serve as an external interrupt source.
• TMS/PCINT19 – Port C, Bit 3
TMS, JTAG test mode select.
PCINT19, pin change interrupt source 19: The PC3 pin can serve as an external interrupt source.
• TCK/PCINT18 – Port C, Bit 2
TCK, JTAG test clock.
PCINT18, pin change interrupt source 18: The PC2 pin can serve as an external interrupt source.
• SDA/PCINT17 – Port C, Bit 1
SDA, 2-wire serial bus data input/output line.
PCINT17, pin change interrupt source 17: The PC1 pin can serve as an external interrupt source.
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• SCL/PCINT16 – Port C, Bit 0
SCL, 2-wire serial bus clock line.
PCINT16, pin change interrupt source 16: The PC0 pin can serve as an external interrupt source.
Table 14-10 and Table 14-11 relate the alternate functions of port C to the overriding signals shown in
Figure 14-5 on page 62.
Table 14-10. Overriding Signals for Alternate Functions in PC7:PC4
Signal Name PC7/TOSC2/PCINT23
PC6/TOSC1/PCINT22
PC5/TDI/PCINT21
PC4/TDO/PCINT20
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
AS2 × EXCLK
AS2
0
JTAGEN
JTAGEN
0
1
1
AS2 × EXCLK
AS2
0
JTAGEN
JTAGEN
0
0
0
0
0
0
SHIFT_IR + SHIFT_DR
JTAGEN
0
0
TDO
AS2 × EXCLK +
PCINT23 × PCIE2
AS2 +
PCINT22 × PCIE2
JTAGEN +
PCINT21 × PCIE2
JTAGEN +
PCINT20 × PCIE2
DIEOE
DIEOV
DI
AS2
EXCLK + AS2
JTAGEN
JTAGEN
PCINT23 INPUT
T/C2 OSC OUTPUT
PCINT22 INPUT
T/C2 OSC INPUT
PCINT21 INPUT
TDI INPUT
PCINT20 INPUT
–
AIO
Table 14-11. Overriding Signals for Alternate Functions in PC3:PC0
Signal Name PC3/TMS/PCINT19
PC2/TCK/PCINT18
PC1/SDA/PCINT17
TWEN
PC0/SCL/PCINT16
TWEN
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
JTAGEN
JTAGEN
1
1
PORTC1 × PUD
TWEN
PORTC0 × PUD
TWEN
JTAGEN
JTAGEN
0
0
0
0
0
0
0
0
TWEN
TWEN
SDA OUT
SCL OUT
JTAGEN +
PCINT19 × PCIE2
JTAGEN +
PCINT18 × PCIE2
DIEOE
PCINT17 × PCIE2
PCINT16 × PCIE2
DIEOV
DI
JTAGEN
JTAGEN
1
1
PCINT19 INPUT
TMS INPUT
PCINT18 INPUT
TCK INPUT
PCINT17 INPUT
SDA INPUT
PCINT16 INPUT
SCL INPUT
AIO
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14.3.4 Alternate Functions of Port D
The port D pins with alternate functions are shown in Table 14-12.
Table 14-12. Port D Pins Alternate Functions
Port Pin
Alternate Function
OC2A (Timer/Counter2 output compare match A output)
PCINT31 (pin change interrupt 31)
PD7
ICP1 (Timer/Counter1 input capture trigger)
OC2B (Timer/Counter2 output compare match B output)
PCINT30 (pin change interrupt 30)
PD6
PD5
PD4
OC1A (Timer/Counter1 output compare match A output)
PCINT29 (pin change interrupt 29)
OC1B (Timer/Counter1 output compare match B output)
XCK1 (USART1 external clock input/output)
PCINT28 (pin change interrupt 28)
INT1 (external interrupt1 input)
TXD1 (USART1 transmit pin)
PCINT27 (pin change interrupt 27)
PD3
INT0 (external interrupt0 input)
RXD1 (USART1 receive pin)
PCINT26 (pin change interrupt 26)
PD2
PD1
PD0
TXD0 (USART0 transmit pin)
PCINT25 (pin change interrupt 25)
RXD0 (USART0 receive pin)
PCINT24 (pin change interrupt 24)
T3 (Timer/Counter 3 external counter input)
The alternate pin configuration is as follows:
• OC2A/PCINT31 – Port D, Bit 7
OC2A, output compare match A output: The PD7 pin can serve as an external output for the Timer/Counter2 output
compare A. The pin has to be configured as an output (DDD7 set (one)) to serve this function. The OC2A pin is also the
output pin for the PWM mode timer function.
PCINT31, pin change interrupt source 31:The PD7 pin can serve as an external interrupt source.
• ICP1/OC2B/PCINT30 – Port D, Bit 6
ICP1, input capture pin 1: The PD6 pin can act as an input capture pin for Timer/Counter1.
OC2B, output compare match B output: The PD6 pin can serve as an external output for the Timer/Counter2 output
compare B. The pin has to be configured as an output (DDD6 set (one)) to serve this function. The OC2B pin is also the
output pin for the PWM mode timer function.
PCINT30, pin change interrupt source 30: The PD6 pin can serve as an external interrupt source.
• OC1A/PCINT29 – Port D, Bit 5
OC1A, output compare match A output: The PD5 pin can serve as an external output for the Timer/Counter1 output
compare A. The pin has to be configured as an output (DDD5 set (one)) to serve this function. The OC1A pin is also the
output pin for the PWM mode timer function.
PCINT29, pin change interrupt source 29: The PD5 pin can serve as an external interrupt source.
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• OC1B/XCK1/PCINT28 – Port D, Bit 4
OC1B, output compare match B output: The PB4 pin can serve as an external output for the Timer/Counter1 output
compare B. The pin has to be configured as an output (DDD4 set (one)) to serve this function. The OC1B pin is also the
output pin for the PWM mode timer function.
XCK1, USART1 external clock. The data direction register (DDB4) controls whether the clock is output (DDD4 set “one”) or
input (DDD4 cleared). The XCK4 pin is active only when the USART1 operates in synchronous mode.
PCINT28, pin change interrupt source 28: The PD4 pin can serve as an external interrupt source.
• INT1/TXD1/PCINT27 – Port D, Bit 3
INT1, external interrupt source 1. The PD3 pin can serve as an external interrupt source to the MCU.
TXD1, transmit data (Data output pin for the USART1). When the USART1 transmitter is enabled, this pin is configured as
an output regardless of the value of DDD3.
PCINT27, pin change interrupt source 27: The PD3 pin can serve as an external interrupt source.
• INT0/RXD1/PCINT26 – Port D, Bit 2
INT0, external interrupt source 0. The PD2 pin can serve as an external interrupt source to the MCU.
RXD1, RXD0, receive Data (data input pin for the USART1). When the USART1 receiver is enabled this pin is configured as
an input regardless of the value of DDD2. When the USART forces this pin to be an input, the pull-up can still be controlled
by the PORTD2 bit.
PCINT26, pin change interrupt source 26: The PD2 pin can serve as an external interrupt source.
• TXD0/PCINT25 – Port D, Bit 1
TXD0, transmit data (Data output pin for the USART0). When the USART0 transmitter is enabled, this pin is configured as
an output regardless of the value of DDD1.
PCINT25, pin change interrupt source 25: The PD1 pin can serve as an external interrupt source.
• RXD0/T3/PCINT24 – Port D, Bit 0
RXD0, receive data (Data input pin for the USART0). When the USART0 receiver is enabled this pin is configured as an
input regardless of the value of DDD0. When the USART forces this pin to be an input, the pull-up can still be controlled by
the PORTD0 bit.
T3, Timer/Counter3 counter source.
PCINT24, pin change interrupt source 24: The PD0 pin can serve as an external interrupt source.
Table 14-13 on page 72 and Table 14-14 on page 72 relate the alternate functions of Port D to the overriding signals shown
in Figure 14-5 on page 62.
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Table 14-13. Overriding Signals for Alternate Functions PD7:PD4
Signal Name PD7/OC2A/PCINT31 PD6/ICP1/OC2B/PCINT30 PD5/OC1A/PCINT29 PD4/OC1B/XCK1/PCINT28
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
DIEOE
DIEOV
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
OC2A ENABLE
OCA2A
OC2B ENABLE
OC1A ENABLE
OC1B ENABLE
OC2B
OC1A
OC1B
PCINT31 × PCIE3
1
PCINT30 × PCIE3
PCINT29 × PCIE3
PCINT28 × PCIE3
1
1
1
ICP1 INPUT
PCINT30 INPUT
DI
PCINT31 INPUT
–
PCINT29 INPUT
–
PCINT28 INPUT
–
AIO
–
Table 14-14. Overriding Signals for Alternate Functions in PD3:PD0(1)
Signal Name PD3/INT1/TXD1/PCINT27 PD2/INT0/RXD1/PCINT26 PD1/TXD0/PCINT25 PD0/RXD0/PCINT27
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
TXEN1
0
RXEN1
TXEN0
0
RXEN1
PORTD2 × PUD
PORTD0 × PUD
TXEN1
1
RXEN1
TXEN0
1
RXEN1
0
0
0
0
0
0
TXEN1
TXD1
TXEN0
TXD0
INT1 ENABLE
PCINT27 × PCIE3
INT2 ENABLE
PCINT26 × PCIE3
DIEOE
DIEOV
DI
PCINT25 × PCIE3
PCINT24 × PCIE3
1
1
1
1
INT1 INPUT
PCINT27 INPUT
INT0 INPUTRXD1
PCINT26 INPUT
PCINT25 INPUT
RXD0PCINT24 INPUT
AIO
–
–
–
–
Note:
1. When enabled, the 2-wire serial interface enables slew-rate controls on the output pins PD0 and PD1. This is
not shown in this table. In addition, spike filters are connected between the AIO outputs shown in the port
figure and the digital logic of the TWI module.
14.4 Register Description
14.4.1 MCUCR – MCU Control Register
Bit
7
6
BODS
R/W
0
5
BODSE
R/W
0
4
3
–
2
–
1
IVSEL
R/W
0
0
IVCE
R/W
0
0x35 (0x55)
Read/Write
Initial Value
JTD
R/W
0
PUD
R/W
0
MCUCR
R
0
R
0
• Bit 4 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and PORTxn registers are
configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See Section 14.2.1 “Configuring the Pin” on page 59 for more
details about this feature.
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14.4.2 PORTA – Port A Data Register
Bit
7
6
5
4
3
2
1
0
0x02 (0x22) PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
14.4.3 DDRA – Port A Data Direction Register
Bit
7
DDA7
R/W
0
6
DDA6
R/W
0
5
DDA5
R/W
0
4
DDA4
R/W
0
3
DDA3
R/W
0
2
DDA2
R/W
0
1
DDA1
R/W
0
0
DDA0
R/W
0
0x01 (0x21)
Read/Write
Initial Value
DDRA
14.4.4 PINA – Port A Input Pins Address
Bit
7
6
5
4
3
2
1
0
0x00 (0x20)
Read/Write
Initial Value
PINA7
R/W
N/A
PINA6
R/W
N/A
PINA5
R/W
N/A
PINA4
R/W
N/A
PINA3
R/W
N/A
PINA2
R/W
N/A
PINA1
R/W
N/A
PINA0
R/W
N/A
PINA
14.4.5 PORTB – Port B Data Register
Bit
7
6
5
4
3
2
1
0
0x05 (0x25) PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
14.4.6 DDRB – Port B Data Direction Register
Bit
7
DDB7
R/W
0
6
DDB6
R/W
0
5
DDB5
R/W
0
4
DDB4
R/W
0
3
DDB3
R/W
0
2
DDB2
R/W
0
1
DDB1
R/W
0
0
DDB0
R/W
0
0x04 (0x24)
Read/Write
Initial Value
DDRB
14.4.7 PINB – Port B Input Pins Address
Bit
7
6
5
4
3
2
1
0
0x03 (0x23)
Read/Write
Initial Value
PINB7
R/W
N/A
PINB6
R/W
N/A
PINB5
R/W
N/A
PINB4
R/W
N/A
PINB3
R/W
N/A
PINB2
R/W
N/A
PINB1
R/W
N/A
PINB0
R/W
N/A
PINB
14.4.8 PORTC – Port C Data Register
Bit
7
6
5
4
3
2
1
0
0x08 (0x28) PORTC7 PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 PORTC
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
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14.4.9 DDRC – Port C Data Direction Register
Bit
7
DDC7
R/W
0
6
DDC6
R/W
0
5
DDC5
R/W
0
4
DDC4
R/W
0
3
DDC3
R/W
0
2
DDC2
R/W
0
1
DDC1
R/W
0
0
DDC0
R/W
0
0x07 (0x27)
Read/Write
Initial Value
DDRC
14.4.10 PINC – Port C Input Pins Address
Bit
7
6
5
4
3
2
1
0
0x06 (0x26)
Read/Write
Initial Value
PINC7
R/W
N/A
PINC6
R/W
N/A
PINC5
R/W
N/A
PINC4
R/W
N/A
PINC3
R/W
N/A
PINC2
R/W
N/A
PINC1
R/W
N/A
PINC0
R/W
N/A
PINC
14.4.11 PORTD – Port D Data Register
Bit
7
6
5
4
3
2
1
0
0x0B (0x2B) PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 PORTD
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
14.4.12 DDRD – Port D Data Direction Register
Bit
7
DDD7
R/W
0
6
DDD6
R/W
0
5
DDD5
R/W
0
4
DDD4
R/W
0
3
DDD3
R/W
0
2
DDD2
R/W
0
1
DDD1
R/W
0
0
DDD0
R/W
0
0x0A (0x2A)
Read/Write
Initial Value
DDRD
14.4.13 PIND – Port D Input Pins Address
Bit
7
6
5
4
3
2
1
0
0x09 (0x29)
Read/Write
Initial Value
PIND7
R/W
N/A
PIND6
R/W
N/A
PIND5
R/W
N/A
PIND4
R/W
N/A
PIND3
R/W
N/A
PIND2
R/W
N/A
PIND1
R/W
N/A
PIND0
R/W
N/A
PIND
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15. 8-bit Timer/Counter0 with PWM
15.1 Features
●
●
●
●
●
●
●
Two independent output compare units
Double buffered output compare registers
Clear timer on compare match (auto reload)
Glitch free, phase correct pulse width modulator (PWM)
Variable PWM period
Frequency generator
Three independent interrupt sources (TOV0, OCF0A, and OCF0B)
15.2 Overview
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent output compare units, and with
PWM support. It allows accurate program execution timing (event management) and wave generation.
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 15-1. For the actual placement of I/O pins, see
Section 1. “Pin Configurations” on page 3. CPU accessible I/O registers, including I/O bits and I/O pins, are shown in bold.
The device-specific I/O register and bit locations are listed in the Section 15.9 “Register Description” on page 85.
Figure 15-1. 8-bit Timer/Counter Block Diagram
TOVn (Int. Req.)
Count
Clock Select
Clear
Direction
Control Logic
Edge
Detector
Tn
clkTn
(from Prescaler)
TOP
BOTTOM
Timer/Counter
TCNTn
=
= 0
OCnA (Int. Req.)
Waveform
Generation
=
OCnA
OCRnA
Fixed
TOP
Value
OCnB (Int. Req.)
Waveform
Generation
=
OCnB
OCRnB
TCCRnA
TCCRnB
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15.2.1 Registers
The Timer/Counter (TCNT0) and output compare registers (OCR0A and OCR0B) are 8-bit registers. Interrupt request
(abbreviated to int.req. in the figure) signals are all visible in the timer interrupt flag register (TIFR0). All interrupts are
individually masked with the timer interrupt mask register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on the T0 pin. The clock select
logic block controls which clock source and edge the Timer/Counter uses to increment (or decrement) its value. The
Timer/Counter is inactive when no clock source is selected. The output from the clock select logic is referred to as the timer
clock (clkT0).
The double buffered output compare registers (OCR0A and OCR0B) are compared with the Timer/Counter value at all
times. The result of the compare can be used by the waveform generator to generate a PWM or variable frequency output on
the output compare pins (OC0A and OC0B). Section 15.5 “Output Compare Unit” on page 77 for details. The compare match
event will also set the compare flag (OCF0A or OCF0B) which can be used to generate an output compare interrupt request.
15.2.2 Definitions
Many register and bit references in this section are written in general form. A lower case “n” replaces the Timer/Counter
number, in this case 0. A lower case “x” replaces the output compare unit, in this case compare unit A or compare unit B.
However, when using the register or bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing
Timer/Counter0 counter value and so on.
The definitions in Table 15-1 are also used extensively throughout the document.
Table 15-1. Definitions
Parameter
BOTTOM
MAX
Definition
The counter reaches the BOTTOM when it becomes 0x00.
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The
TOP value can be assigned to be the fixed value 0xFF (MAX) or the value stored in the OCR0A register.
The assignment is dependent on the mode of operation.
TOP
15.3 Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the clock
select logic which is controlled by the clock select (CS02:0) bits located in the Timer/Counter control register (TCCR0B). For
details on clock sources and prescaler, see Section 17.10 “Timer/Counter Prescaler” on page 131.
15.4 Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 15-2 shows a block diagram
of the counter and its surroundings.
Figure 15-2. Counter Unit Block Diagram
TOVn
(Int. Req.)
DATA BUS
Clock Select
count
Edge
Tn
clkTn
Detector
clear
TCNTn
Control Logic
direction
(from Prescaler)
bottom
top
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Signal description (internal signals):
count
direction
clear
Increment or decrement TCNT0 by 1.
Select between increment and decrement.
Clear TCNT0 (set all bits to zero).
clkTn
Timer/Counter clock, referred to as clkT0 in the following.
Signalize that TCNT0 has reached maximum value.
Signalize that TCNT0 has reached minimum value (zero).
top
bottom
Depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT0).
clkT0 can be generated from an external or internal clock source, selected by the clock select bits (CS02:0). When no clock
source is selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of
whether clkT0 is present or not. A CPU write overrides (has priority over) all counter clear or count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the Timer/Counter control
register (TCCR0A) and the WGM02 bit located in the Timer/Counter control register B (TCCR0B). There are close
connections between how the counter behaves (counts) and how waveforms are generated on the output compare outputs
OC0A and OC0B. For more details about advanced counting sequences and waveform generation, see Section 15.7
“Modes of Operation” on page 79.
The Timer/Counter overflow flag (TOV0) is set according to the mode of operation selected by the WGM02:0 bits. TOV0 can
be used for generating a CPU interrupt.
15.5 Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the output compare registers (OCR0A and OCR0B). Whenever
TCNT0 equals OCR0A or OCR0B, the comparator signals a match. A match will set the output compare flag (OCF0A or
OCF0B) at the next timer clock cycle. If the corresponding interrupt is enabled, the output compare flag generates an output
compare interrupt. The output compare flag is automatically cleared when the interrupt is executed. Alternatively, the flag
can be cleared by software by writing a logical one to its I/O bit location. The waveform generator uses the match signal to
generate an output according to operating mode set by the WGM02:0 bits and compare output mode (COM0x1:0) bits. The
max and bottom signals are used by the waveform generator for handling the special cases of the extreme values in some
modes of operation (Section 15.7 “Modes of Operation” on page 79).
Figure 15-3 shows a block diagram of the output compare unit.
Figure 15-3. Output Compare Unit, Block Diagram
DATA BUS
OCRnx
TCNTn
= (8-bit Comparator)
OCFnx (Int. Req.)
OCnx
top
bottom
FOCn
Waveform Generator
WGMn1:0
COMnX1:0
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The OCR0x registers are double buffered when using any of the pulse width modulation (PWM) modes. For the normal and
clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the
update of the OCR0x compare registers to either top or bottom of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR0x register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has
access to the OCR0x buffer register, and if double buffering is disabled the CPU will access the OCR0x directly.
15.5.1 Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the force
output compare (FOC0x) bit. Forcing compare match will not set the OCF0x flag or reload/clear the timer, but the OC0x pin
will be updated as if a real compare match had occurred (the COM0x1:0 bits settings define whether the OC0x pin is set,
cleared or toggled).
15.5.2 Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0 register will block any compare match that occur in the next timer clock cycle, even
when the timer is stopped. This feature allows OCR0x to be initialized to the same value as TCNT0 without triggering an
interrupt when the Timer/Counter clock is enabled.
15.5.3 Using the Output Compare Unit
Since writing TCNT0 in any mode of operation will block all compare matches for one timer clock cycle, there are risks
involved when changing TCNT0 when using the output compare unit, independently of whether the Timer/Counter is running
or not. If the value written to TCNT0 equals the OCR0x value, the compare match will be missed, resulting in incorrect
waveform generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is down-counting.
The setup of the OC0x should be performed before setting the data direction register for the port pin to output. The easiest
way of setting the OC0x value is to use the force output compare (FOC0x) strobe bits in normal mode. The OC0x registers
keep their values even when changing between waveform generation modes.
Be aware that the COM0x1:0 bits are not double buffered together with the compare value. Changing the COM0x1:0 bits will
take effect immediately.
15.6 Compare Match Output Unit
The compare output mode (COM0x1:0) bits have two functions. The waveform generator uses the COM0x1:0 bits for
defining the output compare (OC0x) state at the next compare match. Also, the COM0x1:0 bits control the OC0x pin output
source. Figure 15-4 on page 79 shows a simplified schematic of the logic affected by the COM0x1:0 bit setting.
The I/O registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O port control registers
(DDR and PORT) that are affected by the COM0x1:0 bits are shown. When referring to the OC0x state, the reference is for
the internal OC0x register, not the OC0x pin. If a system reset occur, the OC0x register is reset to “0”.
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Figure 15-4. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCn
Waveform
Generator
D
D
Q
Q
1
0
OCnx
Pin
OCnx
PORT
D
Q
DDR
clkI/O
The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform Generator if either of the
COM0x1:0 bits are set. However, the OC0x pin direction (input or output) is still controlled by the data direction register
(DDR) for the port pin. The data direction register bit for the OC0x pin (DDR_OC0x) must be set as output before the OC0x
value is visible on the pin. The port override function is independent of the waveform generation mode.
The design of the output compare pin logic allows initialization of the OC0x state before the output is enabled. Note that
some COM0x1:0 bit settings are reserved for certain modes of operation. See Section 15.9 “Register Description” on page
85.
15.6.1 Compare Output Mode and Waveform Generation
The waveform generator uses the COM0x1:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the
COM0x1:0 = 0 tells the waveform generator that no action on the OC0x register is to be performed on the next compare
match. For compare output actions in the non-PWM modes refer to Table 15-2 on page 85. For fast PWM mode, refer to
Table 15-3 on page 85, and for phase correct PWM refer to Table 15-4 on page 85.
A change of the COM0x1:0 bits state will have effect at the first compare match after the bits are written. For non-PWM
modes, the action can be forced to have immediate effect by using the FOC0x strobe bits.
15.7 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the output compare pins, is defined by the combination of
the waveform generation mode (WGM02:0) and compare output mode (COM0x1:0) bits. The compare output mode bits do
not affect the counting sequence, while the waveform generation mode bits do. The COM0x1:0 bits control whether the
PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM0x1:0 bits
control whether the output should be set, cleared, or toggled at a compare match (see Section 16.8 “Compare Match Output
Unit” on page 100). For detailed timing information see Section 15.8 “Timer/Counter Timing Diagrams” on page 83.
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15.7.1 Normal Mode
The simplest mode of operation is the normal mode (WGM02:0 = 0). In this mode the counting direction is always up
(incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 8-bit value
(TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the Timer/Counter overflow flag (TOV0) will be
set in the same timer clock cycle as the TCNT0 becomes zero. The TOV0 flag in this case behaves like a ninth bit, except
that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV0 flag,
the timer resolution can be increased by software. There are no special cases to consider in the normal mode, a new counter
value can be written anytime.
The output compare unit can be used to generate interrupts at some given time. Using the output compare to generate
waveforms in normal mode is not recommended, since this will occupy too much of the CPU time.
15.7.2 Clear Timer on Compare Match (CTC) Mode
In clear timer on compare or CTC mode (WGM02:0 = 2), the OCR0A register is used to manipulate the counter resolution. In
CTC mode the counter is cleared to zero when the counter value (TCNT0) matches the OCR0A. The OCR0A defines the top
value for the counter, hence also its resolution. This mode allows greater control of the compare match output frequency. It
also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 15-5. The counter value (TCNT0) increases until a compare match
occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared.
Figure 15-5. CTC Mode, Timing Diagram
OCnx Interrupt
Flag Set
TCNTn
OCnx
(COMnx1:0 = 1)
(Toggle)
1
2
3
4
Period
An interrupt can be generated each time the counter value reaches the TOP value by using the OCF0A flag. If the interrupt
is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing TOP to a value close to
BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does
not have the double buffering feature. If the new value written to OCR0A is lower than the current value of TCNT0, the
counter will miss the compare match. The counter will then have to count to its maximum value (0xFF) and wrap around
starting at 0x00 before the compare match can occur.
For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logical level on each compare
match by setting the compare output mode bits to toggle mode (COM0A1:0 = 1). The OC0A value will not be visible on the
port pin unless the data direction for the pin is set to output. The waveform generated will have a maximum frequency of fOC0
= fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following equation:
f
clk_I/O
------------------------------------------------
f
=
OCnx
2 N (1 + OCRnx)
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the normal mode of operation, the TOV0 flag is set in the same timer clock cycle that the counter counts from MAX to
0x00.
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15.7.3 Fast PWM Mode
The fast pulse width modulation or fast PWM mode (WGM02:0 = 3 or 7) provides a high frequency PWM waveform
generation option. The fast PWM differs from the other PWM option by its single-slope operation. The counter counts from
BOTTOM to TOP then restarts from BOTTOM. TOP is defined as 0xFF when WGM2:0 = 3, and OCR0A when WGM2:0 = 7.
In non-inverting compare output mode, the output compare (OC0x) is cleared on the compare match between TCNT0 and
OCR0x, and set at BOTTOM. In inverting compare output mode, the output is set on compare match and cleared at
BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high as the
phase correct PWM mode that use dual-slope operation. This high frequency makes the fast PWM mode well suited for
power regulation, rectification, and DAC applications. High frequency allows physically small sized external components
(coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value. The counter is then cleared at
the following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure 15-6. The TCNT0 value is in
the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare matches between OCR0x
and TCNT0.
Figure 15-6. Fast PWM Mode, Timing Diagram
OCRnx Interrupt
Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
TCNTn
(COMnx1:0 = 2)
OCnx
OCnx
(COMnx1:0 = 3)
1
2
3
4
5
6
7
Period
The Timer/Counter overflow flag (TOV0) is set each time the counter reaches TOP. If the interrupt is enabled, the interrupt
handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins. Setting the COM0x1:0 bits to
two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM0x1:0 to three:
Setting the COM0A1:0 bits to one allows the OC0A pin to toggle on compare matches if the WGM02 bit is set. This option is
not available for the OC0B pin (See Table 15-3 on page 85). The actual OC0x value will only be visible on the port pin if the
data direction for the port pin is set as output. The PWM waveform is generated by setting (or clearing) the OC0x register at
the compare match between OCR0x and TCNT0, and clearing (or setting) the OC0x register at the timer clock cycle the
counter is cleared (changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f
clk_I/O
----------------
f
=
OCnxPWM
N 256
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A register represents special cases when generating a PWM waveform output in the fast
PWM mode. If the OCR0A is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle.
Setting the OCR0A equal to MAX will result in a constantly high or low output (depending on the polarity of the output set by
the COM0A1:0 bits.)
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A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0x to toggle its logical
level on each compare match (COM0x1:0 = 1). The waveform generated will have a maximum frequency of fOC0 = fclk_I/O/2
when OCR0A is set to zero. This feature is similar to the OC0A toggle in CTC mode, except the double buffer feature of the
output compare unit is enabled in the fast PWM mode.
15.7.4 Phase Correct PWM Mode
The phase correct PWM mode (WGM02:0 = 1 or 5) provides a high resolution phase correct PWM waveform generation
option. The phase correct PWM mode is based on a dual-slope operation. The counter counts repeatedly from BOTTOM to
TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1, and OCR0A when WGM2:0 = 5.
In non-inverting compare output mode, the output compare (OC0x) is cleared on the compare match between TCNT0 and
OCR0x while upcounting, and set on the compare match while down-counting. In inverting output compare mode, the
operation is inverted. The dual-slope operation has lower maximum operation frequency than single slope operation.
However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP. When the counter reaches
TOP, it changes the count direction. The TCNT0 value will be equal to TOP for one timer clock cycle. The timing diagram for
the phase correct PWM mode is shown on Figure 15-7. The TCNT0 value is in the timing diagram shown as a histogram for
illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line
marks on the TCNT0 slopes represent compare matches between OCR0x and TCNT0.
Figure 15-7. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt
Flag Set
OCRnx Update
TOVn Interrupt
Flag Set
TCNTn
(COMnx1:0 = 2)
OCnx
OCnx
(COMnx1:0 = 3)
1
2
3
Period
The Timer/Counter overflow flag (TOV0) is set each time the counter reaches BOTTOM. The interrupt flag can be used to
generate an interrupt each time the counter reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins. Setting the
COM0x1:0 bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by setting the
COM0x1:0 to three: Setting the COM0A0 bits to one allows the OC0A pin to toggle on compare matches if the WGM02 bit is
set. This option is not available for the OC0B pin (See Table 15-4 on page 85). The actual OC0x value will only be visible on
the port pin if the data direction for the port pin is set as output.
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The PWM waveform is generated by clearing (or setting) the OC0x register at the compare match between OCR0x and
TCNT0 when the counter increments, and setting (or clearing) the OC0x register at compare match between OCR0x and
TCNT0 when the counter decrements. The PWM frequency for the output when using phase correct PWM can be calculated
by the following equation:
f
clk_I/O
----------------
f
=
OCnxPCPWM
N 510
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A register represent special cases when generating a PWM waveform output in the phase
correct PWM mode. If the OCR0A is set equal to BOTTOM, the output will be continuously low and if set equal to MAX the
output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic
values.
At the very start of period 2 in Figure 15-7 on page 82 OCnx has a transition from high to low even though there is no
compare match. The point of this transition is to guarantee symmetry around BOTTOM. There are two cases that give a
transition without compare match.
●
OCR0A changes its value from MAX, like in Figure 15-7 on page 82. When the OCR0A value is MAX the OCn pin
value is the same as the result of a down-counting compare match. To ensure symmetry around BOTTOM the OCn
value at MAX must correspond to the result of an up-counting compare match.
●
The timer starts counting from a value higher than the one in OCR0A, and for that reason misses the compare match
and hence the OCn change that would have happened on the way up.
15.8 Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a clock enable signal in the
following figures. The figures include information on when interrupt flags are set. Figure 15-8 contains timing data for basic
Timer/Counter operation. The figure shows the count sequence close to the MAX value in all modes other than phase
correct PWM mode.
Figure 15-8. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O/1)
TCNTn
TOVn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
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Figure 15-9 shows the same timing data, but with the prescaler enabled.
Figure 15-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
TOVn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
Figure 15-10 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC mode and PWM mode, where
OCR0A is TOP.
Figure 15-10.Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx
OCFnx
OCRnx Value
Figure 15-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast PWM mode where OCR0A is
TOP.
Figure 15-11.Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
(CTC)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
OCRnx
TOP
OCFnx
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15.9 Register Description
15.9.1 TCCR0A – Timer/Counter Control Register A
Bit
7
6
5
4
3
–
2
–
1
0
0x24 (0x44) COM0A1 COM0A0 COM0B1 COM0B0
WGM01 WGM00 TCCR0A
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R
0
R
0
R/W
0
R/W
0
• Bits 7:6 – COM0A1:0: Compare Match Output A Mode
These bits control the output compare pin (OC0A) behavior. If one or both of the COM0A1:0 bits are set, the OC0A output
overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)
bit corresponding to the OC0A pin must be set in order to enable the output driver.
When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the WGM02:0 bit setting. Table 15-2
shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to a normal or CTC mode (non-PWM).
Table 15-2. Compare Output Mode, non-PWM Mode
COM0A1
COM0A0
Description
0
0
1
1
0
1
0
1
Normal port operation, OC0A disconnected.
Toggle OC0A on compare match
Clear OC0A on compare match
Set OC0A on compare match
Table 15-3 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM mode.
Table 15-3. Compare Output Mode, Fast PWM Mode(1)
COM0A1
COM0A0
Description
0
0
Normal port operation, OC0A disconnected.
WGM02 = 0: Normal port operation, OC0A disconnected.
WGM02 = 1: Toggle OC0A on compare match.
0
1
1
1
0
1
Clear OC0A on compare match, set OC0A at BOTTOM,
(non-inverting mode).
Set OC0A on compare match, clear OC0A at BOTTOM,
(inverting mode).
Note:
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the compare match is
ignored, but the set or clear is done at BOTTOM. See Section 15.7.3 “Fast PWM Mode” on page 81 for more
details.
Table 15-4 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 15-4. Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1
COM0A0
Description
0
0
Normal port operation, OC0A disconnected.
WGM02 = 0: Normal port operation, OC0A disconnected.
WGM02 = 1: Toggle OC0A on compare match.
0
1
1
1
0
1
Clear OC0A on compare match when up-counting. Set OC0A on compare match
when down-counting.
Set OC0A on compare match when up-counting. Clear OC0A on compare match
when down-counting.
Note:
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 15.7.4 “Phase Correct PWM Mode” on page 82 for
more details.
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• Bits 5:4 – COM0B1:0: Compare Match Output B Mode
These bits control the output compare pin (OC0B) behavior. If one or both of the COM0B1:0 bits are set, the OC0B output
overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)
bit corresponding to the OC0B pin must be set in order to enable the output driver.
When OC0B is connected to the pin, the function of the COM0B1:0 bits depends on the WGM02:0 bit setting.
Table 15-2 on page 85 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to a normal or CTC mode
(non-PWM).
Table 15-5. Compare Output Mode, non-PWM Mode
COM0B1
COM0B0
Description
0
0
1
1
0
1
0
1
Normal port operation, OC0B disconnected.
Toggle OC0B on compare match
Clear OC0B on compare match
Set OC0B on compare match
Table 15-6 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast PWM mode.
Table 15-6. Compare Output Mode, Fast PWM Mode(1)
COM0B1
COM0B0
Description
0
0
1
1
0
1
0
1
Normal port operation, OC0B disconnected.
Reserved
Clear OC0B on compare match, set OC0B at BOTTOM, (non-inverting mode).
Set OC0B on compare match, clear OC0B at BOTTOM, (inverting mode).
Note:
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the compare match is
ignored, but the set or clear is done atBOTTOM. See Section 15.7.3 “Fast PWM Mode” on page 81 for more
details.
Table 15-7 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 15-7. Compare Output Mode, Phase Correct PWM Mode(1)
COM0B1
COM0B0
Description
0
0
0
1
Normal port operation, OC0B disconnected.
Reserved
Clear OC0B on compare match when up-counting. Set OC0B on compare match
when down-counting.
1
1
0
1
Set OC0B on compare match when up-counting. Clear OC0B on compare match
when down-counting.
Note:
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 15.7.4 “Phase Correct PWM Mode” on page 82 for
more details.
• Bits 3:2 – Reserved
These bits are reserved bits in the ATmega164P-B/324P-B/644P-B and will always read as zero.
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• Bits 1:0 – WGM01:0: Waveform Generation Mode
Combined with the WGM02 bit found in the TCCR0B register, these bits control the counting sequence of the counter, the
source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 15-8. Modes of
operation supported by the Timer/Counter unit are: normal mode (counter), clear timer on compare match (CTC) mode, and
two types of pulse width modulation (PWM) modes (see Section 16.9 “Modes of Operation” on page 101).
Table 15-8. Waveform Generation Mode Bit Description
Timer/Counter Mode of
Mode WGM2 WGM1 WGM0
Operation
TOP
0xFF
0xFF
OCRA
0xFF
–
Update of OCRx at TOV Flag Set on(1)(2)
0
1
2
3
4
5
6
7
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Normal
Immediate
TOP
MAX
BOTTOM
MAX
PWM, phase correct
CTC
Immediate
BOTTOM
–
Fast PWM
MAX
Reserved
–
PWM, phase correct
Reserved
OCRA
–
TOP
BOTTOM
–
–
Fast PWM
OCRA
BOTTOM
TOP
Notes: 1. MAX
= 0xFF
2. BOTTOM = 0x00
15.9.2 TCCR0B – Timer/Counter Control Register B
Bit
7
FOC0A
W
6
FOC0B
W
5
–
4
–
3
WGM02
R/W
0
2
CS02
R/W
0
1
0
0x25 (0x45)
Read/Write
Initial Value
CS01
R/W
0
CS00
R/W
0
TCCR0B
R
0
R
0
0
0
• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR0B is written when operating
in PWM mode. When writing a logical one to the FOC0A bit, an immediate compare match is forced on the waveform
generation unit. The OC0A output is changed according to its COM0A1:0 bits setting. Note that the FOC0A bit is
implemented as a strobe. Therefore it is the value present in the COM0A1:0 bits that determines the effect of the forced
compare.
A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0A as TOP.
The FOC0A bit is always read as zero.
• Bit 6 – FOC0B: Force Output Compare B
The FOC0B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR0B is written when operating
in PWM mode. When writing a logical one to the FOC0B bit, an immediate compare match is forced on the waveform
generation unit. The OC0B output is changed according to its COM0B1:0 bits setting. Note that the FOC0B bit is
implemented as a strobe. Therefore it is the value present in the COM0B1:0 bits that determines the effect of the forced
compare.
A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0B as TOP.
The FOC0B bit is always read as zero.
• Bits 5:4 – Reserved
These bits are reserved and will always read as zero.
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• Bit 3 – WGM02: Waveform Generation Mode
See the description in the Section 15.9.1 “TCCR0A – Timer/Counter Control Register A” on page 85.
• Bits 2:0 – CS02:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter.
Table 15-9. Clock Select Bit Description
CS02
CS01
CS00
Description
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
No clock source (Timer/Counter stopped)
clkI/O/(no prescaling)
clkI/O/8 (from prescaler)
clkI/O/64 (from prescaler)
clkI/O/256 (from prescaler)
clkI/O/1024 (from prescaler)
External clock source on T0 pin. Clock on falling edge.
External clock source on T0 pin. Clock on rising edge.
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the counter even if the pin is
configured as an output. This feature allows software control of the counting.
15.9.3 TCNT0 – Timer/Counter Register
Bit
7
6
5
4
3
2
1
0
0x26 (0x46)
Read/Write
Initial Value
TCNT0[7:0]
R/W R/W
TCNT0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
0
The Timer/Counter register gives direct access, both for read and write operations, to the Timer/Counter unit 8-bit counter.
Writing to the TCNT0 register blocks (removes) the compare match on the following timer clock. Modifying the counter
(TCNT0) while the counter is running, introduces a risk of missing a compare match between TCNT0 and the OCR0x
registers.
15.9.4 OCR0A – Output Compare Register A
Bit
7
6
5
4
3
2
1
0
0x27 (0x47)
Read/Write
Initial Value
OCR0A[7:0]
R/W R/W
OCR0A
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
0
The output compare register A contains an 8-bit value that is continuously compared with the counter value (TCNT0). A
match can be used to generate an output compare interrupt, or to generate a waveform output on the OC0A pin.
15.9.5 OCR0B – Output Compare Register B
Bit
7
6
5
4
3
2
1
0
0x28 (0x48)
Read/Write
Initial Value
OCR0B[7:0]
R/W R/W
OCR0B
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
0
The output compare register B contains an 8-bit value that is continuously compared with the counter value (TCNT0). A
match can be used to generate an output compare interrupt, or to generate a waveform output on the OC0B pin.
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15.9.6 TIMSK0 – Timer/Counter Interrupt Mask Register
Bit
7
–
6
–
5
–
4
–
3
–
2
1
0
TOIE0
R/W
0
(0x6E)
OCIE0B OCIE0A
TIMSK0
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R
0
R/W
0
R/W
0
• Bits 7:3 – Reserved
These bits are reserved and will always read as zero.
• Bit 2 – OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable
When the OCIE0B bit is written to one, and the I-bit in the status register is set, the Timer/Counter compare match B interrupt
is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter occurs, i.e., when the OCF0B bit is
set in the Timer/Counter interrupt flag register – TIFR0.
• Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the status register is set, the Timer/Counter0 compare match A
interrupt is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter0 occurs, i.e., when the
OCF0A bit is set in the Timer/Counter 0 interrupt flag register – TIFR0.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the status register is set, the Timer/Counter0 overflow interrupt is
enabled. The corresponding interrupt is executed if an overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in
the Timer/Counter 0 interrupt flag register – TIFR0.
15.9.7 TIFR0 – Timer/Counter 0 Interrupt Flag Register
Bit
7
–
6
–
5
–
4
–
3
–
2
OCF0B
R/W
0
1
OCF0A
R/W
0
0
TOV0
R/W
0
0x15 (0x35)
Read/Write
Initial Value
TIFR0
R
0
R
0
R
0
R
0
R
0
• Bits 7:3 – Reserved
These bits are reserved and will always read as zero.
• Bit 2 – OCF0B: Timer/Counter 0 Output Compare B Match Flag
The OCF0B bit is set when a compare match occurs between the Timer/Counter and the data in OCR0B – output compare
register0 B. OCF0B is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively,
OCF0B is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0B (Timer/Counter compare B match
interrupt enable), and OCF0B are set, the Timer/Counter compare match interrupt is executed.
• Bit 1 – OCF0A: Timer/Counter 0 Output Compare A Match Flag
The OCF0A bit is set when a compare match occurs between the Timer/Counter0 and the data in OCR0A – output compare
register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0A
is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0A (Timer/Counter0 compare match interrupt
enable), and OCF0A are set, the Timer/Counter0 compare match interrupt is executed.
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, TOV0 is cleared by writing a logic one to the flag. When the
SREG I-bit, TOIE0 (Timer/Counter0 overflow interrupt enable), and TOV0 are set, the Timer/Counter0 overflow interrupt is
executed.
The setting of this flag is dependent of the WGM02:0 bit setting. Refer to Table 15-8 on page 87,
Section 15-8 “Waveform Generation Mode Bit Description” on page 87.
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16. 16-bit Timer/Counter1 and Timer/Counter3 with PWM
16.1 Features
●
●
●
●
●
●
●
●
●
●
●
True 16-bit design (i.e., allows 16-bit PWM)
Two independent output compare units
Double buffered output compare registers
One input capture unit
Input capture noise canceler
Clear timer on compare match (auto reload)
Glitch-free, phase correct pulse width modulator (PWM)
Variable PWM period
Frequency generator
External event counter
Four independent interrupt sources (TOV1, OCF1A, OCF1B, and ICF1)
16.2 Overview
The 16-bit Timer/Counter unit allows accurate program execution timing (event management), wave generation, and signal
timing measurement.
Most register and bit references in this section are written in general form. A lower case “n” replaces the Timer/Counter
number, and a lower case “x” replaces the output compare unit channel. However, when using the register or bit defines in a
program, the precise form must be used, i.e., TCNT1 for accessing Timer/Counter1 counter value and so on.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 16-1 on page 91. For the actual placement of I/O
pins, see Section 1. “Pin Configurations” on page 3. CPU accessible I/O registers, including I/O bits and I/O pins, are shown
in bold. The device-specific I/O register and bit locations are listed in the Section 16.11 “Register Description” on page 109.
The PRTIM1 bit in Section 10.12.3 “PRR0 – Power Reduction Register 0” on page 39 must be written to zero to enable
Timer/Counter1 module.
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Figure 16-1. 16-bit Timer/Counter Block Diagram(1)
TOVn (Int. Req.)
Clock Select
Count
Clear
Direction
Control Logic
Edge
Detector
Tn
clkTn
(from Prescaler)
TOP
BOTTOM
Timer/Counter
TCNTn
=
=
0
OCnA (Int. Req.)
Waveform
Generation
OCnA
OCnB
=
OCRnA
Fixed
TOP
Value
OCnB (Int. Req.)
Waveform
Generation
=
OCRnB
(From Analog
Comparator Output)
ICPn
ICFn (Int. Req.)
Edge
Detector
Noise
Canceler
ICRn
TCCRnA
TCCRnB
Note:
1. Refer to Figure 1-1 on page 3 and Section 14.3 “Alternate Port Functions” on page 62 for Timer/Counter1 pin
placement and description.
16.2.1 Registers
The Timer/Counter (TCNTn), output compare registers (OCRnA/B/C), and input capture register (ICRn) are all
16-bit registers. Special procedures must be followed when accessing the 16-bit registers. These procedures are described
in the section Section 16.3 “Accessing 16-bit Registers” on page 92. The Timer/Counter control registers (TCCRnA/B/C) are
8-bit registers and have no CPU access restrictions. Interrupt requests (abbreviated to int.req. in the figure) signals are all
visible in the timer interrupt flag register (TIFRn). All interrupts are individually masked with the timer interrupt mask register
(TIMSKn). TIFRn and TIMSKn are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on the Tn pin. The clock select
logic block controls which clock source and edge the Timer/Counter uses to increment (or decrement) its value. The
Timer/Counter is inactive when no clock source is selected. The output from the clock select logic is referred to as the timer
clock (clkTn).
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The double buffered output compare registers (OCRnA/B/C) are compared with the Timer/Counter value at all time. The
result of the compare can be used by the waveform generator to generate a PWM or variable frequency output on the output
compare pin (OCnA/B/C). Section 16.7 “Output Compare Units” on page 98. The compare match event will also set the
compare match flag (OCFnA/B/C) which can be used to generate an output compare interrupt request.
The input capture register can capture the Timer/Counter value at a given external (edge triggered) event on either the input
capture pin (ICPn) or on the analog comparator pins (Section 22. “AC - Analog Comparator” on page 204) The input capture
unit includes a digital filtering unit (noise canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be defined by either the OCRnA
register, the ICRn register, or by a set of fixed values. When using OCRnA as TOP value in a PWM mode, the OCRnA
register can not be used for generating a PWM output. However, the TOP value will in this case be double buffered allowing
the TOP value to be changed in run time. If a fixed TOP value is required, the ICRn register can be used as an alternative,
freeing the OCRnA to be used as PWM output.
16.2.2 Definitions
The following definitions are used extensively throughout the section:
Table 16-1. Definitions
Parameter
BOTTOM
MAX
Definition
The counter reaches the BOTTOM when it becomes 0x0000.
The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65535).
The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The TOP
value can be assigned to be one of the fixed values: 0x00FF, 0x01FF, or 0x03FF, or to the value stored in
the OCRnA or ICRn register. The assignment is dependent of the mode of operation.
TOP
16.3 Accessing 16-bit Registers
The TCNTn, OCRnA/B/C, and ICRn are 16-bit registers that can be accessed by the AVR® CPU via the 8-bit data bus. The
16-bit register must be byte accessed using two read or write operations. Each 16-bit timer has a single 8-bit register for
temporary storing of the high byte of the 16-bit access. The same temporary register is shared between all 16-bit registers
within each 16-bit timer. Accessing the low byte triggers the 16-bit read or write operation. When the low byte of a
16-bit register is written by the CPU, the high byte stored in the temporary register, and the low byte written are both copied
into the 16-bit register in the same clock cycle. When the low byte of a 16-bit register is read by the CPU, the high byte of the
16-bit register is copied into the temporary register in the same clock cycle as the low byte is read.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCRnA/B/C 16-bit registers does not
involve using the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low byte must be read before the
high byte.
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The following code examples show how to access the 16-bit timer registers assuming that no interrupts updates the
temporary register. The same principle can be used directly for accessing the OCRnA/B/C and ICRn registers. Note that
when using “C”, the compiler handles the 16-bit access.
Assembly Code Examples(1)
...
; Set TCNTn to 0x01FF
ldi
ldi
out
out
r17,0x01
r16,0xFF
TCNTnH,r17
TCNTnL,r16
; Read TCNTn into r17:r16
in
in
...
r16,TCNTnL
r17,TCNTnH
C Code Examples(1)
unsigned int i;
...
/* Set TCNTn to 0x01FF */
TCNTn = 0x1FF;
/* Read TCNTn into i */
i = TCNTn;
...
Note:
1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNTn value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt occurs between the two
instructions accessing the 16-bit register, and the interrupt code updates the temporary register by accessing the same or
any other of the 16-bit timer registers, then the result of the access outside the interrupt will be corrupted. Therefore, when
both the main code and the interrupt code update the temporary register, the main code must disable the interrupts during
the 16-bit access.
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The following code examples show how to do an atomic read of the TCNTn register contents. Reading any of the
OCRnA/B/C or ICRn registers can be done by using the same principle.
Assembly Code Example(1)
TIM16_ReadTCNTn:
; Save global interrupt flag
in
r18,SREG
; Disable interrupts
cli
; Read TCNTn into r17:r16
in
in
r16,TCNTnL
r17,TCNTnH
; Restore global interrupt flag
out
ret
SREG,r18
C Code Example(1)
unsigned int TIM16_ReadTCNTn( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNTn into i */
i = TCNTn;
/* Restore global interrupt flag */
SREG = sreg;
return i;
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNTn value in the r17:r16 register pair.
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The following code examples show how to do an atomic write of the TCNTn register contents. Writing any of the OCRnA/B/C
or ICRn registers can be done by using the same principle.
Assembly Code Example(1)
TIM16_WriteTCNTn:
; Save global interrupt flag
in
r18,SREG
; Disable interrupts
cli
; Set TCNTn to r17:r16
out
out
TCNTnH,r17
TCNTnL,r16
; Restore global interrupt flag
out
ret
SREG,r18
C Code Example(1)
void TIM16_WriteTCNTn(unsigned int i)
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNTn to i */
TCNTn = i;
/* Restore global interrupt flag */
SREG = sreg;
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNTn.
16.3.1 Reusing the Temporary High Byte Register
If writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte only
needs to be written once. However, note that the same rule of atomic operation described previously also applies in this
case.
16.4 Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the clock
select logic which is controlled by the clock select (CSn2:0) bits located in the Timer/Counter control register B (TCCRnB).
For details on clock sources and prescaler, see Section 17.10 “Timer/Counter Prescaler” on page 131.
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16.5 Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit. Figure 16-2 on page 96
shows a block diagram of the counter and its surroundings.
Figure 16-2. Counter Unit Block Diagram
DATA BUS (8-bit)
TOVn
(Int. Req.)
TEMP (8-bit)
Clock Select
Count
Edge
Tn
TCNTnH (8-bit)
TCNTnL (8-bit)
clkTn
Detector
Clear
Control Logic
Direction
TCNTnH (16-bit Counter)
(from Prescaler)
TOP
BOTTOM
Signal description (internal signals):
Count
Direction
Clear
Increment or decrement TCNTn by 1.
Select between increment and decrement.
Clear TCNTn (set all bits to zero).
Timer/Counter clock.
clkTn
TOP
Signalize that TCNTn has reached maximum value.
BOTTOM
Signalize that TCNTn has reached minimum value (zero).
The 16-bit counter is mapped into two 8-bit I/O memory locations: counter high (TCNTnH) containing the upper eight bits of
the counter, and counter low (TCNTnL) containing the lower eight bits. The TCNTnH register can only be indirectly accessed
by the CPU. When the CPU does an access to the TCNTnH I/O location, the CPU accesses the high byte temporary register
(TEMP). The temporary register is updated with the TCNTnH value when the TCNTnL is read, and TCNTnH is updated with
the temporary register value when TCNTnL is written. This allows the CPU to read or write the entire 16-bit counter value
within one clock cycle via the 8-bit data bus. It is important to notice that there are special cases of writing to the TCNTn
register when the counter is counting that will give unpredictable results. The special cases are described in the sections
where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkTn).
The clkTn can be generated from an external or internal clock source, selected by the clock select bits (CSn2:0). When no
clock source is selected (CSn2:0 = 0) the timer is stopped. However, the TCNTn value can be accessed by the CPU,
independent of whether clkTn is present or not. A CPU write overrides (has priority over) all counter clear or count
operations.
The counting sequence is determined by the setting of the waveform generation mode bits (WGMn3:0) located in the
Timer/Counter control registers A and B (TCCRnA and TCCRnB). There are close connections between how the counter
behaves (counts) and how waveforms are generated on the output compare outputs OCnx. For more details about
advanced counting sequences and waveform generation, see Section 16.9 “Modes of Operation” on page 101.
The Timer/Counter overflow flag (TOVn) is set according to the mode of operation selected by the WGMn3:0 bits. TOVn can
be used for generating a CPU interrupt.
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16.6 Input Capture Unit
The Timer/Counter incorporates an input capture unit that can capture external events and give them a time-stamp
indicating time of occurrence. The external signal indicating an event, or multiple events, can be applied via the ICPn pin or
alternatively, via the analog-comparator unit. The time-stamps can then be used to calculate frequency, duty-cycle, and
other features of the signal applied. Alternatively the time-stamps can be used for creating a log of the events.
The input capture unit is illustrated by the block diagram shown in Figure 16-3 on page 97. The elements of the block
diagram that are not directly a part of the input capture unit are gray shaded. The small “n” in register and bit names
indicates the Timer/Counter number.
Figure 16-3. Input Capture Unit Block Diagram
DATA BUS (8-bit)
TEMP (8-bit)
ICRnH (8-bit)
ICRnL (8-bit)
TCNTnH (8-bit)
TCNTnL (8-bit)
ICRn (16-bit Register)
TCNTn (16-bit Counter)
WRITE
ACO*
ACIC*
ICNC
ICES
+
-
Analog
Comparator
Noise
Canceler
Edge
Detector
ICFn (Int. Req.)
ICPn
When a change of the logic level (an event) occurs on the input capture pin (ICPn), alternatively on the analog comparator
output (ACO), and this change confirms to the setting of the edge detector, a capture will be triggered. When a capture is
triggered, the 16-bit value of the counter (TCNTn) is written to the input capture register (ICRn). The input capture flag (ICFn)
is set at the same system clock as the TCNTn value is copied into ICRn register. If enabled (ICIEn = 1), the input capture flag
generates an input capture interrupt. The ICFn flag is automatically cleared when the interrupt is executed. Alternatively the
ICFn flag can be cleared by software by writing a logical one to its I/O bit location.
Reading the 16-bit value in the input capture register (ICRn) is done by first reading the low byte (ICRnL) and then the high
byte (ICRnH). When the low byte is read the high byte is copied into the high byte temporary register (TEMP). When the
CPU reads the ICRnH I/O location it will access the TEMP register.
The ICRn register can only be written when using a waveform generation mode that utilizes the ICRn register for defining the
counter’s TOP value. In these cases the waveform Generation mode (WGMn3:0) bits must be set before the TOP value can
be written to the ICRn Register. When writing the ICRn register the high byte must be written to the ICRnH I/O location
before the low byte is written to ICRnL.
For more information on how to access the 16-bit registers refer to Section 16.3 “Accessing 16-bit Registers” on page 92.
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16.6.1 Input Capture Trigger Source
The main trigger source for the input capture unit is the input capture pin (ICPn). Timer/Counter1 can alternatively use the
analog comparator output as trigger source for the input capture unit. The analog comparator is selected as trigger source by
setting the analog comparator input capture (ACIC) bit in the analog comparator control and status register (ACSR). Be
aware that changing trigger source can trigger a capture. The input capture flag must therefore be cleared after the change.
Both the input capture pin (ICPn) and the analog comparator output (ACO) inputs are sampled using the same technique as
for the Tn pin (Figure 16-1 on page 91). The edge detector is also identical. However, when the noise canceler is enabled,
additional logic is inserted before the edge detector, which increases the delay by four system clock cycles. Note that the
input of the noise canceler and edge detector is always enabled unless the Timer/Counter is set in a waveform generation
mode that uses ICRn to define TOP.
An input capture can be triggered by software by controlling the port of the ICPn pin.
16.6.2 Noise Canceler
The noise canceler improves noise immunity by using a simple digital filtering scheme. The noise canceler input is monitored
over four samples, and all four must be equal for changing the output that in turn is used by the edge detector.
The noise canceler is enabled by setting the input capture noise canceler (ICNCn) bit in Timer/Counter control register B
(TCCRnB). When enabled the noise canceler introduces additional four system clock cycles of delay from a change applied
to the input, to the update of the ICRn register. The noise canceler uses the system clock and is therefore not affected by the
prescaler.
16.6.3 Using the Input Capture Unit
The main challenge when using the input capture unit is to assign enough processor capacity for handling the incoming
events. The time between two events is critical. If the processor has not read the captured value in the ICRn register before
the next event occurs, the ICRn will be overwritten with a new value. In this case the result of the capture will be incorrect.
When using the input capture interrupt, the ICRn register should be read as early in the interrupt handler routine as possible.
Even though the input capture interrupt has relatively high priority, the maximum interrupt response time is dependent on the
maximum number of clock cycles it takes to handle any of the other interrupt requests.
Using the input capture unit in any mode of operation when the TOP value (resolution) is actively changed during operation,
is not recommended.
Measurement of an external signal’s duty cycle requires that the trigger edge is changed after each capture. Changing the
edge sensing must be done as early as possible after the ICRn register has been read. After a change of the edge, the input
capture flag (ICFn) must be cleared by software (writing a logical one to the I/O bit location). For measuring frequency only,
the clearing of the ICFn flag is not required (if an interrupt handler is used).
16.7 Output Compare Units
The 16-bit comparator continuously compares TCNTn with the output compare register (OCRnx). If TCNT equals OCRnx
the comparator signals a match. A match will set the output compare flag (OCFnx) at the next timer clock cycle. If enabled
(OCIEnx = 1), the output compare flag generates an output compare interrupt. The OCFnx flag is automatically cleared
when the interrupt is executed. Alternatively the OCFnx flag can be cleared by software by writing a logical one to its I/O bit
location. The waveform generator uses the match signal to generate an output according to operating mode set by the
waveform generation mode (WGMn3:0) bits and compare output mode (COMnx1:0) bits. The TOP and BOTTOM signals
are used by the waveform generator for handling the special cases of the extreme values in some modes of operation
(Section 16.9 “Modes of Operation” on page 101).
A special feature of output compare unit A allows it to define the Timer/Counter TOP value (i.e., counter resolution). In
addition to the counter resolution, the TOP value defines the period time for waveforms generated by the waveform
generator.
Figure 16-4 on page 99 shows a block diagram of the output compare unit. The small “n” in the register and bit names
indicates the device number (n = n for Timer/Counter n), and the “x” indicates output compare unit (A/B/C). The elements of
the block diagram that are not directly a part of the output compare unit are gray shaded.
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Figure 16-4. Output Compare Unit, Block Diagram
DATA BUS (8-bit)
TEMP (8-bit)
OCRnxH Buf. (8-bit)
OCRnxL Buf. (8-bit)
TCNTnH (8-bit)
TCNTnL (8-bit)
OCRnx Buffer (16-bit Register)
TCNTn (16-bit Counter)
OCRnxH (8-bit)
OCRnxL (8-bit)
OCRnx (16-bit Register)
(16-bitComparator)
=
OCFnx (Int. Req.)
TOP
Waveform Generator
OCnx
BOTTOM
WGMn3:0
COMnx1:0
The OCRnx register is double buffered when using any of the twelve pulse width modulation (PWM) modes. For the normal
and clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes
the update of the OCRnx compare register to either TOP or BOTTOM of the counting sequence. The synchronization
prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCRnx register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has
access to the OCRnx buffer register, and if double buffering is disabled the CPU will access the OCRnx directly. The content
of the OCR1x (buffer or compare) register is only changed by a write operation (the Timer/Counter does not update this
register automatically as the TCNT1 and ICR1 register). Therefore OCR1x is not read via the high byte temporary register
(TEMP). However, it is a good practice to read the low byte first as when accessing other 16-bit registers. Writing the OCRnx
registers must be done via the TEMP register since the compare of all 16 bits is done continuously. The high byte (OCRnxH)
has to be written first. When the high byte I/O location is written by the CPU, the TEMP register will be updated by the value
written. Then when the low byte (OCRnxL) is written to the lower eight bits, the high byte will be copied into the upper 8-bits
of either the OCRnx buffer or OCRnx compare register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to Section 16.3 “Accessing 16-bit Registers” on page 92.
16.7.1 Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the force
output compare (FOCnx) bit. Forcing compare match will not set the OCFnx flag or reload/clear the timer, but the OCnx pin
will be updated as if a real compare match had occurred (the COMn1:0 bits settings define whether the OCnx pin is set,
cleared or toggled).
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16.7.2 Compare Match Blocking by TCNTn Write
All CPU writes to the TCNTn register will block any compare match that occurs in the next timer clock cycle, even when the
timer is stopped. This feature allows OCRnx to be initialized to the same value as TCNTn without triggering an interrupt
when the Timer/Counter clock is enabled.
16.7.3 Using the Output Compare Unit
Since writing TCNTn in any mode of operation will block all compare matches for one timer clock cycle, there are risks
involved when changing TCNTn when using any of the output compare channels, independent of whether the Timer/Counter
is running or not. If the value written to TCNTn equals the OCRnx value, the compare match will be missed, resulting in
incorrect waveform generation. Do not write the TCNTn equal to TOP in PWM modes with variable TOP values. The
compare match for the TOP will be ignored and the counter will continue to 0xFFFF. Similarly, do not write the TCNTn value
equal to BOTTOM when the counter is downcounting.
The setup of the OCnx should be performed before setting the data direction register for the port pin to output. The easiest
way of setting the OCnx value is to use the force output compare (FOCnx) strobe bits in normal mode. The OCnx register
keeps its value even when changing between waveform generation modes.
Be aware that the COMnx1:0 bits are not double buffered together with the compare value. Changing the COMnx1:0 bits will
take effect immediately.
16.8 Compare Match Output Unit
The compare output mode (COMnx1:0) bits have two functions. The waveform generator uses the COMnx1:0 bits for
defining the output oompare (OCnx) state at the next compare match. Secondly the COMnx1:0 bits control the OCnx pin
output source. Figure 16-5 shows a simplified schematic of the logic affected by the COMnx1:0 bit setting. The I/O registers,
I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O port control registers (DDR and PORT)
that are affected by the COMnx1:0 bits are shown. When referring to the OCnx state, the reference is for the internal OCnx
register, not the OCnx pin. If a system reset occur, the OCnx register is reset to “0”.
Figure 16-5. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCnx
Waveform
Generator
D
D
Q
Q
1
0
OCnx
Pin
OCnx
PORT
D
Q
DDR
clkI/O
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The general I/O port function is overridden by the output compare (OCnx) from the waveform generator if either of the
COMnx1:0 bits are set. However, the OCnx pin direction (input or output) is still controlled by the data direction register
(DDR) for the port pin. The data direction register bit for the OCnx pin (DDR_OCnx) must be set as output before the OCnx
value is visible on the pin. The port override function is generally independent of the Waveform Generation mode, but there
are some exceptions. Refer to Table 16-2 on page 109, Table 16-3 on page 110 and Table 16-4 on page 110 for details.
The design of the output compare pin logic allows initialization of the OCnx state before the output is enabled. Note that
some COMnx1:0 bit settings are reserved for certain modes of operation. Section 16.11 “Register Description” on page 109.
The COMnx1:0 bits have no effect on the input capture unit.
16.8.1 Compare Output Mode and Waveform Generation
The waveform generator uses the COMnx1:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the
COMnx1:0 = 0 tells the waveform generator that no action on the OCnx register is to be performed on the next compare
match. For compare output actions in the non-PWM modes refer to Table 16-2 on page 109. For fast PWM mode refer to
Table 16-3 on page 110, and for phase correct and phase and frequency correct PWM refer to Table 16-4 on page 110.
A change of the COMnx1:0 bits state will have effect at the first compare match after the bits are written. For non-PWM
modes, the action can be forced to have immediate effect by using the FOCnx strobe bits.
16.9 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the output compare pins, is defined by the combination of
the waveform generation mode (WGMn3:0) and compare output mode (COMnx1:0) bits. The compare output mode bits do
not affect the counting sequence, while the waveform generation mode bits do. The COMnx1:0 bits control whether the
PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COMnx1:0 bits
control whether the output should be set, cleared or toggle at a compare match
(Section 16.8 “Compare Match Output Unit” on page 100).
For detailed timing information refer to Section 16.10 “Timer/Counter Timing Diagrams” on page 107.
16.9.1 Normal Mode
The simplest mode of operation is the normal mode (WGMn3:0 = 0). In this mode the counting direction is always up
(incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 16-bit value
(MAX = 0xFFFF) and then restarts from the BOTTOM (0x0000). In normal operation the Timer/Counter overflow flag (TOVn)
will be set in the same timer clock cycle as the TCNTn becomes zero. The TOVn flag in this case behaves like a 17th bit,
except that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOVn
flag, the timer resolution can be increased by software. There are no special cases to consider in the Normal mode, a new
counter value can be written anytime.
The input capture unit is easy to use in normal mode. However, observe that the maximum interval between the external
events must not exceed the resolution of the counter. If the interval between events are too long, the timer overflow interrupt
or the prescaler must be used to extend the resolution for the capture unit.
The output compare units can be used to generate interrupts at some given time. Using the output compare to generate
waveforms in normal mode is not recommended, since this will occupy too much of the CPU time.
16.9.2 Clear Timer on Compare Match (CTC) Mode
In clear timer on compare or CTC mode (WGMn3:0 = 4 or 12), the OCRnA or ICRn register are used to manipulate the
counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNTn) matches either the OCRnA
(WGMn3:0 = 4) or the ICRn (WGMn3:0 = 12). The OCRnA or ICRn define the top value for the counter, hence also its
resolution. This mode allows greater control of the compare match output frequency. It also simplifies the operation of
counting external events.
The timing diagram for the CTC mode is shown in Figure 16-6 on page 102. The counter value (TCNTn) increases until a
compare match occurs with either OCRnA or ICRn, and then counter (TCNTn) is cleared.
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Figure 16-6. CTC Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnA
(COMnA1:0 = 1)
(Toggle)
1
2
3
4
Period
An interrupt can be generated at each time the counter value reaches the TOP value by either using the OCFnA or ICFn flag
according to the register used to define the TOP value. If the interrupt is enabled, the interrupt handler routine can be used
for updating the TOP value. However, changing the TOP to a value close to BOTTOM when the counter is running with none
or a low prescaler value must be done with care since the CTC mode does not have the double buffering feature. If the new
value written to OCRnA or ICRn is lower than the current value of TCNTn, the counter will miss the compare match. The
counter will then have to count to its maximum value (0xFFFF) and wrap around starting at 0x0000 before the compare
match can occur. In many cases this feature is not desirable. An alternative will then be to use the fast PWM mode using
OCRnA for defining TOP (WGMn3:0 = 15) since the OCRnA then will be double buffered.
For generating a waveform output in CTC mode, the OCnA output can be set to toggle its logical level on each compare
match by setting the compare output mode bits to toggle mode (COMnA1:0 = 1). The OCnA value will not be visible on the
port pin unless the data direction for the pin is set to output (DDR_OCnA = 1). The waveform generated will have a
maximum frequency of fOCnA = fclk_I/O/2 when OCRnA is set to zero (0x0000). The waveform frequency is defined by the
following equation:
f
clk_I/O
-------------------------------------------------
f
=
OCnA
2 N (1 + OCRnA)
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the normal mode of operation, the TOVn flag is set in the same timer clock cycle that the counter counts from MAX to
0x0000.
16.9.3 Fast PWM Mode
The fast pulse width modulation or fast PWM mode (WGMn3:0 = 5, 6, 7, 14, or 15) provides a high frequency PWM
waveform generation option. The fast PWM differs from the other PWM options by its single-slope operation. The counter
counts from BOTTOM to TOP then restarts from BOTTOM. In non-inverting compare output mode, the output compare
(OCnx) is cleared on the compare match between TCNTn and OCRnx, and set at BOTTOM. In inverting compare output
mode output is set on compare match and cleared at BOTTOM. Due to the single-slope operation, the operating frequency
of the fast PWM mode can be twice as high as the phase correct and phase and frequency correct PWM modes that use
dual-slope operation. This high frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC
applications. High frequency allows physically small sized external components (coils, capacitors), hence reduces total
system cost.
The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICRn or OCRnA. The minimum
resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and the maximum resolution is 16-bit (ICRn or OCRnA set to
MAX). The PWM resolution in bits can be calculated by using the following equation:
log(TOP + 1)
---------------------------------
=
R
FPWM
log(2)
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In fast PWM mode the counter is incremented until the counter value matches either one of the fixed values 0x00FF,
0x01FF, or 0x03FF (WGMn3:0 = 5, 6, or 7), the value in ICRn (WGMn3:0 = 14), or the value in OCRnA (WGMn3:0 = 15).
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast PWM mode is shown in
Figure 16-7. The figure shows fast PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn value is in the
timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNTn slopes represent compare matches between OCRnx
and TCNTn. The OCnx interrupt flag will be set when a compare match occurs.
Figure 16-7. Fast PWM Mode, Timing Diagram
OCRnx/ TOP Update and
TOVn Interrupt Flag Set and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCnx
1
2
3
4
5
6
7
8
Period
The Timer/Counter overflow flag (TOVn) is set each time the counter reaches TOP. In addition the OCnA or ICFn flag is set
at the same timer clock cycle as TOVn is set when either OCRnA or ICRn is used for defining the TOP value. If one of the
interrupts are enabled, the interrupt handler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the
compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between
the TCNTn and the OCRnx. Note that when using fixed TOP values the unused bits are masked to zero when any of the
OCRnx registers are written.
The procedure for updating ICRn differs from updating OCRnA when used for defining the TOP value. The ICRn register is
not double buffered. This means that if ICRn is changed to a low value when the counter is running with none or a low
prescaler value, there is a risk that the new ICRn value written is lower than the current value of TCNTn. The result will then
be that the counter will miss the compare match at the TOP value. The counter will then have to count to the MAX value
(0xFFFF) and wrap around starting at 0x0000 before the compare match can occur. The OCRnA register however, is double
buffered. This feature allows the OCRnA I/O location to be written anytime. When the OCRnA I/O location is written the
value written will be put into the OCRnA buffer register. The OCRnA compare register will then be updated with the value in
the buffer register at the next timer clock cycle the TCNTn matches TOP. The update is done at the same timer clock cycle
as the TCNTn is cleared and the TOVn flag is set.
Using the ICRn register for defining TOP works well when using fixed TOP values. By using ICRn, the OCRnA register is
free to be used for generating a PWM output on OCnA. However, if the base PWM frequency is actively changed (by
changing the TOP value), using the OCRnA as TOP is clearly a better choice due to its double buffer feature.
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In fast PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins. Setting the COMnx1:0 bits to
two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COMnx1:0 to three (see
Table on page 110). The actual OCnx value will only be visible on the port pin if the data direction for the port pin is set as
output (DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx register at the compare match
between OCRnx and TCNTn, and clearing (or setting) the OCnx register at the timer clock cycle the counter is cleared
(changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f
clk_I/O
----------------------------------
f
=
OCnxPWM
N (1 + TOP)
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCRnx register represents special cases when generating a PWM waveform output in the fast
PWM mode. If the OCRnx is set equal to BOTTOM (0x0000) the output will be a narrow spike for each TOP+1 timer clock
cycle. Setting the OCRnx equal to TOP will result in a constant high or low output (depending on the polarity of the output set
by the COMnx1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OCnA to toggle its logical
level on each compare match (COMnA1:0 = 1). This applies only if OCR1A is used to define the TOP value
(WGM13:0 = 15). The waveform generated will have a maximum frequency of fOCnA = fclk_I/O/2 when OCRnA is set to zero
(0x0000). This feature is similar to the OCnA toggle in CTC mode, except the double buffer feature of the output compare
unit is enabled in the fast PWM mode.
16.9.4 Phase Correct PWM Mode
The phase correct pulse width modulation or phase correct PWM mode (WGMn3:0 = 1, 2, 3, 10, or 11) provides a high
resolution phase correct PWM waveform generation option. The phase correct PWM mode is, like the phase and frequency
correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and
then from TOP to BOTTOM. In non-inverting compare output mode, the output compare (OCnx) is cleared on the compare
match between TCNTn and OCRnx while upcounting, and set on the compare match while downcounting. In inverting output
compare mode, the operation is inverted. The dual-slope operation has lower maximum operation frequency than single
slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor
control applications.
The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or defined by either ICRn or OCRnA.
The minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and the maximum resolution is 16-bit (ICRn or
OCRnA set to MAX). The PWM resolution in bits can be calculated by using the following equation:
log(TOP + 1)
---------------------------------
=
R
PCPWM
log(2)
In phase correct PWM mode the counter is incremented until the counter value matches either one of the fixed values
0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 1, 2, or 3), the value in ICRn (WGMn3:0 = 10), or the value in OCRnA
(WGMn3:0 = 11). The counter has then reached the TOP and changes the count direction. The TCNTn value will be equal to
TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 16-8 on page 105.
The figure shows phase correct PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn value is in the timing
diagram shown as a histogram for illustrating the dual-slope operation. The diagram includes non-inverted and inverted
PWM outputs. The small horizontal line marks on the TCNTn slopes represent compare matches between OCRnx and
TCNTn. The OCnx interrupt flag will be set when a compare match occurs.
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Figure 16-8. Phase Correct PWM Mode, Timing Diagram
OCRnx/ TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
1
2
3
4
Period
The Timer/Counter overflow flag (TOVn) is set each time the counter reaches BOTTOM. When either OCRnA or ICRn is
used for defining the TOP value, the OCnA or ICFn flag is set accordingly at the same timer clock cycle as the OCRnx
registers are updated with the double buffer value (at TOP). The interrupt flags can be used to generate an interrupt each
time the counter reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the
compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between
the TCNTn and the OCRnx. Note that when using fixed TOP values, the unused bits are masked to zero when any of the
OCRnx registers are written. As the third period shown in Figure 16-8 illustrates, changing the TOP actively while the
Timer/Counter is running in the phase correct mode can result in an unsymmetrical output. The reason for this can be found
in the time of update of the OCRnx register. Since the OCRnx update occurs at TOP, the PWM period starts and ends at
TOP. This implies that the length of the falling slope is determined by the previous TOP value, while the length of the rising
slope is determined by the new TOP value. When these two values differ the two slopes of the period will differ in length. The
difference in length gives the unsymmetrical result on the output.
It is recommended to use the phase and frequency correct mode instead of the phase correct mode when changing the TOP
value while the Timer/Counter is running. When using a static TOP value there are practically no differences between the
two modes of operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins. Setting the
COMnx1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the
COMnx1:0 to three (See Table on page 110). The actual OCnx value will only be visible on the port pin if the data direction
for the port pin is set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx register at
the compare match between OCRnx and TCNTn when the counter increments, and clearing (or setting) the OCnx register at
compare match between OCRnx and TCNTn when the counter decrements. The PWM frequency for the output when using
phase correct PWM can be calculated by the following equation:
f
clk_I/O
---------------------------
f
=
OCnxPCPWM
2 N TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCRnx register represent special cases when generating a PWM waveform output in the phase
correct PWM mode. If the OCRnx is set equal to BOTTOM the output will be continuously low and if set equal to TOP the
output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic
values. If OCR1A is used to define the TOP value (WGM13:0 = 11) and COM1A1:0 = 1, the OC1A output will toggle with a
50% duty cycle.
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16.9.5 Phase and Frequency Correct PWM Mode
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM mode (WGMn3:0 = 8 or 9)
provides a high resolution phase and frequency correct PWM waveform generation option. The phase and frequency correct
PWM mode is, like the phase correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from
BOTTOM (0x0000) to TOP and then from TOP to BOTTOM. In non-inverting compare output mode, the output compare
(OCnx) is cleared on the compare match between TCNTn and OCRnx while upcounting, and set on the compare match
while downcounting. In inverting compare output mode, the operation is inverted. The dual-slope operation gives a lower
maximum operation frequency compared to the single-slope operation. However, due to the symmetric feature of the
dual-slope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct PWM mode is the time the OCRnx
register is updated by the OCRnx buffer register, (see Figure 16-8 on page 105 and Figure 16-9).
The PWM resolution for the phase and frequency correct PWM mode can be defined by either ICRn or OCRnA. The
minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and the maximum resolution is 16-bit (ICRn or OCRnA
set to MAX). The PWM resolution in bits can be calculated using the following equation:
log(TOP + 1)
---------------------------------
=
R
PFCPWM
log(2)
In phase and frequency correct PWM mode the counter is incremented until the counter value matches either the value in
ICRn (WGMn3:0 = 8), or the value in OCRnA (WGMn3:0 = 9). The counter has then reached the TOP and changes the
count direction. The TCNTn value will be equal to TOP for one timer clock cycle. The timing diagram for the phase correct
and frequency correct PWM mode is shown on Figure 16-9. The figure shows phase and frequency correct PWM mode
when OCRnA or ICRn is used to define TOP. The TCNTn value is in the timing diagram shown as a histogram for illustrating
the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on
the TCNTn slopes represent compare matches between OCRnx and TCNTn. The OCnx interrupt flag will be set when a
compare match occurs.
Figure 16-9. Phase and Frequency Correct PWM Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
OCRnx/ TOP Update and
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
(COMnx1:0 = 2)
OCnx
OCnx
(COMnx1:0 = 3)
1
2
3
4
Period
The Timer/Counter overflow flag (TOVn) is set at the same timer clock cycle as the OCRnx registers are updated with the
double buffer value (at BOTTOM). When either OCRnA or ICRn is used for defining the TOP value, the OCnA or ICFn flag
set when TCNTn has reached TOP. The interrupt flags can then be used to generate an interrupt each time the counter
reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the
compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between
the TCNTn and the OCRnx.
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As Figure 16-9 on page 106 shows the output generated is, in contrast to the phase correct mode, symmetrical in all periods.
Since the OCRnx registers are updated at BOTTOM, the length of the rising and the falling slopes will always be equal. This
gives symmetrical output pulses and is therefore frequency correct.
Using the ICRn register for defining TOP works well when using fixed TOP values. By using ICRn, the OCRnA register is
free to be used for generating a PWM output on OCnA. However, if the base PWM frequency is actively changed by
changing the TOP value, using the OCRnA as TOP is clearly a better choice due to its double buffer feature.
In phase and frequency correct PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins.
Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting
the COMnx1:0 to three (See Table on page 110). The actual OCnx value will only be visible on the port pin if the data
direction for the port pin is set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx
register at the compare match between OCRnx and TCNTn when the counter increments, and clearing (or setting) the OCnx
register at compare match between OCRnx and TCNTn when the counter decrements. The PWM frequency for the output
when using phase and frequency correct PWM can be calculated by the following equation:
f
clk_I/O
---------------------------
f
=
OCnxPFCPWM
2 N TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCRnx register represents special cases when generating a PWM waveform output in the phase
correct PWM mode. If the OCRnx is set equal to BOTTOM the output will be continuously low and if set equal to TOP the
output will be set to high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If
OCR1A is used to define the TOP value (WGM13:0 = 9) and COM1A1:0 = 1, the OC1A output will toggle with a 50% duty
cycle.
16.10 Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkTn) is therefore shown as a clock enable signal in the
following figures. The figures include information on when interrupt flags are set, and when the OCRnx register is updated
with the OCRnx buffer value (only for modes utilizing double buffering). Figure 16-10 shows a timing diagram for the setting
of OCFnx.
Figure 16-10. Timer/Counter Timing Diagram, Setting of OCFnx, no Prescaling
clkI/O
clkTn
(clkI/O/1)
TCNTn
OCRnx
OCFnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
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Figure 16-11 shows the same timing data, but with the prescaler enabled.
Figure 16-11. Timer/Counter Timing Diagram, Setting of OCFnx, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx
OCFnx
OCRnx Value
Figure 16-12 shows the count sequence close to TOP in various modes. When using phase and frequency correct PWM
mode the OCRnx register is updated at BOTTOM. The timing diagrams will be the same, but TOP should be replaced by
BOTTOM, TOP-1 by BOTTOM+1 and so on. The same renaming applies for modes that set the TOVn flag at BOTTOM.
Figure 16-12. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O/1)
TCNTn
TOP - 1
TOP - 1
TOP
TOP
BOTTOM
TOP -1
BOTTOM + 1
TOP -2
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOVn (FPWM)
and ICFn
(if used as TOP)
OCRnx
(Update at TOP)
Old OCRnx Value
New OCRnx Value
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Figure 16-13 shows the same timing data, but with the prescaler enabled.
Figure 16-13. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
TOP - 1
TOP - 1
TOP
TOP
BOTTOM
TOP - 1
BOTTOM + 1
TOP - 2
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOVn (FPWM)
and ICFn
(if used as TOP)
OCRnx
(Update at TOP)
Old OCRnx Value
New OCRnx Value
16.11 Register Description
16.11.1 TCCRnA – Timer/Counter n Control Register A
Bit
7
6
5
4
3
2
–
1
0
(0x80)
COMnA1 COMnA0 COMnB1 COMnB0
–
WGMn1 WGMn0 TCCRnA
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R
0
R
0
R/W
0
R/W
0
• Bit 7:6 – COMnA1:0: Compare Output Mode for Channel A
• Bit 5:4 – COMnB1:0: Compare Output Mode for Channel B
The COMnA1:0 and COMnB1:0 control the output compare pins (OCnA and OCnB respectively) behavior. If one or both of
the COMnA1:0 bits are written to one, the OCnA output overrides the normal port functionality of the I/O pin it is connected
to. If one or both of the COMnB1:0 bit are written to one, the OCnB output overrides the normal port functionality of
the I/O pin it is connected to. However, note that the data direction register (DDR) bit corresponding to the OCnA or OCnB
pin must be set in order to enable the output driver.
When the OCnA or OCnB is connected to the pin, the function of the COMnx1:0 bits is dependent of the WGMn3:0 bits
setting. Table 16-2 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to a normal or a CTC mode
(non-PWM).
Table 16-2. Compare Output Mode, non-PWM
COMnA1/COMnB1
COMnA0/COMnB0
Description
0
0
1
1
0
1
0
1
Normal port operation, OCnA/OCnB disconnected.
Toggle OCnA/OCnB on compare match.
Clear OCnA/OCnB on compare match (set output to low level)
Set OCnA/OCnB on compare match (set output to high level)
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Table 16-3 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the fast PWM mode.
Table 16-3. Compare Output Mode, Fast PWM(1)
COMnA1/COMnB1
COMnA0/COMnB0
Description
0
0
Normal port operation, OCnA/OCnB disconnected.
WGMn3:0 = 14 or 15: Toggle OC1A on compare match, OC1B
disconnected (normal port operation). For all other WGM1
settings, normal port operation, OC1A/OC1B disconnected.
0
1
Clear OCnA/OCnB on compare match, set OCnA/OCnB at
BOTTOM (non-inverting mode)
1
1
0
1
Set OCnA/OCnB on compare match, clear OCnA/OCnB at
BOTTOM (inverting mode)
Note:
1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set. In this case the
compare match is ignored, but the set or clear is done at BOTTOM.
See Section 16.9.3 “Fast PWM Mode” on page 102 for more details.
Table 16-4 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the phase correct or the phase and
frequency correct, PWM mode.
Table 16-4. Compare Output Mode, Phase Correct and Phase and Frequency Correct PWM(1)
COMnA1/COMnB1
COMnA0/COMnB0
Description
0
0
Normal port operation, OCnA/OCnB disconnected.
WGMn3:0 = 9 or 11: Toggle OCnA on compare match, OCnB
disconnected (normal port operation). For all other WGM1
settings, normal port operation, OC1A/OC1B disconnected.
0
1
Clear OCnA/OCnB on compare match when up-counting. Set
OCnA/OCnB on compare match when downcounting.
1
1
0
1
Set OCnA/OCnB on compare match when up-counting. Clear
OCnA/OCnB on compare match when downcounting.
Note:
1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set.
See Section 16.9.4 “Phase Correct PWM Mode” on page 104 for more details.
• Bit 1:0 – WGMn1:0: Waveform Generation Mode
Combined with the WGMn3:2 bits found in the TCCRnB register, these bits control the counting sequence of the counter, the
source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 16-5. Modes of
operation supported by the Timer/Counter unit are: Normal mode (counter), clear timer on compare match (CTC) mode, and
three types of pulse width modulation (PWM) modes. See (Section 16.9 “Modes of Operation” on page 101).
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Table 16-5. Waveform Generation Mode Bit Description(1)
WGMn2 WGMn1 WGMn0 Timer/Counter Mode of
(CTCn) (PWMn1) (PWMn0) Operation
Normal
Update of TOVn Flag
OCRnx at Set on
Mode WGMn3
TOP
0
1
2
3
4
5
6
7
0
0
0
0
0
0
0
0
0
0
0
0xFFFF
0x00FF
0x01FF
Immediate MAX
0
0
1
PWM, phase correct, 8-bit
PWM, phase correct, 9-bit
TOP
TOP
TOP
BOTTOM
BOTTOM
BOTTOM
0
0
1
1
1
1
1
1
0
0
1
1
0
1
0
1
0
1
PWM, phase correct, 10-bit 0x03FF
CTC
OCRnA
0x00FF
0x01FF
0x03FF
Immediate MAX
Fast PWM, 8-bit
Fast PWM, 9-bit
Fast PWM, 10-bit
BOTTOM
BOTTOM
BOTTOM
TOP
TOP
TOP
PWM, phase and frequency
correct
8
9
1
1
0
0
0
0
0
1
ICRn
BOTTOM
BOTTOM
BOTTOM
BOTTOM
PWM, phase and frequency
correct
OCRnA
10
11
12
13
14
1
1
1
1
1
1
0
0
1
1
1
1
1
1
0
0
1
1
0
1
0
1
0
1
PWM, phase correct
PWM, phase correct
CTC
ICRn
OCRnA
ICRn
–
TOP
TOP
BOTTOM
BOTTOM
Immediate MAX
(Reserved)
–
–
Fast PWM
ICRn
OCRnA
BOTTOM
BOTTOM
TOP
TOP
15
Fast PWM
Note:
1. The CTCn and PWMn1:0 bit definition names are obsolete. Use the WGMn2:0 definitions. However,
the functionality and location of these bits are compatible with previous versions of the timer.
16.11.2 TCCRnB – Timer/Counter n Control Register B
Bit
7
ICNCn
R/W
0
6
ICESn
R/W
0
5
–
4
3
2
CSn2
R/W
0
1
CSn1
R/W
0
0
CSn0
R/W
0
(0x81)
WGMn3 WGMn2
TCCRnB
Read/Write
Initial Value
R
0
R/W
0
R/W
0
• Bit 7 – ICNCn: Input Capture Noise Canceler
Setting this bit (to one) activates the input capture noise canceler. When the noise canceler is activated, the input from the
input capture pin (ICPn) is filtered. The filter function requires four successive equal valued samples of the ICPn pin for
changing its output. The input capture is therefore delayed by four oscillator cycles when the noise canceler is enabled.
• Bit 6 – ICESn: Input Capture Edge Select
This bit selects which edge on the input capture pin (ICPn) that is used to trigger a capture event. When the ICESn bit is
written to zero, a falling (negative) edge is used as trigger, and when the ICESn bit is written to one, a rising (positive) edge
will trigger the capture.
When a capture is triggered according to the ICESn setting, the counter value is copied into the input capture register
(ICRn). The event will also set the input capture flag (ICFn), and this can be used to cause an input capture interrupt, if this
interrupt is enabled.
When the ICRn is used as TOP value (see description of the WGMn3:0 bits located in the TCCRnA and the TCCRnB
register), the ICPn is disconnected and consequently the input capture function is disabled.
• Bit 5 – Reserved
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be written to zero when
TCCRnB is written.
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• Bit 4:3 – WGMn3:2: Waveform Generation Mode
See description of Section 16.11.1 “TCCRnA – Timer/Counter n Control Register A” on page 109.
• Bit 2:0 – CSn2:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter, see Figure 16-10 on page 107 and
Figure 16-11 on page 108.
Table 16-6. Clock Select Bit Description
CSn2
CSn1
CSn0
Description
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
No clock source (Timer/Counter stopped).
clkI/O/1 (no prescaling)
clkI/O/8 (from prescaler)
clkI/O/64 (from prescaler)
clkI/O/256 (from prescaler)
clkI/O/1024 (from prescaler)
External clock source on Tn pin. Clock on falling edge.
External clock source on Tn pin. Clock on rising edge.
If external pin modes are used for the Timer/Countern, transitions on the Tn pin will clock the counter even if the pin is
configured as an output. This feature allows software control of the counting.
16.11.3 TCCRnC – Timer/Counter n Control Register C
Bit
7
6
5
–
4
–
3
–
2
–
1
–
0
–
(0x82)
FOCnA FOCnB
TCCRnC
Read/Write
Initial Value
R/W
0
R/W
0
R
0
R
0
R
0
R
0
R
0
R
0
• Bit 7 – FOCnA: Force Output Compare for Channel A
• Bit 6 – FOCnB: Force Output Compare for Channel B
The FOCnA/FOCnB bits are only active when the WGMn3:0 bits specifies a non-PWM mode. However, for ensuring
compatibility with future devices, these bits must be set to zero when TCCRnA is written when operating in a PWM mode.
When writing a logical one to the FOCnA/FOCnB bit, an immediate compare match is forced on the waveform generation
unit. The OCnA/OCnB output is changed according to its COMnx1:0 bits setting. Note that the FOCnA/FOCnB bits are
implemented as strobes. Therefore it is the value present in the COMnx1:0 bits that determine the effect of the forced
compare.
A FOCnA/FOCnB strobe will not generate any interrupt nor will it clear the timer in clear timer on compare match (CTC)
mode using OCRnA as TOP.
The FOCnA/FOCnB bits are always read as zero.
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16.11.4 TCNT1H and TCNT1L –Timer/Counter1
Bit
7
6
5
4
3
2
1
0
(0x85)
TCNT1[15:8]
TCNT1[7:0]
TCNT1H
TCNT1L
(0x84)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
R/W
R/W
0
R/W
0
R/W
0
0
0
The two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give direct access, both for read and for
write operations, to the Timer/Counter unit 16-bit counter. To ensure that both the high and low bytes are read and written
simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary high byte register
(TEMP). This temporary register is shared by all the other 16-bit registers.
See Section 16.3 “Accessing 16-bit Registers” on page 92.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a compare match between TCNT1
and one of the OCRnx registers.
Writing to the TCNT1 register blocks (removes) the compare match on the following timer clock for all compare units.
16.11.5 TCNT3H and TCNT3L –Timer/Counter3
Bit
7
6
5
4
3
2
1
0
(0x95)
TCNT3[15:8]
TCNT3[7:0]
TCNT3H
TCNT3L
(0x94)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
R/W
R/W
0
R/W
0
R/W
0
0
0
The two Timer/Counter I/O locations (TCNT3H and TCNT3L, combined TCNT3) give direct access, both for read and for
write operations, to the Timer/Counter unit 16-bit counter. To ensure that both the high and low bytes are read and written
simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary high byte register
(TEMP). This temporary register is shared by all the other 16-bit registers.
See Section 16.3 “Accessing 16-bit Registers” on page 92.
Modifying the counter (TCNT3) while the counter is running introduces a risk of missing a compare match between TCNT3
and one of the OCRnx registers.
Writing to the TCNT3 register blocks (removes) the compare match on the following timer clock for all compare units.
16.11.6 OCR1AH and OCR1AL – Output Compare Register1 A
Bit
7
6
5
4
3
2
1
0
(0x89)
OCR1A[15:8]
OCR1A[7:0]
OCR1AH
OCR1AL
(0x88)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
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16.11.7 OCR1BH and OCR1BL – Output Compare Register1 B
Bit
7
6
5
4
3
2
1
0
(0x8B)
OCR1B[15:8]
OCR1B[7:0]
OCR1BH
OCR1BL
(0x8A)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
The output compare registers contain a 16-bit value that is continuously compared with the counter value (TCNT1). A match
can be used to generate an output compare interrupt, or to generate a waveform output on the OCnx pin.
The output compare registers are 16-bit in size. To ensure that both the high and low bytes are written simultaneously when
the CPU writes to these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This
temporary register is shared by all the other 16-bit registers. See Section 16.3 “Accessing 16-bit Registers” on page 92.
16.11.8 OCR3AH and OCR3AL – Output Compare Register3 A
Bit
7
6
5
4
3
2
1
0
(0x99)
OCR3A[15:8]
OCR3A[7:0]
OCR3AH
OCR3AL
(0x98)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
16.11.9 OCR3BH and OCR3BL – Output Compare Register3 B
Bit
7
6
5
4
3
2
1
0
(0x9B)
OCR3B[15:8]
OCR3B[7:0]
OCR3BH
OCR3BL
(0x9A)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
The output compare registers contain a 16-bit value that is continuously compared with the counter value (TCNT3). A match
can be used to generate an output compare interrupt, or to generate a waveform output on the OCnx pin.
The output compare registers are 16-bit in size. To ensure that both the high and low bytes are written simultaneously when
the CPU writes to these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This
temporary register is shared by all the other 16-bit registers. See Section 16.3 “Accessing 16-bit Registers” on page 92.
16.11.10 ICR1H and ICR1L – Input Capture Register 1
Bit
7
6
5
4
3
2
1
0
(0x87)
ICR1[15:8]
ICR1[7:0]
ICR1H
ICR1L
(0x86)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
R/W
0
R/W
0
R/W
0
R/W
0
0
The input capture is updated with the counter (TCNT1) value each time an event occurs on the ICPn pin (or optionally on the
analog comparator output for Timer/Counter1). The input capture can be used for defining the counter TOP value.
The input capture register is 16-bit in size. To ensure that both the high and low bytes are read simultaneously when the
CPU accesses these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This temporary
register is shared by all the other 16-bit registers. See Section 16.3 “Accessing 16-bit Registers” on page 92.
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16.11.11 ICR3H and ICR3L – Input Capture Register 3
Bit
7
6
5
4
3
2
1
0
(0x97)
ICR3[15:8]
ICR3[7:0]
ICR3H
ICR3L
(0x96)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
R/W
0
R/W
0
R/W
0
R/W
0
0
The input capture is updated with the counter (TCNT3) value each time an event occurs on the ICPn pin (or optionally on the
analog comparator output for Timer/Counter3). The input capture can be used for defining the counter TOP value.
The input capture register is 16-bit in size. To ensure that both the high and low bytes are read simultaneously when the
CPU accesses these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This temporary
register is shared by all the other 16-bit registers. See Section 16.3 “Accessing 16-bit Registers” on page 92.
16.11.12 TIMSK1 – Timer/Counter1 Interrupt Mask Register
Bit
7
–
6
–
5
ICIE1
R/W
0
4
–
3
–
2
1
0
TOIE1
R/W
0
(0x6F)
OCIE1B OCIE1A
TIMSK1
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R/W
0
R/W
0
• Bit 7:6 – Reserved
These bits are unused and will always read as zero.
• Bit 5 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
input capture interrupt is enabled. The corresponding interrupt vector (see Section 12. “Interrupts” on page 49) is executed
when the ICF1 flag, located in TIFR1, is set.
• Bit 4:3 – Reserved
These bits are unused and will always read as zero.
• Bit 2 – OCIE1B: Timer/Counter1, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
output compare B match interrupt is enabled. The corresponding interrupt vector (see Section 12. “Interrupts” on page 49) is
executed when the OCF1B flag, located in TIFR1, is set.
• Bit 1 – OCIE1A: Timer/Counter1, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
output compare A match interrupt is enabled. The corresponding interrupt vector (see Section 12. “Interrupts” on page 49) is
executed when the OCF1A flag, located in TIFR1, is set.
• Bit 0 – TOIE1: Timer/Counter1, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
overflow interrupt is enabled. The corresponding interrupt vector (see Section 11.3 “Watchdog Timer” on page 44) is
executed when the TOV1 flag, located in TIFR1, is set.
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16.11.13 TIMSK3 – Timer/Counter3 Interrupt Mask Register
Bit
7
–
6
–
5
ICIE3
R/W
0
4
–
3
–
2
1
0
TOIE3
R/W
0
(0x71)
OCIE3B OCIE3A
TIMSK3
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R/W
0
R/W
0
• Bit 7:6 – Reserved
These bits are unused and will always read as zero.
• Bit 5 – ICIE3: Timer/Counter3, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
input capture interrupt is enabled. The corresponding interrupt vector (see Section 12. “Interrupts” on page 49) is executed
when the ICF3 flag, located in TIFR3, is set.
• Bit 4:3 – Reserved
These bits are unused and will always read as zero.
• Bit 2 – OCIE3B: Timer/Counter3, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter3
output compare B match interrupt is enabled. The corresponding interrupt vector (see Section 12. “Interrupts” on page 49) is
executed when the OCF3B flag, located in TIFR3, is set.
• Bit 1 – OCIE3A: Timer/Counter3, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter3
output compare A match interrupt is enabled. The corresponding interrupt vector (see Section 12. “Interrupts” on page 49) is
executed when the OCF3A flag, located in TIFR3, is set.
• Bit 0 – TOIE3: Timer/Counter3, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter3
overflow interrupt is enabled. The corresponding interrupt vector (see Section 11.3 “Watchdog Timer” on page 44) is
executed when the TOV3 flag, located in TIFR3, is set.
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16.11.14 TIFR1 – Timer/Counter1 Interrupt Flag Register
Bit
7
–
6
–
5
4
–
3
–
2
OCF1B
R/W
0
1
OCF1A
R/W
0
0
TOV1
R/W
0
0x16 (0x36)
Read/Write
Initial Value
ICF1
R/W
0
TIFR1
R
0
R
0
R
0
R
0
• Bit 7:6 – Reserved
These bits are unused and will always read as zero.
• Bit 5 – ICF1: Timer/Counter1, Input Capture Flag
This flag is set when a capture event occurs on the ICP1 pin. When the input capture register (ICR1) is set by the WGMn3:0
to be used as the TOP value, the ICF1 flag is set when the counter reaches the TOP value.
ICF1 is automatically cleared when the input capture interrupt vector is executed. Alternatively, ICF1 can be cleared by
writing a logic one to its bit location.
• Bit 4:3 – Reserved
These bits are unused and will always read as zero.
• Bit 2 – OCF1B: Timer/Counter1, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the output compare register B (OCR1B).
Note that a forced output compare (FOC1B) strobe will not set the OCF1B flag.
OCF1B is automatically cleared when the output compare match B interrupt vector is executed. Alternatively, OCF1B can be
cleared by writing a logic one to its bit location.
• Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the output compare register A (OCR1A).
Note that a forced output compare (FOC1A) strobe will not set the OCF1A flag.
OCF1A is automatically cleared when the output compare match A interrupt vector is executed. Alternatively, OCF1A can be
cleared by writing a logic one to its bit location.
• Bit 0 – TOV1: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGMn3:0 bits setting. In normal and CTC modes, the TOV1 flag is set when the
timer overflows. Refer to Table 16-5 on page 111 for the TOV1 flag behavior when using another WGMn3:0 bit setting.
TOV1 is automatically cleared when the Timer/Counter1 overflow interrupt vector is executed. Alternatively, TOV1 can be
cleared by writing a logic one to its bit location.
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16.11.15 TIFR3 – Timer/Counter3 Interrupt Flag Register
Bit
7
–
6
–
5
4
–
3
–
2
OCF3B
R/W
0
1
OCF3A
R/W
0
0
TOV3
R/W
0
0x18 (0x38)
Read/Write
Initial Value
ICF3
R/W
0
TIFR3
R
0
R
0
R
0
R
0
• Bit 7:6 – Reserved
These bits are unused and will always read as zero.
• Bit 5 – ICF3: Timer/Counter3, Input Capture Flag
This flag is set when a capture event occurs on the ICP3 pin. When the input capture register (ICR1) is set by the WGMn3:0
to be used as the TOP value, the ICF3 flag is set when the counter reaches the TOP value.
ICF3 is automatically cleared when the input capture interrupt vector is executed. Alternatively, ICF3 can be cleared by
writing a logic one to its bit location.
• Bit 4:3 – Reserved
These bits are unused and will always read as zero.
• Bit 2 – OCF3B: Timer/Counter3, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT3) value matches the output compare register B (OCR3B).
Note that a forced output compare (FOC3B) strobe will not set the OCF3B flag.
OCF3B is automatically cleared when the output compare match B interrupt vector is executed. Alternatively, OCF3B can be
cleared by writing a logic one to its bit location.
• Bit 1 – OCF3A: Timer/Counter3, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT3) value matches the output compare register A (OCR3A).
Note that a forced output compare (FOC3A) strobe will not set the OCF3A flag.
OCF3A is automatically cleared when the output compare match A interrupt vector is executed. Alternatively, OCF3A can be
cleared by writing a logic one to its bit location.
• Bit 0 – TOV3: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGMn3:0 bits setting. In normal and CTC modes, the TOV3 flag is set when the
timer overflows. Refer to Table 16-5 on page 111 for the TOV3 flag behavior when using another WGMn3:0 bit setting.
TOV3 is automatically cleared when the Timer/Counter3 overflow interrupt vector is executed. Alternatively, TOV3 can be
cleared by writing a logic one to its bit location.
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17. 8-bit Timer/Counter2 with PWM and Asynchronous Operation
17.1 Features
●
●
●
●
●
●
●
Single channel counter
Clear timer on compare match (auto reload)
Glitch-free, phase correct pulse width modulator (PWM)
Frequency generator
10-bit clock prescaler
Overflow and compare match interrupt sources (TOV2, OCF2A and OCF2B)
Allows clocking from external 32kHz watch crystal independent of the I/O clock
17.2 Overview
Timer/Counter2 is a general purpose, single channel, 8-bit Timer/Counter module.
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 16-12 on page 108. For the actual placement of I/O
pins, see Section 1. “Pin Configurations” on page 3. CPU accessible I/O registers, including I/O bits and I/O pins, are shown
in bold. The device-specific I/O register and bit locations are listed in the Section 17.11 “Register Description” on page 132.
The power reduction Timer/Counter2 bit, PRTIM2, in Section 10.12.3 “PRR0 – Power Reduction Register 0” on page 39
must be written to zero to enable Timer/Counter2 module.
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Figure 17-1. 8-bit Timer/Counter Block Diagram
Count
Clear
Direction
TOVn (Int. Req.)
Control Logic
clkTn
TOSC1
TOSC2
T/C
Oscillator
Prescaler
TOP
BOTTOM
clkI/O
Timer/Counter
TCNTn
=
=
0
OCnA (Int. Req.)
Waveform
Generation
OCnA
=
OCRnA
Fixed
TOP
Value
OCnB (Int. Req.)
Waveform
Generation
OCnB
=
OCRnB
clkI/O
Synchronized Status flags
Synchronization Unit
clkASY
asynchronous mode
select (ASn)
Status flags
ASSRn
TCCRnA
TCCRnB
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17.2.1 Registers
The Timer/Counter (TCNT2) and output compare register (OCR2A and OCR2B) are 8-bit registers. Interrupt request
(abbreviated to int.req.) signals are all visible in the timer interrupt flag register (TIFR2). All interrupts are individually masked
with the timer interrupt mask register (TIMSK2). TIFR2 and TIMSK2 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or asynchronously clocked from the TOSC1/2 pins, as
detailed later in this section. The asynchronous operation is controlled by the asynchronous status register (ASSR). The
clock select logic block controls which clock source the Timer/Counter uses to increment (or decrement) its value. The
Timer/Counter is inactive when no clock source is selected. The output from the clock select logic is referred to as the timer
clock (clkT2).
The double buffered output compare register (OCR2A and OCR2B) are compared with the Timer/Counter value at all times.
The result of the compare can be used by the waveform generator to generate a PWM or variable frequency output on the
output compare pins (OC2A and OC2B). See Section 17.5 “Output Compare Unit” on page 123 for details. The compare
match event will also set the compare flag (OCF2A or OCF2B) which can be used to generate an output compare interrupt
request.
17.2.2 Definitions
Many register and bit references in this document are written in general form. A lower case “n” replaces the Timer/Counter
number, in this case 2. However, when using the register or bit defines in a program, the precise form must be used, i.e.,
TCNT2 for accessing Timer/Counter2 counter value and so on.
The definitions in Table 17-1 are also used extensively throughout the section.
Table 17-1. Definitions
Parameter
BOTTOM
MAX
Definition
The counter reaches the BOTTOM when it becomes zero (0x00).
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The
TOP value can be assigned to be the fixed value 0xFF (MAX) or the value stored in the OCR2A register.
The assignment is dependent on the mode of operation.
TOP
17.3 Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal synchronous or an external asynchronous clock source. The clock source
clkT2 is by default equal to the MCU clock, clkI/O. When the AS2 bit in the ASSR register is written to logic one, the clock
source is taken from the Timer/Counter oscillator connected to TOSC1 and TOSC2. For details on asynchronous operation,
see Section 17.11.6 “ASSR – Asynchronous Status Register” on page 136. For details on clock sources and prescaler, see
Section 17.10 “Timer/Counter Prescaler” on page 131.
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17.4 Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 17-2 shows a block diagram
of the counter and its surrounding environment.
Figure 17-2. Counter Unit Block Diagram
TOVn
(Int. Req.)
DATA BUS
TOSC1
TOSC2
T/C
Oscillator
count
clkTn
clear
TCNTn
Control Logic
Prescaler
direction
clkI/O
bottom
top
Signal description (internal signals):
count
direction
clear
Increment or decrement TCNT2 by 1.
Selects between increment and decrement.
Clear TCNT2 (set all bits to zero).
clkTn
Timer/Counter clock, referred to as clkT2 in the following.
Signalizes that TCNT2 has reached maximum value.
Signalizes that TCNT2 has reached minimum value (zero).
top
bottom
Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT2).
clkT2 can be generated from an external or internal clock source, selected by the clock select bits (CS22:0). When no clock
source is selected (CS22:0 = 0) the timer is stopped. However, the TCNT2 value can be accessed by the CPU, regardless of
whether clkT2 is present or not. A CPU write overrides (has priority over) all counter clear or count operations.
The counting sequence is determined by the setting of the WGM21 and WGM20 bits located in the Timer/Counter control
register (TCCR2A) and the WGM22 located in the Timer/Counter control register B (TCCR2B). There are close connections
between how the counter behaves (counts) and how waveforms are generated on the output compare outputs OC2A and
OC2B. For more details about advanced counting sequences and waveform generation, see Section 17.7 “Modes of
Operation” on page 125.
The Timer/Counter overflow flag (TOV2) is set according to the mode of operation selected by the WGM22:0 bits. TOV2 can
be used for generating a CPU interrupt.
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17.5 Output Compare Unit
The 8-bit comparator continuously compares TCNT2 with the output compare register (OCR2A and OCR2B). Whenever
TCNT2 equals OCR2A or OCR2B, the comparator signals a match. A match will set the output compare flag (OCF2A or
OCF2B) at the next timer clock cycle. If the corresponding interrupt is enabled, the output compare flag generates an output
compare interrupt. The output compare flag is automatically cleared when the interrupt is executed. Alternatively, the output
compare flag can be cleared by software by writing a logical one to its I/O bit location. The waveform generator uses the
match signal to generate an output according to operating mode set by the WGM22:0 bits and compare output mode
(COM2x1:0) bits. The max and bottom signals are used by the waveform generator for handling the special cases of the
extreme values in some modes of operation (see Section 17.7 “Modes of Operation” on page 125).
Figure 16-10 on page 107 shows a block diagram of the output compare unit.
Figure 17-3. Output Compare Unit, Block Diagram
DATA BUS
OCRnx
TCNTn
= (8-bit Comparator)
OCFnx (Int. Req.)
OCnx
top
bottom
FOCn
Waveform Generator
WGMn1:0
COMnX1:0
The OCR2x register is double buffered when using any of the pulse width modulation (PWM) modes. For the normal and
clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the
update of the OCR2x compare register to either top or bottom of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR2x register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has
access to the OCR2x buffer register, and if double buffering is disabled the CPU will access the OCR2x directly.
17.5.1 Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the force
output compare (FOC2x) bit. Forcing compare match will not set the OCF2x flag or reload/clear the timer, but the OC2x pin
will be updated as if a real compare match had occurred (the COM2x1:0 bits settings define whether the OC2x pin is set,
cleared or toggled).
17.5.2 Compare Match Blocking by TCNT2 Write
All CPU write operations to the TCNT2 register will block any compare match that occurs in the next timer clock cycle, even
when the timer is stopped. This feature allows OCR2x to be initialized to the same value as TCNT2 without triggering an
interrupt when the Timer/Counter clock is enabled.
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17.5.3 Using the Output Compare Unit
Since writing TCNT2 in any mode of operation will block all compare matches for one timer clock cycle, there are risks
involved when changing TCNT2 when using the output compare channel, independently of whether the Timer/Counter is
running or not. If the value written to TCNT2 equals the OCR2x value, the compare match will be missed, resulting in
incorrect waveform generation. Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is
downcounting.
The setup of the OC2x should be performed before setting the data direction register for the port pin to output. The easiest
way of setting the OC2x value is to use the force output compare (FOC2x) strobe bit in normal mode. The OC2x register
keeps its value even when changing between waveform generation modes.
Be aware that the COM2x1:0 bits are not double buffered together with the compare value. Changing the COM2x1:0 bits will
take effect immediately.
17.6 Compare Match Output Unit
The compare output mode (COM2x1:0) bits have two functions. The waveform generator uses the COM2x1:0 bits for
defining the output compare (OC2x) state at the next compare match. Also, the COM2x1:0 bits control the OC2x pin output
source. Figure 17-4 shows a simplified schematic of the logic affected by the COM2x1:0 bit setting. The I/O registers,
I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O port control registers (DDR and PORT)
that are affected by the COM2x1:0 bits are shown. When referring to the OC2x state, the reference is for the internal
OC2x register, not the OC2x pin.
Figure 17-4. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCnx
Waveform
Generator
D
D
Q
Q
1
0
OCnx
Pin
OCnx
PORT
D
Q
DDR
clkI/O
The general I/O port function is overridden by the output compare (OC2x) from the waveform generator if either of the
COM2x1:0 bits are set. However, the OC2x pin direction (input or output) is still controlled by the data direction register
(DDR) for the port pin. The data direction register bit for the OC2x pin (DDR_OC2x) must be set as output before the OC2x
value is visible on the pin. The port override function is independent of the waveform generation mode.
The design of the output compare pin logic allows initialization of the OC2x state before the output is enabled. Note that
some COM2x1:0 bit settings are reserved for certain modes of operation.
See Section 17.11 “Register Description” on page 132.
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17.6.1 Compare Output Mode and Waveform Generation
The waveform generator uses the COM2x1:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the
COM2x1:0 = 0 tells the waveform generator that no action on the OC2x register is to be performed on the next compare
match. For compare output actions in the non-PWM modes refer to Table 17-5 on page 133. For fast PWM mode, refer to
Table 17-6 on page 133, and for phase correct PWM refer to Table 17-7 on page 134.
A change of the COM2x1:0 bits state will have effect at the first compare match after the bits are written. For non-PWM
modes, the action can be forced to have immediate effect by using the FOC2x strobe bits.
17.7 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the output compare pins, is defined by the combination of
the waveform generation mode (WGM22:0) and compare output mode (COM2x1:0) bits. The compare output mode bits do
not affect the counting sequence, while the waveform generation mode bits do. The COM2x1:0 bits control whether the
PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM2x1:0 bits
control whether the output should be set, cleared, or toggled at a compare match (see Section 17.6 “Compare Match Output
Unit” on page 124).
For detailed timing information refer to Section 17.8 “Timer/Counter Timing Diagrams” on page 129.
17.7.1 Normal Mode
The simplest mode of operation is the normal mode (WGM22:0 = 0). In this mode the counting direction is always up
(incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 8-bit value
(TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the Timer/Counter overflow flag (TOV2) will be
set in the same timer clock cycle as the TCNT2 becomes zero. The TOV2 flag in this case behaves like a ninth bit, except
that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV2 flag,
the timer resolution can be increased by software. There are no special cases to consider in the normal mode, a new counter
value can be written anytime.
The output compare unit can be used to generate interrupts at some given time. Using the output compare to generate
waveforms in normal mode is not recommended, since this will occupy too much of the CPU time.
17.7.2 Clear Timer on Compare Match (CTC) Mode
In clear timer on compare or CTC mode (WGM22:0 = 2), the OCR2A register is used to manipulate the counter resolution. In
CTC mode the counter is cleared to zero when the counter value (TCNT2) matches the OCR2A. The OCR2A defines the top
value for the counter, hence also its resolution. This mode allows greater control of the compare match output frequency. It
also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Table 17-5 on page 125. The counter value (TCNT2) increases until a
compare match occurs between TCNT2 and OCR2A, and then counter (TCNT2) is cleared.
Figure 17-5. CTC Mode, Timing Diagram
OCnx Interrupt
Flag Set
TCNTn
OCnx
(COMnx1:0 = 1)
(Toggle)
1
2
3
4
Period
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An interrupt can be generated each time the counter value reaches the TOP value by using the OCF2A flag. If the interrupt
is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing TOP to a value close to
BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does
not have the double buffering feature. If the new value written to OCR2A is lower than the current value of TCNT2, the
counter will miss the compare match. The counter will then have to count to its maximum value (0xFF) and wrap around
starting at 0x00 before the compare match can occur.
For generating a waveform output in CTC mode, the OC2A output can be set to toggle its logical level on each compare
match by setting the compare output mode bits to toggle mode (COM2A1:0 = 1). The OC2A value will not be visible on the
port pin unless the data direction for the pin is set to output. The waveform generated will have a maximum frequency of
f
OC2A = fclk_I/O/2 when OCR2A is set to zero (0x00). The waveform frequency is defined by the following equation:
f
clk_I/O
------------------------------------------------
f
=
OCnx
2 N (1 + OCRnx)
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
As for the normal mode of operation, the TOV2 flag is set in the same timer clock cycle that the counter counts from MAX to
0x00.
17.7.3 Fast PWM Mode
The fast pulse width modulation or fast PWM mode (WGM22:0 = 3 or 7) provides a high frequency PWM waveform
generation option. The fast PWM differs from the other PWM option by its single-slope operation. The counter counts from
BOTTOM to TOP then restarts from BOTTOM. TOP is defined as 0xFF when WGM22:0 = 3, and OCR2A when
MGM22:0 = 7. In non-inverting compare output mode, the output compare (OC2x) is cleared on the compare match between
TCNT2 and OCR2x, and set at BOTTOM. In inverting compare output mode, the output is set on compare match and
cleared at BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high
as the phase correct PWM mode that uses dual-slope operation. This high frequency makes the fast PWM mode well suited
for power regulation, rectification, and DAC applications. High frequency allows physically small sized external components
(coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value. The counter is then cleared at
the following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure 17-6. The TCNT2 value is in
the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNT2 slopes represent compare matches between OCR2x
and TCNT2.
Figure 17-6. Fast PWM Mode, Timing Diagram
OCRnx Interrupt
Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
TCNTn
(COMnx1:0 = 2)
OCnx
OCnx
(COMnx1:0 = 3)
1
2
3
4
5
6
7
Period
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The Timer/Counter overflow flag (TOV2) is set each time the counter reaches TOP. If the interrupt is enabled, the interrupt
handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC2x pin. Setting the COM2x1:0 bits to
two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM2x1:0 to three. TOP
is defined as 0xFF when WGM2:0 = 3, and OCR2A when WGM2:0 = 7 (See Table 17-3 on page 132). The actual OC2x
value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated
by setting (or clearing) the OC2x register at the compare match between OCR2x and TCNT2, and clearing (or setting) the
OC2x register at the timer clock cycle the counter is cleared (changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f
clk_I/O
----------------
f
=
OCnxPWM
N 256
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A register represent special cases when generating a PWM waveform output in the fast
PWM mode. If the OCR2A is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle.
Setting the OCR2A equal to MAX will result in a constantly high or low output (depending on the polarity of the output set by
the COM2A1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC2x to toggle its logical
level on each compare match (COM2x1:0 = 1). The waveform generated will have a maximum frequency of foc2 = fclk_I/O/2
when OCR2A is set to zero. This feature is similar to the OC2A toggle in CTC mode, except the double buffer feature of the
output compare unit is enabled in the fast PWM mode.
17.7.4 Phase Correct PWM Mode
The phase correct PWM mode (WGM22:0 = 1 or 5) provides a high resolution phase correct PWM waveform generation
option. The phase correct PWM mode is based on a dual-slope operation. The counter counts repeatedly from BOTTOM to
TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM22:0 = 1, and OCR2A when MGM22:0 = 5. In
non-inverting compare output mode, the output compare (OC2x) is cleared on the compare match between TCNT2 and
OCR2x while upcounting, and set on the compare match while downcounting. In inverting output compare mode, the
operation is inverted. The dual-slope operation has lower maximum operation frequency than single slope operation.
However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP. When the counter reaches
TOP, it changes the count direction. The TCNT2 value will be equal to TOP for one timer clock cycle. The timing diagram for
the phase correct PWM mode is shown on Figure 17-7 on page 128. The TCNT2 value is in the timing diagram shown as a
histogram for illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small
horizontal line marks on the TCNT2 slopes represent compare matches between OCR2x and TCNT2.
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Figure 17-7. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt
Flag Set
OCRnx Update
TOVn Interrupt
Flag Set
TCNTn
(COMnx1:0 = 2)
OCnx
OCnx
(COMnx1:0 = 3)
1
2
3
Period
The Timer/Counter overflow flag (TOV2) is set each time the counter reaches BOTTOM. The interrupt flag can be used to
generate an interrupt each time the counter reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC2x pin. Setting the
COM2x1:0 bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by setting the
COM2x1:0 to three. TOP is defined as 0xFF when WGM2:0 = 3, and OCR2A when MGM2:0 = 7 (see Table 17-4 on page
133). The actual OC2x value will only be visible on the port pin if the data direction for the port pin is set as output.
The PWM waveform is generated by clearing (or setting) the OC2x register at the compare match between OCR2x and
TCNT2 when the counter increments, and setting (or clearing) the OC2x register at compare match between OCR2x and
TCNT2 when the counter decrements. The PWM frequency for the output when using phase correct PWM can be calculated
by the following equation:
f
clk_I/O
----------------
f
=
OCnxPCPWM
N 510
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A register represent special cases when generating a PWM waveform output in the phase
correct PWM mode. If the OCR2A is set equal to BOTTOM, the output will be continuously low and if set equal to MAX the
output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic
values.
At the very start of period 2 in Figure 17-7 OCnx has a transition from high to low even though there is no compare match.
The point of this transition is to guarantee symmetry around BOTTOM. There are two cases that give a transition without
compare match.
●
OCR2A changes its value from MAX, like in Figure 17-7. When the OCR2A value is MAX the OCn pin value is the
same as the result of a down-counting compare match. To ensure symmetry around BOTTOM the OCn value at MAX
must correspond to the result of an up-counting compare match.
●
The timer starts counting from a value higher than the one in OCR2A, and for that reason misses the compare match
and hence the OCn change that would have happened on the way up.
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17.8 Timer/Counter Timing Diagrams
The following figures show the Timer/Counter in synchronous mode, and the timer clock (clkT2) is therefore shown as a clock
enable signal. In asynchronous mode, clkI/O should be replaced by the Timer/Counter oscillator clock. The figures include
information on when interrupt flags are set. Figure 17-8 contains timing data for basic Timer/Counter operation. The figure
shows the count sequence close to the MAX value in all modes other than phase correct PWM mode.
Figure 17-8. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O/1)
TCNTn
TOVn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
BOTTOM + 1
OCRnx + 2
Figure 17-9 shows the same timing data, but with the prescaler enabled.
Figure 17-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
TOVn
MAX - 1
MAX
BOTTOM
Figure 17-10 shows the setting of OCF2A in all modes except CTC mode.
Figure 17-10. Timer/Counter Timing Diagram, Setting of OCF2A, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx
OCFnx
OCRnx Value
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Figure 17-11 shows the setting of OCF2A and the clearing of TCNT2 in CTC mode.
Figure 17-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
(CTC)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
OCRnx
TOP
OCFnx
17.9 Asynchronous Operation of Timer/Counter2
When Timer/Counter2 operates asynchronously, some considerations must be taken.
●
Warning: When switching between asynchronous and synchronous clocking of Timer/Counter2, the timer registers
TCNT2, OCR2x, and TCCR2x might be corrupted. A safe procedure for switching clock source is:
1. Disable the Timer/Counter2 interrupts by clearing OCIE2x and TOIE2.
2. Select clock source by setting AS2 as appropriate.
3. Write new values to TCNT2, OCR2x, and TCCR2x.
4. To switch to asynchronous operation: Wait for TCN2UB, OCR2xUB, and TCR2xUB.
5. Clear the Timer/Counter2 interrupt flags.
6. Enable interrupts, if needed.
●
●
The CPU main clock frequency must be more than four times the oscillator frequency.
When writing to one of the registers TCNT2, OCR2x, or TCCR2x, the value is transferred to a temporary register, and
latched after two positive edges on TOSC1. The user should not write a new value before the contents of the
temporary register have been transferred to its destination. Each of the five mentioned registers have their individual
temporary register, which means that e.g. writing to TCNT2 does not disturb an OCR2x write in progress. To detect
that a transfer to the destination register has taken place, the Asynchronous status register – ASSR has been
implemented.
●
●
When entering power-save or ADC noise reduction mode after having written to TCNT2, OCR2x, or TCCR2x, the
user must wait until the written register has been updated if Timer/Counter2 is used to wake up the device. Otherwise,
the MCU will enter sleep mode before the changes are effective. This is particularly important if any of the output
compare2 interrupt is used to wake up the device, since the output compare function is disabled during writing to
OCR2x or TCNT2. If the write cycle is not finished, and the MCU enters sleep mode before the corresponding
OCR2xUB bit returns to zero, the device will never receive a compare match interrupt, and the MCU will not wake up.
If Timer/Counter2 is used to wake the device up from power-save or ADC noise reduction mode, precautions must be
taken if the user wants to re-enter one of these modes: The interrupt logic needs one TOSC1 cycle to be reset. If the
time between wake-up and re-entering sleep mode is less than one TOSC1 cycle, the interrupt will not occur, and the
device will fail to wake up. If the user is in doubt whether the time before re-entering power-save or ADC noise
reduction mode is sufficient, the following algorithm can be used to ensure that one TOSC1 cycle has elapsed:
1. Write a value to TCCR2x, TCNT2, or OCR2x.
2. Wait until the corresponding update busy flag in ASSR returns to zero.
3. Enter power-save or ADC noise reduction mode.
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●
When the asynchronous operation is selected, the 32.768kHz oscillator for Timer/Counter2 is always running, except
in power-down and Standby modes. After a power-up reset or wake-up from power-down or standby mode, the user
should be aware of the fact that this oscillator might take as long as one second to stabilize. The user is advised to
wait for at least one second before using Timer/Counter2 after power-up or wake-up from power-down or standby
mode. The contents of all Timer/Counter2 registers must be considered lost after a wake-up from power-down or
standby mode due to unstable clock signal upon start-up, no matter whether the oscillator is in use or a clock signal is
applied to the TOSC1 pin.
●
●
Description of wake up from power-save or ADC noise reduction mode when the timer is clocked asynchronously:
When the interrupt condition is met, the wake up process is started on the following cycle of the timer clock, that is,
the timer is always advanced by at least one before the processor can read the counter value. After wake-up, the
MCU is halted for four cycles, it executes the interrupt routine, and resumes execution from the instruction following
SLEEP.
Reading of the TCNT2 register shortly after wake-up from power-save may give an incorrect result. Since TCNT2 is
clocked on the asynchronous TOSC clock, reading TCNT2 must be done through a register synchronized to the
internal I/O clock domain. Synchronization takes place for every rising TOSC1 edge. When waking up from
power-save mode, and the I/O clock (clkI/O) again becomes active, TCNT2 will read as the previous value (before
entering sleep) until the next rising TOSC1 edge. The phase of the TOSC clock after waking up from power-save
mode is essentially unpredictable, as it depends on the wake-up time. The recommended procedure for reading
TCNT2 is thus as follows:
1. Write any value to either of the registers OCR2x or TCCR2x.
2. Wait for the corresponding update busy flag to be cleared.
3. Read TCNT2.
●
During asynchronous operation, the synchronization of the interrupt flags for the asynchronous timer takes
3 processor cycles plus one timer cycle. The timer is therefore advanced by at least one before the processor can
read the timer value causing the setting of the interrupt flag. The output compare pin is changed on the timer clock
and is not synchronized to the processor clock.
17.10 Timer/Counter Prescaler
Figure 17-12.Prescaler for Timer/Counter2
clkI/O
clkT2S
10-bit T/C Prescaler
Clear
TOSC1
AS2
PSRASY
0
CS20
CS21
CS22
Timer/Counter2 Clock Source
clkT2
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The clock source for Timer/Counter2 is named clkT2S. clkT2S is by default connected to the main system I/O clock clkIO. By
setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously clocked from the TOSC1 pin. This enables use of
Timer/Counter2 as a real time counter (RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from port C. A
crystal can then be connected between the TOSC1 and TOSC2 pins to serve as an independent clock source for
Timer/Counter2. The oscillator is optimized for use with a 32.768kHz crystal. By setting the EXCLK bit in the ASSR a 32kHz
external clock can be applied. See Section 17.11.6 “ASSR – Asynchronous Status Register” on page 136 for details.
For Timer/Counter2, the possible prescaled selections are: clkT2S/8, clkT2S/32, clkT2S/64, clkT2S/128, clkT2S/256, and
clkT2S/1024. Additionally, clkT2S as well as 0 (stop) may be selected. Setting the PSRASY bit in GTCCR resets the prescaler.
This allows the user to operate with a predictable prescaler.
17.11 Register Description
17.11.1 TCCR2A – Timer/Counter Control Register A
Bit
7
6
5
4
3
–
2
–
1
0
(0xB0)
COM2A1 COM2A0 COM2B1 COM2B0
WGM21 WGM20 TCCR2A
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R
0
R
0
R/W
0
R/W
0
• Bits 7:6 – COM2A1:0: Compare Match Output A Mode
These bits control the output compare pin (OC2A) behavior. If one or both of the COM2A1:0 bits are set, the OC2A output
overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)
bit corresponding to the OC2A pin must be set in order to enable the output driver.
When OC2A is connected to the pin, the function of the COM2A1:0 bits depends on the WGM22:0 bit setting. Table 17-2
shows the COM2A1:0 bit functionality when the WGM22:0 bits are set to a normal or CTC mode (non-PWM).
Table 17-2. Compare Output Mode, non-PWM Mode
COM2A1
COM2A0
Description
0
0
1
1
0
1
0
1
Normal port operation, OC0A disconnected.
Toggle OC2A on compare match
Clear OC2A on compare match
Set OC2A on compare match
Table 17-3 shows the COM2A1:0 bit functionality when the WGM21:0 bits are set to fast PWM mode.
Table 17-3. Compare Output Mode, Fast PWM Mode(1)
COM2A1
COM2A0
Description
0
0
Normal port operation, OC2A disconnected.
WGM22 = 0: Normal port operation, OC0A disconnected.
WGM22 = 1: Toggle OC2A on compare match.
0
1
1
1
0
1
Clear OC2A on compare match, set OC2A at BOTTOM,
(non-inverting mode).
Set OC2A on compare match, clear OC2A at BOTTOM,
(inverting mode).
Note:
1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the compare match is
ignored, but the set or clear is done at BOTTOM. See Section 17.7.3 “Fast PWM Mode” on page 126 for more
details.
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Table 17-4 shows the COM2A1:0 bit functionality when the WGM22:0 bits are set to phase correct PWM mode.
Table 17-4. Compare Output Mode, Phase Correct PWM Mode(1)
COM2A1
COM2A0
Description
0
0
Normal port operation, OC2A disconnected.
WGM22 = 0: Normal port operation, OC2A disconnected.
WGM22 = 1: Toggle OC2A on compare match.
0
1
1
1
0
1
Clear OC2A on compare match when up-counting. Set OC2A on compare match
when down-counting.
Set OC2A on compare match when up-counting. Clear OC2A on compare match
when down-counting.
Note:
1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 17.7.4 “Phase Correct PWM Mode” on page 127 for
more details.
• Bits 5:4 – COM2B1:0: Compare Match Output B Mode
These bits control the output compare pin (OC2B) behavior. If one or both of the COM2B1:0 bits are set, the OC2B output
overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)
bit corresponding to the OC2B pin must be set in order to enable the output driver.
When OC2B is connected to the pin, the function of the COM2B1:0 bits depends on the WGM22:0 bit setting. Table 17-5
shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to a normal or CTC mode (non-PWM).
Table 17-5. Compare Output Mode, non-PWM Mode
COM2B1
COM2B0
Description
0
0
1
1
0
1
0
1
Normal port operation, OC2B disconnected.
Toggle OC2B on compare match
Clear OC2B on compare match
Set OC2B on compare match
Table 17-6 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to fast PWM mode.
Table 17-6. Compare Output Mode, Fast PWM Mode(1)
COM2B1
COM2B0
Description
0
0
0
1
Normal port operation, OC2B disconnected.
Reserved
Clear OC2B on compare match, set OC2B at BOTTOM,
(non-inverting mode).
1
1
0
1
Set OC2B on compare match, clear OC2B at BOTTOM,
(inverting mode).
Note:
1. A special case occurs when OCR2B equals TOP and COM2B1 is set. In this case, the compare match is
ignored, but the set or clear is done at BOTTOM. See Section 17.7.3 “Fast PWM Mode” on page 126 for more
details.
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Table 17-7 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to phase correct PWM mode.
Table 17-7. Compare Output Mode, Phase Correct PWM Mode(1)
COM2B1
COM2B0
Description
0
0
0
1
Normal port operation, OC2B disconnected.
Reserved
Clear OC2B on compare match when up-counting. Set OC2B on compare match
when down-counting.
1
1
0
1
Set OC2B on compare match when up-counting. Clear OC2B on compare match
when down-counting.
Note:
1. A special case occurs when OCR2B equals TOP and COM2B1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 17.7.4 “Phase Correct PWM Mode” on page 127 for
more details.
• Bits 3:2 – Reserved
These bits are reserved and will always read as zero.
• Bits 1:0 – WGM21:0: Waveform Generation Mode
Combined with the WGM22 bit found in the TCCR2B register, these bits control the counting sequence of the counter, the
source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 17-8. Modes of
operation supported by the Timer/Counter unit are: normal mode (counter), clear timer on compare match (CTC) mode, and
two types of pulse width modulation (PWM) modes (see Section 17.7 “Modes of Operation” on page 125).
Table 17-8. Waveform Generation Mode Bit Description
Timer/Counter Mode of
Mode
WGM2
WGM1
WGM0
Operation
TOP
0xFF
0xFF
OCRA
0xFF
–
Update of OCRx at TOV Flag Set on(1)(2)
0
1
2
3
4
5
6
7
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Normal
Immediate
TOP
MAX
BOTTOM
MAX
PWM, phase correct
CTC
Immediate
BOTTOM
–
Fast PWM
MAX
Reserved
–
PWM, phase correct
Reserved
OCRA
–
TOP
BOTTOM
–
–
Fast PWM
OCRA
BOTTOM
TOP
Notes: 1. MAX = 0xFF
2. BOTTOM = 0x00
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17.11.2 TCCR2B – Timer/Counter Control Register B
Bit
7
FOC2A
W
6
FOC2B
W
5
–
4
–
3
WGM22
R/W
0
2
CS22
R/W
0
1
CS21
R/W
0
0
CS20
R/W
0
(0xB1)
TCCR2B
Read/Write
Initial Value
R
0
R
0
0
0
• Bit 7 – FOC2A: Force Output Compare A
The FOC2A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR2B is written when operating
in PWM mode. When writing a logical one to the FOC2A bit, an immediate compare match is forced on the waveform
generation unit. The OC2A output is changed according to its COM2A1:0 bits setting. Note that the FOC2A bit is
implemented as a strobe. Therefore it is the value present in the COM2A1:0 bits that determines the effect of the forced
compare.
A FOC2A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR2A as TOP.
The FOC2A bit is always read as zero.
• Bit 6 – FOC2B: Force Output Compare B
The FOC2B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR2B is written when operating
in PWM mode. When writing a logical one to the FOC2B bit, an immediate compare match is forced on the waveform
generation unit. The OC2B output is changed according to its COM2B1:0 bits setting. Note that the FOC2B bit is
implemented as a strobe. Therefore it is the value present in the COM2B1:0 bits that determines the effect of the forced
compare.
A FOC2B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR2B as TOP.
The FOC2B bit is always read as zero.
• Bits 5:4 – Reserved
These bits are reserved and will always read as zero.
• Bit 3 – WGM22: Waveform Generation Mode
See the description in Section 17.11.1 “TCCR2A – Timer/Counter Control Register A” on page 132.
• Bit 2:0 – CS22:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter, see Table 17-9.
Table 17-9. Clock Select Bit Description
CS22
CS21
CS20
Description
No clock source (Timer/Counter stopped).
clkT2S/(no prescaling)
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
clkT2S/8 (from prescaler)
clkT2S/32 (From prescalerf
clkT2S/64 (from prescaler)
clkT2S/128 (from prescaler)
clkT S/256 (from prescaler)
2
clkT S/1024 (from prescaler)
2
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17.11.3 TCNT2 – Timer/Counter Register
Bit
7
6
5
4
3
2
1
0
(0xB2)
TCNT2[7:0]
R/W R/W
TCNT2
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
0
The Timer/Counter register gives direct access, both for read and write operations, to the Timer/Counter unit 8-bit counter.
Writing to the TCNT2 register blocks (removes) the compare match on the following timer clock. Modifying the counter
(TCNT2) while the counter is running, introduces a risk of missing a compare match between TCNT2 and the OCR2x
registers.
17.11.4 OCR2A – Output Compare Register A
Bit
7
6
5
4
3
2
1
0
(0xB3)
OCR2A[7:0]
R/W R/W
OCR2A
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
0
The output compare register A contains an 8-bit value that is continuously compared with the counter value (TCNT2). A
match can be used to generate an output compare interrupt, or to generate a waveform output on the OC2A pin.
17.11.5 OCR2B – Output Compare Register B
Bit
7
6
5
4
3
2
1
0
(0xB4)
OCR2B[7:0]
R/W R/W
OCR2B
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
0
The output compare register B contains an 8-bit value that is continuously compared with the counter value (TCNT2). A
match can be used to generate an output compare interrupt, or to generate a waveform output on the OC2B pin.
17.11.6 ASSR – Asynchronous Status Register
Bit
7
–
6
EXCLK
R/W
0
5
4
3
2
1
0
(0xB6)
AS2
R/W
0
TCN2UB OCR2AUB OCR2BUB TCR2AUB TCR2BUB ASSR
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R
0
R
0
• Bit 6 – EXCLK: Enable External Clock Input
When EXCLK is written to one, and asynchronous clock is selected, the external clock input buffer is enabled and an
external clock can be input on timer oscillator 1 (TOSC1) pin instead of a 32kHz crystal. Writing to EXCLK should be done
before asynchronous operation is selected. Note that the crystal oscillator will only run when this bit is zero.
• Bit 5 – AS2: Asynchronous Timer/Counter2
When AS2 is written to zero, Timer/Counter2 is clocked from the I/O clock, clkI/O. When AS2 is written to one,
Timer/Counter2 is clocked from a crystal oscillator connected to the timer oscillator 1 (TOSC1) pin. When the value of AS2 is
changed, the contents of TCNT2, OCR2A, OCR2B, TCCR2A and TCCR2B might be corrupted.
• Bit 4 – TCN2UB: Timer/Counter2 Update Busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes set. When TCNT2 has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCNT2 is
ready to be updated with a new value.
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• Bit 3 – OCR2AUB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2A is written, this bit becomes set. When OCR2A has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that OCR2A is
ready to be updated with a new value.
• Bit 2 – OCR2BUB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2B is written, this bit becomes set. When OCR2B has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that OCR2B is
ready to be updated with a new value.
• Bit 1 – TCR2AUB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2A is written, this bit becomes set. When TCCR2A has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCCR2A
is ready to be updated with a new value.
• Bit 0 – TCR2BUB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2B is written, this bit becomes set. When TCCR2B has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCCR2B
is ready to be updated with a new value.
If a write is performed to any of the five Timer/Counter2 registers while its update busy flag is set, the updated value might
get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT2, OCR2A, OCR2B, TCCR2A and TCCR2B are different. When reading TCNT2, the
actual timer value is read. When reading OCR2A, OCR2B, TCCR2A and TCCR2B the value in the temporary storage
register is read.
17.11.7 TIMSK2 – Timer/Counter2 Interrupt Mask Register
Bit
7
–
6
–
5
–
4
–
3
–
2
OCIE2B
R/W
0
1
OCIE2A
R/W
0
0
TOIE2
R/W
0
(0x70)
TIMSK2
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R
0
• Bit 2 – OCIE2B: Timer/Counter2 Output Compare Match B Interrupt Enable
When the OCIE2B bit is written to one and the I-bit in the status register is set (one), the Timer/Counter2 compare match B
interrupt is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter2 occurs, i.e., when the
OCF2B bit is set in the Timer/Counter 2 interrupt flag register – TIFR2.
• Bit 1 – OCIE2A: Timer/Counter2 Output Compare Match A Interrupt Enable
When the OCIE2A bit is written to one and the I-bit in the status register is set (one), the Timer/Counter2 compare match A
interrupt is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter2 occurs, i.e., when the
OCF2A bit is set in the Timer/Counter 2 interrupt flag register – TIFR2.
• Bit 0 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is written to one and the I-bit in the status register is set (one), the Timer/Counter2 overflow interrupt is
enabled. The corresponding interrupt is executed if an overflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in
the Timer/Counter2 interrupt flag register – TIFR2.
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17.11.8 TIFR2 – Timer/Counter2 Interrupt Flag Register
Bit
7
–
6
–
5
–
4
–
3
–
2
OCF2B
R/W
0
1
OCF2A
R/W
0
0
TOV2
R/W
0
0x17 (0x37)
Read/Write
Initial Value
TIFR2
R
0
R
0
R
0
R
0
R
0
• Bit 2 – OCF2B: Output Compare Flag 2 B
The OCF2B bit is set (one) when a compare match occurs between the Timer/Counter2 and the data in OCR2B – output
compare register2. OCF2B is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, OCF2B is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE2B (Timer/Counter2 compare
match interrupt enable), and OCF2B are set (one), the Timer/Counter2 compare match interrupt is executed.
• Bit 1 – OCF2A: Output Compare Flag 2 A
The OCF2A bit is set (one) when a compare match occurs between the Timer/Counter2 and the data in OCR2A – output
compare register2. OCF2A is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, OCF2A is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE2A (Timer/Counter2 compare
match interrupt enable), and OCF2A are set (one), the Timer/Counter2 compare match interrupt is executed.
• Bit 0 – TOV2: Timer/Counter2 Overflow Flag
The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, TOV2 is cleared by writing a logic one to the flag. When the
SREG I-bit, TOIE2A (Timer/Counter2 overflow interrupt enable), and TOV2 are set (one), the Timer/Counter2 overflow
interrupt is executed. In PWM mode, this bit is set when Timer/Counter2 changes counting direction at 0x00.
17.11.9 GTCCR – General Timer/Counter Control Register
Bit
7
6
–
5
–
4
–
3
–
2
–
1
0
0x23 (0x43)
Read/Write
Initial Value
TSM
R/W
0
PSRASY PSRSYNC GTCCR
R
0
R
0
R
0
R
0
R
0
R/W
0
R/W
0
• Bit 7 – TSM: Timer/Counter Synchronization mode
Writing the TSM bit to one, activates the Timer/Counter Synchronization mode. In this mode, the value that is written to the
PSRASY and PSRSYNC bits is kept, hence keeping the corresponding prescaler reset signals asserted. This ensures that
the corresponding Timer/Counters are halted and can be configured to the same value without the risk of one of them
advancing during configuration. When the TSM bit is written to zero, the PSRASY and PSRSYNC bits are cleared by
hardware, and the Timer/Counters start counting simultaneously.
• Bit 1 – PSRASY: Prescaler Reset Timer/Counter2
When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally cleared immediately by hardware. If the
bit is written when Timer/Counter2 is operating in asynchronous mode, the bit will remain one until the prescaler has been
reset. The bit will not be cleared by hardware if the TSM bit is set. Refer to the description of the “Bit 7 – TSM: Timer/Counter
synchronization mode” on this page for a description of the Timer/Counter synchronization mode.
• Bit 0 – PSRSYNC: Prescaler Reset
When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be reset. This bit is normally cleared immediately by
hardware, except ifthe TSM bit is set. Note that Timer/Counter1 and Timer/Counter0 share the same prescaler and a reset of
this prescaler will affect both timers.
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18. SPI – Serial Peripheral Interface
18.1 Features
●
●
●
●
●
●
●
●
Full-duplex, three-wire synchronous data transfer
Master or slave 0peration
LSB first or MSB first data transfer
Seven programmable bit rates
End of transmission interrupt flag
Write collision flag protection
Wake-up from idle mode
Double speed (CK/2) master SPI mode
18.2 Overview
The serial peripheral interface (SPI) allows high-speed synchronous data transfer between the Atmel®
ATmega164P-B/324P-B/644P-B and peripheral devices or between several AVR® devices.
USART can also be used in master SPI mode, see Section 20. “USART in SPI Mode” on page 169.
The power reduction SPI bit, PRSPI, in Section 10.12.3 “PRR0 – Power Reduction Register 0” on page 39 must be written to
zero to enable SPI module.
Figure 18-1. SPI Block Diagram(1)
S
MISO
MOSI
M
M
MSB
8-Bit Shift Register
Read Data Buffer
LSB
XTAL
S
Pin
Control
Logic
Divider
/2/4/8/16/32/64/128
Clock
SPI Clock (Master)
S
SCK
SS
Clock
Logic
Select
M
MSTR
SPE
SPI Control
8
SPI Status Register
SPI Control Register
8
8
SPI Interrupt
Request
Internal
Data Bus
Note:
1. Refer to Figure 1-1 on page 3, and Table 14-6 on page 65 for SPI pin placement.
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The interconnection between master and slave CPUs with SPI is shown in Figure 18-2. The system consists of two shift
registers, and a master clock generator. The SPI master initiates the communication cycle when pulling low the slave select
SS pin of the desired slave. master and slave prepare the data to be sent in their respective shift registers, and the master
generates the required clock pulses on the SCK line to interchange data. Data is always shifted from master to slave on the
master out – slave In, MOSI, line, and from slave to master on the master in – slave out, MISO, line. After each data packet,
the master will synchronize the slave by pulling high the slave select, SS, line.
When configured as a master, the SPI interface has no automatic control of the SS line. This must be handled by user
software before communication can start. When this is done, writing a byte to the SPI data register starts the SPI clock
generator, and the hardware shifts the eight bits into the slave. After shifting one byte, the SPI clock generator stops, setting
the end of transmission flag (SPIF). If the SPI interrupt enable bit (SPIE) in the SPCR register is set, an interrupt is
requested. The master may continue to shift the next byte by writing it into SPDR, or signal the end of packet by pulling high
the slave select, SS line. The last incoming byte will be kept in the buffer register for later use.
When configured as a slave, the SPI interface will remain sleeping with MISO tri-stated as long as the SS pin is driven high.
In this state, software may update the contents of the SPI data register, SPDR, but the data will not be shifted out by
incoming clock pulses on the SCK pin until the SS pin is driven low. As one byte has been completely shifted, the end of
transmission flag, SPIF is set. If the SPI interrupt enable bit, SPIE, in the SPCR register is set, an interrupt is requested. The
slave may continue to place new data to be sent into SPDR before reading the incoming data. The last incoming byte will be
kept in the buffer register for later use.
Figure 18-2. SPI Master-slave Interconnection
MSB MASTER
LSB
MISO
MOSI
MISO
MOSI
MSB
SLAVE
LSB
8 Bit Shift Register
8 Bit Shift Register
Shift
Enable
SCK
SS
SCK
SS
SPI
Clock Generator
The system is single buffered in the transmit direction and double buffered in the receive direction. This means that bytes to
be transmitted cannot be written to the SPI data register before the entire shift cycle is completed. When receiving data,
however, a received character must be read from the SPI data register before the next character has been completely
shifted in. Otherwise, the first byte is lost.
In SPI slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure correct sampling of the clock
signal, the minimum low and high periods should be:
Low period: longer than 2 CPU clock cycles.
High period: longer than 2 CPU clock cycles.
When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden according to Table 18-1. For
more details on automatic port overrides, refer to Section 14.3 “Alternate Port Functions” on page 62.
Table 18-1. SPI Pin Overrides(1)
Pin
MOSI
MISO
SCK
SS
Direction, Master SPI
User defined
Input
Direction, Slave SPI
Input
User defined
Input
User defined
User defined
Input
Note:
1. See Section 14.3.2 “Alternate Functions of Port B” on page 65 for a detailed description of how to define the
direction of the user defined SPI pins.
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The following code examples show how to initialize the SPI as a master and how to perform a simple transmission.
DDR_SPI in the examples must be replaced by the actual data direction register controlling the SPI pins. DD_MOSI,
DD_MISO and DD_SCK must be replaced by the actual data direction bits for these pins. E.g. if MOSI is placed on pin PB5,
replace DD_MOSI with DDB5 and DDR_SPI with DDRB.
Assembly Code Example(1)
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi
out
r17,(1<<DD_MOSI)|(1<<DD_SCK)
DDR_SPI,r17
; Enable SPI, Master, set clock rate fck/16
ldi
out
ret
r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
SPCR,r17
SPI_MasterTransmit:
; Start transmission of data (r16)
out SPDR,r16
Wait_Transmit:
; Wait for transmission complete
sbis
rjmp
ret
SPSR,SPIF
Wait_Transmit
C Code Example(1)
void SPI_MasterInit(void)
{
/* Set MOSI and SCK output, all others input */
DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);
/* Enable SPI, Master, set clock rate fck/16 */
SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);
}
void SPI_MasterTransmit(char cData)
{
/* Start transmission */
SPDR = cData;
/* Wait for transmission complete */
while(!(SPSR & (1<<SPIF)))
;
}
Note:
1. See Section 4. “About Code Examples” on page 8.
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The following code examples show how to initialize the SPI as a Slave and how to perform a simple reception.
Assembly Code Example(1)
SPI_SlaveInit:
; Set MISO output, all others input
ldi
out
r17,(1<<DD_MISO)
DDR_SPI,r17
; Enable SPI
ldi
out
ret
r17,(1<<SPE)
SPCR,r17
SPI_SlaveReceive:
; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in
r16,SPDR
ret
C Code Example(1)
void SPI_SlaveInit(void)
{
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive(void)
{
/* Wait for reception complete */
while(!(SPSR & (1<<SPIF)))
;
/* Return Data Register */
return SPDR;
}
Note:
1. See Section 4. “About Code Examples” on page 8.
18.3 SS Pin Functionality
18.3.1 Slave Mode
When the SPI is configured as a slave, the slave select (SS) pin is always input. When SS is held low, the SPI is activated,
and MISO becomes an output if configured so by the user. All other pins are inputs. When SS is driven high, all pins are
inputs, and the SPI is passive, which means that it will not receive incoming data. Note that the SPI logic will be reset once
the SS pin is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous with the master clock
generator. When the SS pin is driven high, the SPI slave will immediately reset the send and receive logic, and drop any
partially received data in the shift register.
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18.3.2 Master Mode
When the SPI is configured as a master (MSTR in SPCR is set), the user can determine the direction of the SS pin.
If SS is configured as an output, the pin is a general output pin which does not affect the SPI system. Typically, the pin will be
driving the SS pin of the SPI slave.
If SS is configured as an input, it must be held high to ensure master SPI operation. If the SS pin is driven low by peripheral
circuitry when the SPI is configured as a master with the SS pin defined as an input, the SPI system interprets this as
another master selecting the SPI as a slave and starting to send data to it. To avoid bus contention, the SPI system takes the
following actions:
1. The MSTR bit in SPCR is cleared and the SPI system becomes a slave. As a result of the SPI becoming a slave,
the MOSI and SCK pins become inputs.
2. The SPIF flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in SREG is set, the interrupt routine
will be executed.
Thus, when interrupt-driven SPI transmission is used in master mode, and there exists a possibility that SS is driven low, the
interrupt should always check that the MSTR bit is still set. If the MSTR bit has been cleared by a slave select, it must be set
by the user to re-enable SPI master mode.
18.4 Data Modes
There are four combinations of SCK phase and polarity with respect to serial data, which are determined by control bits
CPHA and CPOL. The SPI data transfer formats are shown in Figure 18-3 and Figure 18-4 on page 144. Data bits are
shifted out and latched in on opposite edges of the SCK signal, ensuring sufficient time for data signals to stabilize. This is
clearly seen by summarizing Table 18-3 and Table 18-4 on page 145, as done in Table 18-2.
Table 18-2. SPI Modes
SPI Mode
Conditions
Leading Edge
Sample (rising)
Setup (rising)
Sample (falling)
Setup (falling)
Trailing Edge
Setup (falling)
Sample (falling)
Setup (rising)
Sample (rising)
0
1
2
3
CPOL=0, CPHA=0
CPOL=0, CPHA=1
CPOL=1, CPHA=0
CPOL=1, CPHA=1
Figure 18-3. SPI Transfer Format with CPHA = 0
SCK (CPOL = 0)
mode 0
SCK (CPOL = 1)
mode 2
SAMPLE -
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SS
MSB first (DORD = 0) MSB
LSB first (DORD =1) LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
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Figure 18-4. SPI Transfer Format with CPHA = 1
SCK (CPOL = 0)
mode 1
SCK (CPOL = 1)
mode 3
SAMPLE -
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SS
MSB first (DORD = 0)
LSB first (DORD =1)
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
18.5 Register Description
18.5.1 SPCR – SPI Control Register
Bit
7
SPIE
R/W
0
6
5
DORD
R/W
0
4
MSTR
R/W
0
3
CPOL
R/W
0
2
1
0
0x2C (0x4C)
Read/Write
Initial Value
SPE
R/W
0
CPHA
R/W
0
SPR1
R/W
0
SPR0
R/W
0
SPCR
• Bit 7 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR register is set and the if the global interrupt enable bit
in SREG is set.
• Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI operations.
• Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first.
When the DORD bit is written to zero, the MSB of the data word is transmitted first.
• Bit 4 – MSTR: Master/Slave Select
This bit selects master SPI mode when written to one, and slave SPI mode when written logic zero. If SS is configured as an
input and is driven low while MSTR is set, MSTR will be cleared, and SPIF in SPSR will become set. The user will then have
to set MSTR to re-enable SPI master mode.
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• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is low when idle. Refer to Figure
18-3 on page 143 and Figure 18-4 on page 144 for an example. The CPOL functionality is summarized below:
Table 18-3. CPOL Functionality
CPOL
Leading Edge
Rising
Trailing Edge
Falling
0
1
Falling
Rising
• Bit 2 – CPHA: Clock Phase
The settings of the clock phase bit (CPHA) determine if data is sampled on the leading (first) or trailing (last) edge of SCK.
Refer to Figure 18-3 on page 143 and Figure 18-4 on page 144 for an example. The CPOL functionality is summarized
below:
Table 18-4. CPHA Functionality
CPHA
Leading Edge
Sample
Trailing Edge
Setup
0
1
Setup
Sample
• Bits 1:0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a Master. SPR1 and SPR0 have no effect on the slave. The
relationship between SCK and the oscillator clock frequency fosc is shown in the following table:
Table 18-5. Relationship Between SCK and the Oscillator Frequency
SPI2X
SPR1
SPR0
SCK Frequency
fosc/4
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
fosc/16
fosc/64
fosc/128
fosc/2
fosc/8
fosc/32
fosc/64
18.5.2 SPSR – SPI Status Register
Bit
7
SPIF
R
6
5
4
–
3
–
2
–
1
–
0
0x2D (0x4D)
Read/Write
Initial Value
WCOL
–
R
0
SPI2X
R/W
0
SPSR
R
0
R
0
R
0
R
0
R
0
0
• Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF flag is set. An interrupt is generated if SPIE in SPCR is set and global interrupts
are enabled. If SS is an input and is driven low when the SPI is in master mode, this will also set the SPIF flag. SPIF is
cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by
first reading the SPI status register with SPIF set, then accessing the SPI data register (SPDR).
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• Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI data register (SPDR) is written during a data transfer. The WCOL bit (and the SPIF bit) are
cleared by first reading the SPI status register with WCOL set, and then accessing the SPI data register.
• Bit 5:1 – Reserved
These bits are reserved and will always read as zero.
• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK frequency) will be doubled when the SPI is in master mode (see
Table 18-5 on page 145). This means that the minimum SCK period will be two CPU clock periods. When the SPI is
configured as slave, the SPI is only guaranteed to work at fosc/4 or lower.
The SPI interface on the ATmega164P-B/324P-B/644P-B is also used for program memory and EEPROM downloading or
uploading. See Section 27.8 “Serial Downloading” on page 270 for serial programming and verification.
18.5.3 SPDR – SPI Data Register
Bit
7
6
5
4
3
2
1
0
0x2E (0x4E)
Read/Write
Initial Value
MSB
R/W
X
LSB
R/W
X
SPDR
R/W
X
R/W
X
R/W
X
R/W
X
R/W
X
R/W
X
Undefined
The SPI data register is a read/write register used for data transfer between the register File and the SPI shift register.
Writing to the register initiates data transmission. Reading the register causes the shift register receive buffer to be read.
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19. USART
19.1 Features
●
●
●
●
●
●
●
●
●
●
●
●
Full duplex operation (independent serial receive and transmit registers)
Asynchronous or synchronous operation
Master or slave clocked synchronous operation
High resolution baud rate generator
Supports serial frames with 5, 6, 7, 8, or 9 data bits and 1 or 2 stop bits
Odd or even parity generation and parity check supported by hardware
Data overrun detection
Framing error detection
Noise filtering includes false start bit detection and digital low pass filter
Three separate interrupts on TX complete, TX data register empty and RX complete
Multi-processor communication mode
Double speed asynchronous communication mode
19.2 USART1 and USART0
The ATmega164P-B/324P-B/644P-B has two USART’s, USART0 and USART1.
The functionality for all USART’s is described below, most register and bit references in this section are written in general
form. A lower case “n” replaces the USART number.
USART0 and USART1 have different I/O registers as shown in Section 30. “Register Summary” on page 323.
19.3 Overview
The universal synchronous and asynchronous serial receiver and transmitter (USART) is a highly flexible serial
communication device.
A simplified block diagram of the USART transmitter is shown in Figure 19-1 on page 148. CPU accessible I/O registers and
I/O pins are shown in bold.
The power reducion USART0 bit, PRUSART0, in Section 10.12.3 “PRR0 – Power Reduction Register 0” on page 39 must be
disabled by writing a logical zero to it.
The power reducion USART1 bit, PRUSART1, in Section 10.12.4 “PRR1 – Power Reduction Register 1” on page 39 must be
disabled by writing a logical zero to it.
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Figure 19-1. USART Block Diagram(1)
Clock Generator
UBRR[H:L]
OSC
Baud Rate Generator
Sync Logic
Pin
XCK
TxD
RxD
Control
Transmitter
TX
Control
UDR (Transmit)
Parity
Generator
Pin
Control
Transmit Shift Register
Receiver
Clock
Recoverc
RX
Control
Data
Recoverc
Pin
Control
Receive Shift Register
UDR (Receive)
Parity
Checker
UCSRA
UCSRB
UCSRC
Note:
1. See Figure 1-1 on page 3 and Section 14.3 “Alternate Port Functions” on page 62 for USART pin placement.
The dashed boxes in the block diagram separate the three main parts of the USART (listed from the top): clock generator,
transmitter and receiver. Control registers are shared by all units. The clock generation logic consists of synchronization
logic for external clock input used by synchronous slave operation, and the baud rate generator. The XCKn (transfer clock)
pin is only used by synchronous transfer mode. The transmitter consists of a single write buffer, a serial shift register, parity
generator and control logic for handling different serial frame formats. The write buffer allows a continuous transfer of data
without any delay between frames. The receiver is the most complex part of the USART module due to its clock and data
recovery units. The recovery units are used for asynchronous data reception. In addition to the recovery units, the receiver
includes a parity checker, control logic, a shift register and a two level receive buffer (UDRn). The receiver supports the
same frame formats as the transmitter, and can detect frame error, data overrun and parity errors.
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19.4 Clock Generation
The clock generation logic generates the base clock for the transmitter and receiver. The USARTn supports four modes of
clock operation: normal asynchronous, double speed asynchronous, master synchronous and slave synchronous mode.
The UMSELn bit in USART control and status register C (UCSRnC) selects between asynchronous and synchronous
operation. Double speed (asynchronous mode only) is controlled by the U2Xn found in the UCSRnA register. When using
synchronous mode (UMSELn = 1), the data direction register for the XCKn pin (DDR_XCKn) controls whether the clock
source is internal (master mode) or external (slave mode). The XCKn pin is only active when using synchronous mode.
Figure 19-2 shows a block diagram of the clock generation logic.
Figure 19-2. Clock Generation Logic, Block Diagram
UBRR
U2X
fosc
UBRR+1
Prescaling
Down-Counter
/2
/4
/2
0
1
OSC
0
1
txclk
UMSEL
rxclk
DDR_XCK
Sync
Register
Edge
Detector
xcki
0
1
XCK
Pin
xcko
0
1
DDR_XCK
UCPOL
Signal description:
txclk
rxclk
xcki
xcko
fOSC
Transmitter clock (internal signal).
Receiver base clock (internal signal).
Input from XCK pin (internal signal). Used for synchronous slave operation.
Clock output to XCK pin (internal signal). Used for synchronous master operation.
XTAL pin frequency (system clock).
19.4.1 Internal Clock Generation – The Baud Rate Generator
Internal clock generation is used for the asynchronous and the synchronous master modes of operation. The description in
this section refers to Figure 19-2.
The USART baud rate register (UBRRn) and the down-counter connected to it function as a programmable prescaler or
baud rate generator. The down-counter, running at system clock (fosc), is loaded with the UBRRn value each time the
counter has counted down to zero or when the UBRRnL register is written. A clock is generated each time the counter
reaches zero. This clock is the baud rate generator clock output (= fosc/(UBRRn+1)). The transmitter divides the baud rate
generator clock output by 2, 8 or 16 depending on mode. The baud rate generator output is used directly by the receiver’s
clock and data recovery units. However, the recovery units use a state machine that uses 2, 8 or 16 states depending on
mode set by the state of the UMSELn, U2Xn and DDR_XCKn bits.
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Table 19-1 contains equations for calculating the baud rate (in bits per second) and for calculating the UBRRn value for each
mode of operation using an internally generated clock source.
Table 19-1. Equations for Calculating Baud Rate Register Setting
Operating Mode
Equation for Calculating Baud Rate(1)
Equation for Calculating UBRR Value
fOSC
fOSC
Asynchronous normal mode
(U2Xn = 0)
---------------------------------------------
----------------------
16BAUD
BAUD =
BAUD =
BAUD =
UBRRn =
UBRRn =
UBRRn =
– 1
– 1
– 1
16 × (UBRRn + 1)
fOSC
fOSC
Asynchronous double speed
mode (U2Xn = 1)
------------------------------------------
8 × (UBRRn + 1)
-------------------
8BAUD
fOSC
fOSC
------------------------------------------
2 × (UBRRn + 1)
-------------------
2BAUD
Synchronous master mode
Notes: 1. The baud rate is defined to be the transfer rate in bit per second (bps)
2. BAUD - Baud rate (in bits per second, bps)
3.
fOSC - System oscillator clock frequency
4. UBRRn - Contents of the UBRRnH and UBRRnL registers, (0-4095)
Some examples of UBRRn values for some system clock frequencies are found in Table 19-9 on page 167.
19.4.2 Double Speed Operation (U2Xn)
The transfer rate can be doubled by setting the U2Xn bit in UCSRnA. Setting this bit only has effect for the asynchronous
operation. Set this bit to zero when using synchronous operation.
Setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively doubling the transfer rate for
asynchronous communication. Note however that the Receiver will in this case only use half the number of samples
(reduced from 16 to 8) for data sampling and clock recovery, and therefore a more accurate baud rate setting and system
clock are required when this mode is used. For the transmitter, there are no downsides.
19.4.3 External Clock
External clocking is used by the synchronous slave modes of operation. The description in this section refers to Figure 19-2
on page 149 for details.
External clock input from the XCKn pin is sampled by a synchronization register to minimize the chance of meta-stability.
The output from the synchronization register must then pass through an edge detector before it can be used by the
transmitter and receiver. This process introduces a two CPU clock period delay and therefore the maximum external XCKn
clock frequency is limited by the following equation:
f
OSC
-----------
f
<
XCK
4
Note that fosc depends on the stability of the system clock source. It is therefore recommended to add some margin to avoid
possible loss of data due to frequency variations.
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19.4.4 Synchronous Clock Operation
When synchronous mode is used (UMSELn = 1), the XCKn pin will be used as either clock input (slave) or clock output
(master). The dependency between the clock edges and data sampling or data change is the same. The basic principle is
that data input (on RxDn) is sampled at the opposite XCKn clock edge of the edge the data output (TxDn) is changed.
Figure 19-3. Synchronous Mode XCKn Timing
UCPOL = 1
XCK
RxD/ TxD
Sample
Sample
UCPOL = 0
XCK
RxD/ TxD
The UCPOLn bit UCRSC selects which XCKn clock edge is used for data sampling and which is used for data change. As
Figure 19-3 shows, when UCPOLn is zero the data will be changed at rising XCKn edge and sampled at falling XCKn edge.
If UCPOLn is set, the data will be changed at falling XCKn edge and sampled at rising XCKn edge.
19.5 Frame Formats
A serial frame is defined to be one character of data bits with synchronization bits (start and stop bits), and optionally a parity
bit for error checking. The USART accepts all 30 combinations of the following as valid frame formats:
●
●
●
●
1 start bit
5, 6, 7, 8, or 9 data bits
no, even or odd parity bit
1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit. Then the next data bits, up to a total of nine, are
succeeding, ending with the most significant bit. If enabled, the parity bit is inserted after the data bits, before the stop bits.
When a complete frame is transmitted, it can be directly followed by a new frame, or the communication line can be set to an
idle (high) state. Figure 19-4 illustrates the possible combinations of the frame formats. Bits inside brackets are optional.
Figure 19-4. Frame Formats
FRAME
(IDLE)
ST
0
1
2
3
4
[5] [6] [7] [8] [P] Sp1 [Sp2] (St/ IDLE)
St
Start bit, always low.
Data bits (0 to 8).
(n)
P
Parity bit. Can be odd or even.
Stop bit, always high.
Sp
IDLE
No transfers on the communication line (RxDn or TxDn). An IDLE line must be high.
The frame format used by the USART is set by the UCSZn2:0, UPMn1:0 and USBSn bits in UCSRnB and UCSRnC. The
receiver and transmitter use the same setting. Note that changing the setting of any of these bits will corrupt all ongoing
communication for both the receiver and transmitter.
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The USART character SiZe (UCSZn2:0) bits select the number of data bits in the frame. The USART parity mode (UPMn1:0)
bits enable and set the type of parity bit. The selection between one or two stop bits is done by the USART stop bit select
(USBSn) bit. The receiver ignores the second stop bit. An FE (frame error) will therefore only be detected in the cases where
the first stop bit is zero.
19.5.1 Parity Bit Calculation
The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is used, the result of the exclusive or is
inverted. The relation between the parity bit and data bits is as follows:
P
P
= d
= d
…
…
d
d
d
d
d
d
d
d
0
1
even
n – 1
n – 1
3
3
2
2
1
1
0
0
odd
Peven
Podd
dn
Parity bit using even parity
Parity bit using odd parity
Data bit n of the character
If used, the parity bit is located between the last data bit and first stop bit of a serial frame.
19.6 USART Initialization
The USART has to be initialized before any communication can take place. The initialization process normally consists of
setting the baud rate, setting frame format and enabling the transmitter or the receiver depending on the usage. For interrupt
driven USART operation, the global interrupt flag should be cleared and the USART interrupts should be disabled.
Before doing a re-initialization with changed baud rate or frame format, be sure that there are no ongoing transmissions
during the period the registers are changed. The TXCn flag can be used to check that the transmitter has completed all
transfers, and the RXC flag can be used to check that there are no unread data in the receive buffer. Note that the TXCn flag
must be cleared before each transmission (before UDRn is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C function that are equal in
functionality. The examples assume asynchronous operation using polling (no interrupts enabled) and a fixed frame format.
The baud rate is given as a function parameter. For the assembly code, the baud rate parameter is assumed to be stored in
the r17:r16 registers.
Assembly Code Example(1)
USART_Init:
; Set baud rate
out
out
UBRRnH, r17
UBRRnL, r16
; Enable receiver and transmitter
ldi
out
r16, (1<<RXENn)|(1<<TXENn)
UCSRnB,r16
; Set frame format: 8data, 2stop bit
ldi
out
ret
r16, (1<<USBSn)|(3<<UCSZn0)
UCSRnC,r16
C Code Example(1)
void USART_Init( unsigned int baud )
{
/* Set baud rate */
UBRRnH = (unsigned char)(baud>>8);
UBRRnL = (unsigned char)baud;
/* Enable receiver and transmitter */
UCSRnB = (1<<RXENn)|(1<<TXENn);
/* Set frame format: 8data, 2stop bit */
UCSRnC = (1<<USBSn)|(3<<UCSZn0);
}
Note:
1. See Section 4. “About Code Examples” on page 8.
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More advanced initialization routines can be made that include frame format as parameters, disable interrupts and so on.
However, many applications use a fixed setting of the baud and control registers, and for these types of applications the
initialization code can be placed directly in the main routine, or be combined with initialization code for other I/O modules.
19.7 Data Transmission – The USART Transmitter
The USART transmitter is enabled by setting the transmit enable (TXEN) bit in the UCSRnB register. When the transmitter is
enabled, the normal port operation of the TxDn pin is overridden by the USART and given the function as the transmitter’s
serial output. The baud rate, mode of operation and frame format must be set up once before doing any transmissions. If
synchronous operation is used, the clock on the XCKn pin will be overridden and used as transmission clock.
19.7.1 Sending Frames with 5 to 8 Data Bit
A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The CPU can load the transmit
buffer by writing to the UDRn I/O location. The buffered data in the transmit buffer will be moved to the shift register when the
shift register is ready to send a new frame. The shift register is loaded with new data if it is in idle state (no ongoing
transmission) or immediately after the last stop bit of the previous frame is transmitted. When the shift register is loaded with
new data, it will transfer one complete frame at the rate given by the baud register, U2Xn bit or by XCKn depending on mode
of operation.
The following code examples show a simple USART transmit function based on polling of the data register empty (UDREn)
flag. When using frames with less than eight bits, the most significant bits written to the UDRn are ignored. The USART has
to be initialized before the function can be used. For the assembly code, the data to be sent is assumed to be stored in
register R16.
Assembly Code Example(1)
USART_Transmit:
; Wait for empty transmit buffer
sbis
rjmp
UCSRnA,UDREn
USART_Transmit
; Put data (r16) into buffer, sends the data
out
ret
UDRn,r16
C Code Example(1)
void USART_Transmit(unsigned char data)
{
/* Wait for empty transmit buffer */
while (!(UCSRnA & (1<<UDREn)))
;
/* Put data into buffer, sends the data */
UDRn = data;
}
Note:
1. See Section 4. “About Code Examples” on page 8.
The function simply waits for the transmit buffer to be empty by checking the UDREn flag, before loading it with new data to
be transmitted. If the data register empty interrupt is utilized, the interrupt routine writes the data into the buffer.
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19.7.2 Sending Frames with 9 Data Bit
If 9-bit characters are used (UCSZn = 7), the ninth bit must be written to the TXB8 bit in UCSRnB before the low byte of the
character is written to UDRn. The following code examples show a transmit function that handles 9-bit characters. For the
assembly code, the data to be sent is assumed to be stored in registers R17:R16.
Assembly Code Example(1)(2)
USART_Transmit:
; Wait for empty transmit buffer
sbis
rjmp
UCSRnA,UDREn
USART_Transmit
; Copy 9th bit from r17 to TXB8
cbi
sbrc
sbi
UCSRnB,TXB8
r17,0
UCSRnB,TXB8
; Put LSB data (r16) into buffer, sends the data
out
ret
UDRn,r16
C Code Example(1)(2)
void USART_Transmit(unsigned int data)
{
/* Wait for empty transmit buffer */
while (!(UCSRnA & (1<<UDREn))))
;
/* Copy 9th bit to TXB8 */
UCSRnB &= ~(1<<TXB8);
if (data & 0x0100)
UCSRnB |= (1<<TXB8);
/* Put data into buffer, sends the data */
UDRn = data;
}
Notes: 1. These transmit functions are written to be general functions. They can be optimized if the contents of the
UCSRnB is static. For example, only the TXB8 bit of the UCSRnB register is used after initialization.
2. See Section 4. “About Code Examples” on page 8.
The ninth bit can be used for indicating an address frame when using multi processor communication mode or for other
protocol handling as for example synchronization.
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19.7.3 Transmitter Flags and Interrupts
The USART transmitter has two flags that indicate its state: USART data register empty (UDREn) and transmit complete
(TXCn). Both flags can be used for generating interrupts.
The data register empty (UDREn) flag indicates whether the transmit buffer is ready to receive new data. This bit is set when
the transmit buffer is empty, and cleared when the transmit buffer contains data to be transmitted that has not yet been
moved into the shift register. For compatibility with future devices, always write this bit to zero when writing the UCSRnA
register.
When the data register empty interrupt enable (UDRIEn) bit in UCSRnB is written to one, the USART data register empty
interrupt will be executed as long as UDREn is set (provided that global interrupts are enabled). UDREn is cleared by writing
UDRn. When interrupt-driven data transmission is used, the data register empty interrupt routine must either write new data
to UDRn in order to clear UDREn or disable the data register empty interrupt, otherwise a new interrupt will occur once the
interrupt routine terminates.
The transmit complete (TXCn) flag bit is set one when the entire frame in the transmit shift register has been shifted out and
there are no new data currently present in the transmit buffer. The TXCn flag bit is automatically cleared when a transmit
complete interrupt is executed, or it can be cleared by writing a one to its bit location. The TXCn flag is useful in half-duplex
communication interfaces (like the RS-485 standard), where a transmitting application must enter receive mode and free the
communication bus immediately after completing the transmission.
When the transmit complete interrupt enable (TXCIEn) bit in UCSRnB is set, the USART transmit complete interrupt will be
executed when the TXCn flag becomes set (provided that global interrupts are enabled). When the transmit complete
interrupt is used, the interrupt handling routine does not have to clear the TXCn flag, this is done automatically when the
interrupt is executed.
19.7.4 Parity Generator
The parity generator calculates the parity bit for the serial frame data. When parity bit is enabled (UPMn1 = 1), the
transmitter control logic inserts the parity bit between the last data bit and the first stop bit of the frame that is sent.
19.7.5 Disabling the Transmitter
The disabling of the transmitter (setting the TXEN to zero) will not become effective until ongoing and pending transmissions
are completed, i.e., when the transmit shift register and transmit buffer register do not contain data to be transmitted. When
disabled, the transmitter will no longer override the TxDn pin.
19.8 Data Reception – The USART Receiver
The USART receiver is enabled by writing the receive enable (RXENn) bit in the UCSRnB register to one. When the receiver
is enabled, the normal pin operation of the RxDn pin is overridden by the USART and given the function as the receiver’s
serial input. The baud rate, mode of operation and frame format must be set up once before any serial reception can be
done. If synchronous operation is used, the clock on the XCKn pin will be used as transfer clock.
19.8.1 Receiving Frames with 5 to 8 Data Bits
The receiver starts data reception when it detects a valid start bit. Each bit that follows the start bit will be sampled at the
baud rate or XCKn clock, and shifted into the receive shift register until the first stop bit of a frame is received. A second stop
bit will be ignored by the receiver. When the first stop bit is received, i.e., a complete serial frame is present in the receive
shift register, the contents of the shift register will be moved into the receive buffer. The receive buffer can then be read by
reading the UDRn I/O location.
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The following code example shows a simple USART receive function based on polling of the receive complete (RXCn) flag.
When using frames with less than eight bits the most significant bits of the data read from the UDRn will be masked to zero.
The USART has to be initialized before the function can be used.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis
rjmp
UCSRnA, RXCn
USART_Receive
; Get and return received data from buffer
in
r16, UDRn
ret
C Code Example(1)
unsigned char USART_Receive(void)
{
/* Wait for data to be received */
while (!(UCSRnA & (1<<RXCn)))
;
/* Get and return received data from buffer */
return UDRn;
}
Note:
1. See Section 4. “About Code Examples” on page 8.
The function simply waits for data to be present in the receive buffer by checking the RXCn flag, before reading the buffer
and returning the value.
19.8.2 Receiving Frames with 9 Data Bits
If 9-bit characters are used (UCSZn=7) the ninth bit must be read from the RXB8n bit in UCSRnB before reading the low bits
from the UDRn. This rule applies to the FEn, DORn and UPEn status flags as well. Read status from UCSRnA, then data
from UDRn. Reading the UDRn I/O location will change the state of the receive buffer FIFO and consequently the TXB8n,
FEn, DORn and UPEn bits, which all are stored in the FIFO, will change.
The following code example shows a simple USART receive function that handles both nine bit characters and the status
bits.
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Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis
rjmp
UCSRnA, RXCn
USART_Receive
; Get status and 9th bit, then data from buffer
in
in
in
r18, UCSRnA
r17, UCSRnB
r16, UDRn
; If error, return -1
andi
breq
ldi
r18,(1<<FEn)|(1<<DORn)|(1<<UPEn)
USART_ReceiveNoError
r17, HIGH(-1)
r16, LOW(-1)
ldi
USART_ReceiveNoError:
; Filter the 9th bit, then return
lsr r17
andi r17, 0x01
ret
C Code Example(1)
unsigned int USART_Receive( void )
{
unsigned char status, resh, resl;
/* Wait for data to be received */
while (!(UCSRnA & (1<<RXCn)))
;
/* Get status and 9th bit, then data */
/* from buffer */
status = UCSRnA;
resh = UCSRnB;
resl = UDRn;
/* If error, return -1 */
if (status & (1<<FEn)|(1<<DORn)|(1<<UPEn))
return -1;
/* Filter the 9th bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
Note:
1. See Section 4. “About Code Examples” on page 8.
The receive function example reads all the I/O registers into the register file before any computation is done. This gives an
optimal receive buffer utilization since the buffer location read will be free to accept new data as early as possible.
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19.8.3 Receive Compete Flag and Interrupt
The USART receiver has one flag that indicates the receiver state.
The receive complete (RXCn) flag indicates if there are unread data present in the receive buffer. This flag is one when
unread data exist in the receive buffer, and zero when the receive buffer is empty (i.e., does not contain any unread data). If
the receiver is disabled (RXENn = 0), the receive buffer will be flushed and consequently the RXCn bit will become zero.
When the receive complete interrupt enable (RXCIEn) in UCSRnB is set, the USART receive Complete interrupt will be
executed as long as the RXCn flag is set (provided that global interrupts are enabled). When interrupt-driven data reception
is used, the receive complete routine must read the received data from UDRn in order to clear the RXCn flag, otherwise a
new interrupt will occur once the interrupt routine terminates.
19.8.4 Receiver Error Flags
The USART receiver has three error flags: frame error (FEn), data OverRun (DORn) and parity error (UPEn). All can be
accessed by reading UCSRnA. Common for the error flags is that they are located in the receive buffer together with the
frame for which they indicate the error status. Due to the buffering of the error flags, the UCSRnA must be read before the
receive buffer (UDRn), since reading the UDRn I/O location changes the buffer read location. Another equality for the error
flags is that they can not be altered by software doing a write to the flag location. However, all flags must be set to zero when
the UCSRnA is written for upward compatibility of future USART implementations. None of the error flags can generate
interrupts.
The frame error (FEn) flag indicates the state of the first stop bit of the next readable frame stored in the receive buffer. The
FEn flag is zero when the stop bit was correctly read (as one), and the FEn flag will be one when the stop bit was incorrect
(zero). This flag can be used for detecting out-of-sync conditions, detecting break conditions and protocol handling. The FEn
flag is not affected by the setting of the USBSn bit in UCSRnC since the receiver ignores all, except for the first, stop bits. For
compatibility with future devices, always set this bit to zero when writing to UCSRnA.
The data OverRun (DORn) flag indicates data loss due to a receiver buffer full condition. A data OverRun occurs when the
receive buffer is full (two characters), it is a new character waiting in the receive shift register, and a new start bit is detected.
If the DORn flag is set there was one or more serial frame lost between the frame last read from UDRn, and the next frame
read from UDRn. For compatibility with future devices, always write this bit to zero when writing to UCSRnA. The DORn flag
is cleared when the frame received was successfully moved from the shift register to the receive buffer.
The parity error (UPEn) flag indicates that the next frame in the receive buffer had a parity error when received. If parity
check is not enabled the UPEn bit will always be read zero. For compatibility with future devices, always set this bit to zero
when writing to UCSRnA. For more details see Section 19.5.1 “Parity Bit Calculation” on page 152 and Section 19.8.5 “Parity
Checker” on page 158.
19.8.5 Parity Checker
The parity checker is active when the high USART parity mode (UPMn1) bit is set. Type of parity check to be performed (odd
or even) is selected by the UPMn0 bit. When enabled, the parity checker calculates the parity of the data bits in incoming
frames and compares the result with the parity bit from the serial frame. The result of the check is stored in the receive buffer
together with the received data and stop bits. The parity error (UPEn) flag can then be read by software to check if the frame
had a parity error.
The UPEn bit is set if the next character that can be read from the receive buffer had a parity error when received and the
parity checking was enabled at that point (UPMn1 = 1). This bit is valid until the receive buffer (UDRn) is read.
19.8.6 Disabling the Receiver
In contrast to the transmitter, disabling of the receiver will be immediate. Data from ongoing receptions will therefore be lost.
When disabled (i.e., the RXENn is set to zero) the receiver will no longer override the normal function of the RxDn port pin.
The receiver buffer FIFO will be flushed when the receiver is disabled. Remaining data in the buffer will be lost
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19.8.7 Flushing the Receive Buffer
The receiver buffer FIFO will be flushed when the receiver is disabled, i.e., the buffer will be emptied of its contents. Unread
data will be lost. If the buffer has to be flushed during normal operation, due to for instance an error condition, read the UDRn
I/O location until the RXCn flag is cleared. The following code example shows how to flush the receive buffer.
Assembly Code Example(1)
USART_Flush:
sbis
ret
in
UCSRnA, RXCn
r16, UDRn
USART_Flush
rjmp
C Code Example(1)
void USART_Flush( void )
{
unsigned char dummy;
while (UCSRnA & (1<<RXCn)) dummy = UDRn;
}
Note:
1. See Section 4. “About Code Examples” on page 8.
19.9 Asynchronous Data Reception
The USART includes a clock recovery and a data recovery unit for handling asynchronous data reception. The clock
recovery logic is used for synchronizing the internally generated baud rate clock to the incoming asynchronous serial frames
at the RxDn pin. The data recovery logic samples and low pass filters each incoming bit, thereby improving the noise
immunity of the receiver. The asynchronous reception operational range depends on the accuracy of the internal baud rate
clock, the rate of the incoming frames, and the frame size in number of bits.
19.9.1 Asynchronous Clock Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 19-5 illustrates the sampling
process of the start bit of an incoming frame. The sample rate is 16 times the baud rate for Normal mode, and eight times the
baud rate for double speed mode. The horizontal arrows illustrate the synchronization variation due to the sampling process.
Note the larger time variation when using the Double Speed mode (U2Xn = 1) of operation. Samples denoted zero are
samples done when the RxDn line is idle (i.e., no communication activity).
Figure 19-5. Start Bit Sampling
RxD
IDLE
START
BIT 0
Sample
(U2X = 0)
0
0
0
1
1
2
3
2
4
5
3
6
7
4
8
9
5
10
11
6
12
13
7
14
15
8
16
1
1
2
3
Sample
(U2X = 1)
2
When the clock recovery logic detects a high (idle) to low (start) transition on the RxDn line, the start bit detection sequence
is initiated. Let sample 1 denote the first zero-sample as shown in the figure. The clock recovery logic then uses samples 8,
9, and 10 for normal mode, and samples 4, 5, and 6 for double speed mode (indicated with sample numbers inside boxes on
the figure), to decide if a valid start bit is received. If two or more of these three samples have logical high levels (the majority
wins), the start bit is rejected as a noise spike and the receiver starts looking for the next high to low-transition. If however, a
valid start bit is detected, the clock recovery logic is synchronized and the data recovery can begin. The synchronization
process is repeated for each start bit.
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19.9.2 Asynchronous Data Recovery
When the receiver clock is synchronized to the start bit, the data recovery can begin. The data recovery unit uses a state
machine that has 16 states for each bit in normal mode and eight states for each bit in double speed mode. Figure 19-6
shows the sampling of the data bits and the parity bit. Each of the samples is given a number that is equal to the state of the
recovery unit.
Figure 19-6. Sampling of Data and Parity Bit
RxD
Bit n
Sample
(U2X = 0)
1
1
2
3
2
4
5
3
6
7
4
8
9
10
11
6
12
13
7
14
15
8
16
1
1
Sample
(U2X = 1)
5
The decision of the logic level of the received bit is taken by doing a majority voting of the logic value to the three samples in
the center of the received bit. The center samples are emphasized on the figure by having the sample number inside boxes.
The majority voting process is done as follows: If two or all three samples have high levels, the received bit is registered to
be a logic 1. If two or all three samples have low levels, the received bit is registered to be a logic 0. This majority voting
process acts as a low pass filter for the incoming signal on the RxDn pin. The recovery process is then repeated until a
complete frame is received. Including the first stop bit. Note that the receiver only uses the first stop bit of a frame.
Figure 19-7 shows the sampling of the stop bit and the earliest possible beginning of the start bit of the next frame.
Figure 19-7. Stop Bit Sampling and Next Start Bit Sampling
RxD
(A)
(B)
(C)
STOP 1
Sample
(U2X = 0)
1
1
2
3
2
4
5
3
6
7
4
8
9
5
10
0/1 0/1 0/1
Sample
(U2X = 1)
6
0/1
The same majority voting is done to the stop bit as done for the other bits in the frame. If the stop bit is registered to have a
logic 0 value, the frame error (FEn) flag will be set.
A new high to low transition indicating the start bit of a new frame can come right after the last of the bits used for majority
voting. For normal speed mode, the first low level sample can be at point marked (A) in Figure 19-7. For double speed mode
the first low level must be delayed to (B). (C) marks a stop bit of full length. The early start bit detection influences the
operational range of the receiver.
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19.9.3 Asynchronous Operational Range
The operational range of the receiver is dependent on the mismatch between the received bit rate and the internally
generated baud rate. If the transmitter is sending frames at too fast or too slow bit rates, or the internally generated baud rate
of the receiver does not have a similar (see Table 19-2 on page 161) base frequency, the receiver will not be able to
synchronize the frames to the start bit.
The following equations can be used to calculate the ratio of the incoming data rate and internal receiver baud rate.
(D + 1) × S
S – 1 + D × S + SF
(D + 2) × S
(D + 1) × S + SM
--------------------------------------------
-----------------------------------------
Rfast =
Rslow
=
D
S
Sum of character size and parity size (D = 5 to 10 bit)
Samples per bit. S = 16 for normal speed mode and S = 8 for double speed
mode.
SF
First sample number used for majority voting. SF = 8 for normal speed and SF = 4
for double speed mode.
SM
Middle sample number used for majority voting. SM = 9 for normal speed and
SM = 5 for double speed mode.
Rslow
is the ratio of the slowest incoming data rate that can be accepted in relation to the
receiver baud rate. Rfast is the ratio of the fastest incoming data rate that can be
accepted in relation to the receiver baud rate.
Table 19-2 and Table 19-3 list the maximum receiver baud rate error that can be tolerated. Note that normal speed mode has
higher toleration of baud rate variations.
Table 19-2. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode (U2Xn = 0)
Recommended Max Receiver
D# (Data+Parity Bit)
Rslow (%)
93.20
94.12
94.81
95.36
95.81
96.17
Rfast (%)
106.67
105.79
105.11
104.58
104.14
103.78
Max Total Error (%)
Error (%)
5
6
+6.67/–6.8
±3.0
+5.79/–5.88
+5.11/–5.19
+4.58/–4.54
+4.14/–4.19
+3.78/–3.83
±2.5
7
±2.0
8
±2.0
9
±1.5
10
±1.5
Table 19-3. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode (U2Xn = 1)
Recommended Max Receiver
D# (Data+Parity Bit)
Rslow (%)
94.12
94.92
95.52
96.00
96.39
96.70
Rfast (%)
105.66
104.92
104,35
103.90
103.53
103.23
Max Total Error (%)
Error (%)
5
6
+5.66/–5.88
±2.5
+4.92/–5.08
±2.0
7
+4.35/–4.48
±1.5
8
+3.90/–4.00
±1.5
9
+3.53/–3.61
±1.5
10
+3.23/–3.30
±1.0
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The recommendations of the maximum receiver baud rate error was made under the assumption that the receiver and
transmitter equally divides the maximum total error.
There are two possible sources for the receivers baud rate error. The receiver’s system clock (XTAL) will always have some
minor instability over the supply voltage range and the temperature range. When using a crystal to generate the system
clock, this is rarely a problem, but for a resonator the system clock may differ more than 2% depending of the resonators
tolerance. The second source for the error is more controllable. The baud rate generator can not always do an exact division
of the system frequency to get the baud rate wanted. In this case an UBRR value that gives an acceptable low error can be
used if possible.
19.10 Multi-processor Communication Mode
Setting the multi-processor communication mode (MPCMn) bit in UCSRnA enables a filtering function of incoming frames
received by the USART receiver. Frames that do not contain address information will be ignored and not put into the receive
buffer. This effectively reduces the number of incoming frames that has to be handled by the CPU, in a system with multiple
MCUs that communicate via the same serial bus. The transmitter is unaffected by the MPCMn setting, but has to be used
differently when it is a part of a system utilizing the multi-processor communication mode.
If the receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop bit indicates if the frame contains
data or address information. If the receiver is set up for frames with nine data bits, then the ninth bit (RXB8n) is used for
identifying address and data frames. When the frame type bit (the first stop or the ninth bit) is one, the frame contains an
address. When the frame type bit is zero the frame is a data frame.
The multi-processor communication mode enables several slave MCUs to receive data from a master MCU. This is done by
first decoding an address frame to find out which MCU has been addressed. If a particular slave MCU has been addressed,
it will receive the following data frames as normal, while the other slave MCUs will ignore the received frames until another
address frame is received.
19.10.1 Using MPCMn
For an MCU to act as a master MCU, it can use a 9-bit character frame format (UCSZn = 7). The ninth bit (TXB8n) must be
set when an address frame (TXB8n = 1) or cleared when a data frame (TXB = 0) is being transmitted. The slave MCUs must
in this case be set to use a 9-bit character frame format.
The following procedure should be used to exchange data in multi-processor communication mode:
1. All slave MCUs are in multi-processor communication mode (MPCMn in UCSRnA is set).
2. The master MCU sends an address frame, and all slaves receive and read this frame. In the slave MCUs, the
RXCn Flag in UCSRnA will be set as normal.
3. Each slave MCU reads the UDRn register and determines if it has been selected. If so, it clears the MPCMn bit in
UCSRnA, otherwise it waits for the next address byte and keeps the MPCMn setting.
4. The addressed MCU will receive all data frames until a new address frame is received. The other slave MCUs,
which still have the MPCMn bit set, will ignore the data frames.
5. When the last data frame is received by the addressed MCU, the addressed MCU sets the MPCMn bit and waits
for a new address frame from master. The process then repeats from 2.
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the receiver must change between
using n and n+1 character frame formats. This makes full-duplex operation difficult since the transmitter and receiver uses
the same character size setting. If 5- to 8-bit character frames are used, the transmitter must be set to use two stop bit
(USBSn = 1) since the first stop bit is used for indicating the frame type.
Do not use read-modify-write instructions (SBI and CBI) to set or clear the MPCMn bit. The MPCMn bit shares the same I/O
location as the TXCn flag and this might accidentally be cleared when using SBI or CBI instructions.
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19.11 Register Description
19.11.1 UDRn – USART I/O Data Register n
Bit
7
6
5
4
3
2
1
0
RXB[7:0]
TXB[7:0]
UDRn (Read)
UDRn (Write)
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
The USART transmit data buffer register and USART receive data buffer registers share the same I/O address referred to as
USART data register or UDRn. The transmit data buffer register (TXB) will be the destination for data written to the UDRn
register location. Reading the UDRn register location will return the contents of the receive data buffer register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the transmitter and set to zero by the receiver.
The transmit buffer can only be written when the UDREn flag in the UCSRnA register is set. Data written to UDRn when the
UDREn flag is not set, will be ignored by the USART transmitter. When data is written to the transmit buffer, and the
transmitter is enabled, the transmitter will load the data into the transmit shift register when the shift register is empty. Then
the data will be serially transmitted on the TxDn pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever the receive buffer is accessed. Due
to this behavior of the receive buffer, do not use read-modify-write instructions (SBI and CBI) on this location. Be careful
when using bit test instructions (SBIC and SBIS), since these also will change the state of the FIFO.
19.11.2 UCSRnA – USART Control and Status Register A
Bit
7
RXCn
R
6
TXCn
R/W
0
5
4
FEn
R
3
DORn
R
2
UPEn
R
1
U2Xn
R/W
0
0
UDREn
MPCMn UCSRnA
Read/Write
Initial Value
R
1
R/W
0
0
0
0
0
• Bit 7 – RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive buffer is empty (i.e., does
not contain any unread data). If the receiver is disabled, the receive buffer will be flushed and consequently the RXCn bit will
become zero. The RXCn flag can be used to generate a receive complete interrupt (see description of the RXCIEn bit).
• Bit 6 – TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the transmit shift register has been shifted out and there are no new data currently
present in the transmit buffer (UDRn). The TXCn flag bit is automatically cleared when a transmit complete interrupt is
executed, or it can be cleared by writing a one to its bit location. The TXCn flag can generate a transmit complete interrupt
(see description of the TXCIEn bit).
• Bit 5 – UDREn: USART Data Register Empty
The UDREn flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREn is one, the buffer is empty,
and therefore ready to be written. The UDREn flag can generate a data register empty interrupt (see description of the
UDRIEn bit).UDREn is set after a reset to indicate that the transmitter is ready.
• Bit 4 – FEn: Frame Error
This bit is set if the next character in the receive buffer had a frame error when received. I.e., when the first stop bit of the
next character in the receive buffer is zero. This bit is valid until the receive buffer (UDRn) is read. The FEn bit is zero when
the stop bit of received data is one. Always set this bit to zero when writing to UCSRnA.
• Bit 3 – DORn: Data OverRun
This bit is set if a data overrun condition is detected. A data overrun occurs when the receive buffer is full (two characters), it
is a new character waiting in the receive shift register, and a new start bit is detected. This bit is valid until the receive buffer
(UDRn) is read. Always set this bit to zero when writing to UCSRnA.
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• Bit 2 – UPEn: USART Parity Error
This bit is set if the next character in the receive buffer had a parity error when received and the parity checking was enabled
at that point (UPMn1 = 1). This bit is valid until the receive buffer (UDRn) is read. Always set this bit to zero when writing to
UCSRnA.
• Bit 1 – U2Xn: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using synchronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively doubling the transfer rate for
asynchronous communication.
• Bit 0 – MPCMn: Multi-processor Communication Mode
This bit enables the multi-processor communication mode. When the MPCMn bit is written to one, all the incoming frames
received by the USART receiver that do not contain address information will be ignored. The transmitter is unaffected by the
MPCMn setting. For more detailed information see Section 19.10 “Multi-processor Communication Mode” on page 162.
19.11.3 UCSRnB – USART Control and Status Register n B
Bit
7
RXCIEn
R/W
0
6
TXCIEn
R/W
0
5
UDRIEn
R/W
0
4
RXENn
R/W
0
3
TXENn
R/W
0
2
UCSZn2
R/W
1
0
TXB8n
R/W
0
RXB8n
UCSRnB
Read/Write
Initial Value
R
0
0
• Bit 7 – RXCIEn: RX Complete Interrupt Enable n
Writing this bit to one enables interrupt on the RXCn flag. A USART receive complete interrupt will be generated only if the
RXCIEn bit is written to one, the global interrupt flag in SREG is written to one and the RXCn bit in UCSRnA is set.
• Bit 6 – TXCIEn: TX Complete Interrupt Enable n
Writing this bit to one enables interrupt on the TXCn flag. A USART transmit complete interrupt will be generated only if the
TXCIEn bit is written to one, the global interrupt flag in SREG is written to one and the TXCn bit in UCSRnA is set.
• Bit 5 – UDRIEn: USART Data Register Empty Interrupt Enable n
Writing this bit to one enables interrupt on the UDREn flag. A data register empty interrupt will be generated only if the
UDRIEn bit is written to one, the global interrupt flag in SREG is written to one and the UDREn bit in UCSRnA is set.
• Bit 4 – RXENn: Receiver Enable n
Writing this bit to one enables the USART receiver. The receiver will override normal port operation for the RxDn pin when
enabled. Disabling the receiver will flush the receive buffer invalidating the FEn, DORn, and UPEn flags.
• Bit 3 – TXENn: Transmitter Enable n
Writing this bit to one enables the USART transmitter. The transmitter will override normal port operation for the TxDn pin
when enabled. The disabling of the transmitter (writing TXENn to zero) will not become effective until ongoing and pending
transmissions are completed, i.e., when the transmit shift register and transmit buffer register do not contain data to be
transmitted. When disabled, the transmitter will no longer override the TxDn port.
• Bit 2 – UCSZn2: Character Size n
The UCSZn2 bits combined with the UCSZn1:0 bit in UCSRnC sets the number of data bits (character size) in a frame the
receiver and transmitter use.
• Bit 1 – RXB8n: Receive Data Bit 8 n
RXB8n is the ninth data bit of the received character when operating with serial frames with nine data bits. Must be read
before reading the low bits from UDRn.
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• Bit 0 – TXB8n: Transmit Data Bit 8 n
TXB8n is the ninth data bit in the character to be transmitted when operating with serial frames with nine data bits. Must be
written before writing the low bits to UDRn.
19.11.4 UCSRnC – USART Control and Status Register n C
Bit
7
6
5
4
3
2
1
0
UMSELn1 UMSELn0 UPMn1 UPMn0 USBSn UCSZn1 UCSZn0 UCPOLn UCSRnC
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
1
R/W
1
R/W
0
• Bits 7:6 – UMSELn1:0 USART Mode Select
These bits select the mode of operation of the USARTn as shown in Table 19-4.
Table 19-4. UMSELn Bits Settings
UMSELn1
UMSELn0
Mode
0
0
1
1
0
1
0
1
Asynchronous USART
Synchronous USART
(Reserved)
Master SPI (MSPIM)(1)
Note:
1. See Section 20. “USART in SPI Mode” on page 169 for full description of the master SPI mode (MSPIM)
operation.
• Bits 5:4 – UPMn1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the transmitter will automatically generate and
send the parity of the transmitted data bits within each frame. The receiver will generate a parity value for the incoming data
and compare it to the UPMn setting. If a mismatch is detected, the UPEn flag in UCSRnA will be set.
Table 19-5. UPMn Bits Settings
UPMn1
UPMn0
Parity Mode
Disabled
0
0
1
1
0
1
0
1
Reserved
Enabled, even parity
Enabled, odd parity
• Bit 3 – USBSn: Stop Bit Select
This bit selects the number of stop bits to be inserted by the transmitter. The receiver ignores this setting.
Table 19-6. USBS Bit Settings
USBSn
Stop Bit(s)
1-bit
0
1
2-bit
• Bit 2:1 – UCSZn1:0: Character Size
The UCSZn1:0 bits combined with the UCSZn2 bit in UCSRnB sets the number of data bits (character size) in a frame the
receiver and transmitter use.
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Table 19-7. UCSZn Bits Settings
UCSZn2
UCSZn1
UCSZn0
Character Size
5-bit
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
6-bit
7-bit
8-bit
Reserved
Reserved
Reserved
9-bit
• Bit 0 – UCPOLn: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous mode is used. The UCPOLn bit sets
the relationship between data output change and data input sample, and the synchronous clock (XCKn).
Table 19-8. UCPOLn Bit Settings
UCPOLn
Transmitted Data Changed (Output of TxDn Pin)
Rising XCKn edge
Received Data Sampled (Input on RxDn Pin)
Falling XCKn edge
0
1
Falling XCKn edge
Rising XCKn edge
19.11.5 UBRRnL and UBRRnH – USART Baud Rate Registers
Bit
15
14
13
12
11
10
9
8
–
–
–
–
UBRR[11:8]
UBRRnH
UBRRnL
UBRR[7:0]
7
R
6
R
5
R
4
R
3
R/W
R/W
0
2
R/W
R/W
0
1
R/W
R/W
0
0
R/W
R/W
0
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
0
0
0
0
0
0
0
0
• Bit 15:12 – Reserved
These bits are reserved for future use. For compatibility with future devices, these bit must be written to zero when UBRRH
is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRH contains the four most significant bits, and the
UBRRL contains the eight least significant bits of the USART baud rate. Ongoing transmissions by the transmitter and
receiver will be corrupted if the baud rate is changed. Writing UBRRL will trigger an immediate update of the baud rate
prescaler.
19.12 Examples of Baud Rate Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for asynchronous operation can be
generated by using the UBRR settings in Table 19-9 on page 167 to Table 19-12 on page 168. UBRR values which yield an
actual baud rate differing less than 0.5% from the target baud rate, are bold in the table. Higher error ratings are acceptable,
but the receiver will have less noise resistance when the error ratings are high, especially for large serial frames (see Section
19.9.3 “Asynchronous Operational Range” on page 161). The error values are calculated using the following equation:
BaudRateClosest Match
--------------------------------------------------
Error[%] =
– 1 • 100%
BaudRate
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Table 19-9. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies
fosc = 1.0000MHz
U2Xn = 0 U2Xn = 1
UBRR UBRR
fosc = 1.8432MHz
U2Xn = 0 U2Xn = 1
UBRR UBRR
fosc = 2.0000MHz
U2Xn = 0 U2Xn = 1
UBRR UBRR
Baud
Rate
(bps)
Error
0.2%
0.2%
–7.0%
8.5%
8.5%
8.5%
–18.6%
8.5%
–
Error
0.2%
0.2%
0.2%
–3.5%
–7.0%
8.5%
8.5%
8.5%
–18.6%
8.5%
–
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–25.0%
0.0%
–
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–
Error
0.2%
0.2%
0.2%
–3.5%
–7.0%
8.5%
8.5%
8.5%
–18.6%
8.5%
–
Error
0.2%
0.2%
0.2%
2.1%
0.2%
–3.5%
–7.0%
8.5%
8.5%
8.5%
–
2400
4800
25
12
6
51
25
12
8
47
23
11
7
95
47
23
15
11
7
51
25
12
8
103
51
25
16
12
8
9600
14.4k
19.2k
28.8k
38.4k
57.6k
76.8k
115.2k
230.4k
250k
3
2
6
5
6
1
3
3
3
1
2
2
5
2
6
0
1
1
3
1
3
–
1
1
2
1
2
–
–
0
0
1
0
1
–
–
–
–
0
–
–
–
–
–
–
–
–
–
–
–
0
0.0%
Max.(1)
62.5kbps
125kbps
115.2kbps
230.4kbps
125kbps
250kbps
Note:
1. UBRR = 0, error = 0.0%
Table 19-10. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 3.6864MHz
U2Xn = 0 U2Xn = 1
UBRR UBRR
fosc = 4.0000MHz
U2Xn = 0 U2Xn = 1
UBRR UBRR
fosc = 7.3728MHz
U2Xn = 0 U2Xn = 1
UBRR
Baud
Rate
(bps)
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–7.8%
–
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–7.8%
–7.8%
–
Error
0.2%
0.2%
0.2%
2.1%
0.2%
–3.5%
–7.0%
8.5%
8.5%
8.5%
8.5%
0.0%
–
Error
0.2%
0.2%
0.2%
–0.8%
0.2%
2.1%
0.2%
–3.5%
–7.0%
8.5%
8.5%
0.0%
0.0%
–
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–7.8%
–7.8%
–
UBRR
383
191
95
63
47
31
23
15
11
7
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–7.8%
–7.8%
–7.8%
2400
4800
9600
14.4k
19.2k
28.8k
38.4k
57.6k
76.8k
115.2k
230.4k
250k
95
47
23
15
11
7
191
95
47
31
23
15
11
7
103
51
25
16
12
8
207
103
51
34
25
16
12
8
191
95
47
31
23
15
11
7
5
6
3
3
2
5
2
6
5
1
3
1
3
3
0
1
0
1
1
3
0
1
0
1
1
3
0.5M
–
0
–
0
0
1
1M
–
–
–
–
–
–
–
0
Max.(1)
Note:
230.4kbps
460.8kbps
250kbps
0.5Mbps
460.8kbps
921.6kbps
1. UBRR = 0, error = 0.0%
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Table 19-11. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 8.0000MHz
U2Xn = 0 U2Xn = 1
UBRR UBRR
fosc = 11.0592MHz
U2Xn = 0 U2Xn = 1
UBRR UBRR
fosc = 14.7456MHz
U2Xn = 0 U2Xn = 1
UBRR UBRR
Baud
Rate
(bps)
Error
0.2%
0.2%
0.2%
–0.8%
0.2%
2.1%
0.2%
–3.5%
–7.0%
8.5%
8.5%
0.0%
0.0%
–
Error
–0.1%
0.2%
0.2%
0.6%
0.2%
–0.8%
0.2%
2.1%
0.2%
–3.5%
8.5%
0.0%
0.0%
0.0%
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–7.8%
–
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–7.8%
–7.8%
–
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
–7.8%
–7.8%
–7.8%
Error
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
5.3%
–7.8%
–7.8%
2400
4800
9600
14.4k
19.2k
28.8k
38.4k
57.6k
76.8k
115.2k
230.4k
250k
207
103
51
34
25
16
12
8
416
207
103
68
51
34
25
16
12
8
287
143
71
47
35
23
17
11
8
575
287
143
95
71
47
35
23
17
11
5
383
191
95
63
47
31
23
15
11
7
767
383
191
127
95
63
47
31
23
15
7
6
3
5
1
3
2
3
1
3
2
5
3
6
0.5M
0
1
–
2
1
3
1M
–
0
–
–
–
0
1
Max(1)
Note:
0.5Mbps
1Mbps
691.2kbps
1.3824Mbps
921.6kbps
1.8432Mbps
1. UBRR = 0, error = 0.0%
Table 19-12. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 16.0000MHz
U2Xn = 0
U2Xn = 1
Baud Rate (bps)
2400
UBRR
416
207
103
68
51
34
25
16
12
8
Error
–0.1%
0.2%
0.2%
0.6%
0.2%
–0.8%
0.2%
2.1%
0.2%
–3.5%
8.5%
0.0%
0.0%
0.0%
UBRR
832
416
207
138
103
68
Error
0.0%
–0.1%
0.2%
–0.1%
0.2%
0.6%
0.2%
–0.8%
0.2%
2.1%
–3.5%
0.0%
0.0%
0.0%
4800
9600
14.4k
19.2k
28.8k
38.4k
51
57.6k
34
76.8k
25
115.2k
230.4k
250k
16
3
8
3
7
0.5M
1
3
1M
0
1
Max.(1)
1Mbps
2Mbps
Note:
1. UBRR = 0, error = 0.0%
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20. USART in SPI Mode
20.1 Features
●
●
●
●
●
●
●
●
Full duplex, three-wire synchronous data transfer
Master operation
Supports all four SPI modes of operation (mode 0, 1, 2, and 3)
LSB first or MSB first data transfer (configurable data order)
Queued operation (double buffered)
High resolution baud rate generator
High speed operation (fXCKmax = fCK/2)
Flexible interrupt generation
20.2 Overview
The universal synchronous and asynchronous serial receiver and transmitter (USART) can be set to a master SPI compliant
mode of operation.
Setting both UMSELn1:0 bits to one enables the USART in MSPIM logic. In this mode of operation the SPI master control
logic takes direct control over the USART resources. These resources include the transmitter and receiver shift register and
buffers, and the baud rate generator. The parity generator and checker, the data and clock recovery logic, and the RX and
TX control logic is disabled. The USART RX and TX control logic is replaced by a common SPI transfer control logic.
However, the pin control logic and interrupt generation logic is identical in both modes of operation.
The I/O register locations are the same in both modes. However, some of the functionality of the control registers changes
when using MSPIM.
20.3 Clock Generation
The clock generation logic generates the base clock for the transmitter and receiver. For USART MSPIM mode of operation
only internal clock generation (i.e. master operation) is supported. The data direction register for the XCKn pin (DDR_XCKn)
must therefore be set to one (i.e. as output) for the USART in MSPIM to operate correctly. Preferably the DDR_XCKn should
be set up before the USART in MSPIM is enabled (i.e. TXENn and RXENn bit set to one).
The internal clock generation used in MSPIM mode is identical to the USART synchronous master mode. The baud rate or
UBRRn setting can therefore be calculated using the same equations, see Table 20-1:
Table 20-1. Equations for Calculating Baud Rate Register Setting
Operating Mode
Equation for Calculating Baud Rate(1)
Equation for Calculating UBRRn Value
f
f
OSC
OSC
-------------------
-------------------------------------
UBRRn =
– 1
Synchronous master mode
BAUD =
2BAUD
2(UBRRn + 1)
Note:
1. The baud rate is defined to be the transfer rate in bit per second (bps)
BAUD
Baud rate (in bits per second, bps)
fOSC
System oscillator clock frequency
UBRRn
Contents of the UBRRnH and UBRRnL registers, (0-4095
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20.4 SPI Data Modes and Timing
There are four combinations of XCKn (SCK) phase and polarity with respect to serial data, which are determined by control
bits UCPHAn and UCPOLn. The data transfer timing diagrams are shown in Figure 20-1. Data bits are shifted out and
latched in on opposite edges of the XCKn signal, ensuring sufficient time for data signals to stabilize. The UCPOLn and
UCPHAn functionality is summarized in Table 20-2. Note that changing the setting of any of these bits will corrupt all ongoing
communication for both the receiver and transmitter.
Table 20-2. UCPOLn and UCPHAn Functionality
UCPOLn
UCPHAn
SPI Mode
Leading Edge
Sample (rising)
Setup (rising)
Sample (falling)
Setup (falling)
Trailing Edge
Setup (falling)
Sample (falling)
Setup (rising)
Sample (rising)
0
0
1
1
0
1
0
1
0
1
2
3
Figure 20-1. UCPHAn and UCPOLn Data Transfer Timing Diagrams
UCPOL = 0
UCPOL = 1
XCK
XCK
Data setup (TXD)
Data setup (TXD)
Data sample (RXD)
Data sample (RXD)
XCK
Data setup (TXD)
Data sample (RXD)
XCK
Data setup (TXD)
Data sample (RXD)
20.5 Frame Formats
A serial frame for the MSPIM is defined to be one character of 8 data bits. The USART in MSPIM mode has two valid frame
formats:
●
●
8-bit data with MSB first
8-bit data with LSB first
A frame starts with the least or most significant data bit. Then the next data bits, up to a total of eight, are succeeding, ending
with the most or least significant bit accordingly. When a complete frame is transmitted, a new frame can directly follow it, or
the communication line can be set to an idle (high) state.
The UDORDn bit in UCSRnC sets the frame format used by the USART in MSPIM mode. The receiver and transmitter use
the same setting. Note that changing the setting of any of these bits will corrupt all ongoing communication for both the
receiver and transmitter.
16-bit data transfer can be achieved by writing two data bytes to UDRn. A UART transmit complete interrupt will then signal
that the 16-bit value has been shifted out.
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20.5.1 USART MSPIM Initialization
The USART in MSPIM mode has to be initialized before any communication can take place. The initialization process
normally consists of setting the baud rate, setting master mode of operation (by setting DDR_XCKn to one), setting frame
format and enabling the transmitter and the receiver. Only the transmitter can operate independently. For interrupt driven
USART operation, the global interrupt flag should be cleared (and thus interrupts globally disabled) when doing the
initialization.
Note:
To ensure immediate initialization of the XCKn output the baud-rate register (UBRRn) must be zero at the time
the transmitter is enabled. Contrary to the normal mode USART operation the UBRRn must then be written to
the desired value after the transmitter is enabled, but before the first transmission is started. Setting UBRRn to
zero before enabling the transmitter is not necessary if the initialization is done immediately after a reset since
UBRRn is reset to zero.
Before doing a re-initialization with changed baud rate, data mode, or frame format, be sure that there is no ongoing
transmissions during the period the registers are changed. The TXCn flag can be used to check that the transmitter has
completed all transfers, and the RXCn flag can be used to check that there are no unread data in the receive buffer. Note
that the TXCn flag must be cleared before each transmission (before UDRn is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C function that are equal in
functionality. The examples assume polling (no interrupts enabled). The baud rate is given as a function parameter. For the
assembly code, the baud rate parameter is assumed to be stored in the r17:r16 registers.
Assembly Code Example(1)
USART_Init:
clr r18
out UBRRnH,r18
out UBRRnL,r18
; Setting the XCKn port pin as output, enables master mode.
sbi XCKn_DDR, XCKn
; Set MSPI mode of operation and SPI data mode 0.
ldi r18, (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn)
out UCSRnC,r18
; Enable receiver and transmitter.
ldi r18, (1<<RXENn)|(1<<TXENn)
out UCSRnB,r18
; Set baud rate.
; IMPORTANT: The Baud Rate must be set after the transmitter is
enabled!
out UBRRnH, r17
out UBRRnL, r18
ret
C Code Example(1)
void USART_Init(unsigned int baud)
{
UBRRn = 0;
/* Setting the XCKn port pin as output, enables master mode. */
XCKn_DDR |= (1<<XCKn);
/* Set MSPI mode of operation and SPI data mode 0. */
UCSRnC = (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn);
/* Enable receiver and transmitter. */
UCSRnB = (1<<RXENn)|(1<<TXENn);
/* Set baud rate. */
/* IMPORTANT: The Baud Rate must be set after the transmitter is
enabled
*/
UBRRn = baud;
}
Note:
1. See Section 4. “About Code Examples” on page 8.
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20.6 Data Transfer
Using the USART in MSPI mode requires the transmitter to be enabled, i.e. the TXENn bit in the UCSRnB register is set to
one. When the transmitter is enabled, the normal port operation of the TxDn pin is overridden and given the function as the
transmitter's serial output. Enabling the receiver is optional and is done by setting the RXENn bit in the UCSRnB register to
one. When the receiver is enabled, the normal pin operation of the RxDn pin is overridden and given the function as the
receiver's serial input. The XCKn will in both cases be used as the transfer clock.
After initialization the USART is ready for doing data transfers. A data transfer is initiated by writing to the UDRn I/O location.
This is the case for both sending and receiving data since the transmitter controls the transfer clock. The data written to
UDRn is moved from the transmit buffer to the shift register when the shift register is ready to send a new frame.
Note:
To keep the input buffer in sync with the number of data bytes transmitted, the UDRn register must be read
once for each byte transmitted. The input buffer operation is identical to normal USART mode, i.e. if an
overflow occurs the character last received will be lost, not the first data in the buffer. This means that if four
bytes are transferred, byte 1 first, then byte 2, 3, and 4, and the UDRn is not read before all transfers are
completed, then byte 3 to be received will be lost, and not byte 1.
The following code examples show a simple USART in MSPIM mode transfer function based on polling of the data register
empty (UDREn) flag and the receive complete (RXCn) flag. The USART has to be initialized before the function can be used.
For the assembly code, the data to be sent is assumed to be stored in register R16 and the data received will be available in
the same register (R16) after the function returns.
The function simply waits for the transmit buffer to be empty by checking the UDREn flag, before loading it with new data to
be transmitted. The function then waits for data to be present in the receive buffer by checking the RXCn flag, before reading
the buffer and returning the value.
Assembly Code Example(1)
USART_MSPIM_Transfer:
; Wait for empty transmit buffer
sbis UCSRnA, UDREn
rjmp USART_MSPIM_Transfer
; Put data (r16) into buffer, sends the data
out UDRn,r16
; Wait for data to be received
USART_MSPIM_Wait_RXCn:
sbis UCSRnA, RXCn
rjmp USART_MSPIM_Wait_RXCn
; Get and return received data from buffer
in r16, UDRn
ret
C Code Example(1)
unsigned char USART_Receive(void)
{
/* Wait for empty transmit buffer */
while (!(UCSRnA & (1<<UDREn)));
/* Put data into buffer, sends the data */
UDRn = data;
/* Wait for data to be received */
while (!(UCSRnA & (1<<RXCn)));
/* Get and return received data from buffer */
return UDRn;
}
Note:
1. See Section 4. “About Code Examples” on page 8.
20.6.1 Transmitter and Receiver Flags and Interrupts
The RXCn, TXCn, and UDREn flags and corresponding interrupts in USART in MSPIM mode are identical in function to the
normal USART operation. However, the receiver error status flags (FE, DOR, and PE) are not in use and is always read as
zero.
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20.6.2 Disabling the Transmitter or Receiver
The disabling of the transmitter or receiver in USART in MSPIM mode is identical in function to the normal USART operation.
20.7 AVR USART MSPIM versus AVR SPI
The USART in MSPIM mode is fully compatible with the AVR® SPI regarding:
●
●
●
●
Master mode timing diagram.
The UCPOLn bit functionality is identical to the SPI CPOL bit.
The UCPHAn bit functionality is identical to the SPI CPHA bit.
The UDORDn bit functionality is identical to the SPI DORD bit.
However, since the USART in MSPIM mode reuses the USART resources, the use of the USART in MSPIM mode is
somewhat different compared to the SPI. In addition to differences of the control register bits, and that only master operation
is supported by the USART in MSPIM mode, the following features differ between the two modules:
●
●
●
●
The USART in MSPIM mode includes (double) buffering of the transmitter. The SPI has no buffer.
The USART in MSPIM mode receiver includes an additional buffer level.
The SPI WCOL (write collision) bit is not included in USART in MSPIM mode.
The SPI double speed mode (SPI2X) bit is not included. However, the same effect is achieved by setting UBRRn
accordingly.
●
●
Interrupt timing is not compatible.
Pin control differs due to the master only operation of the USART in MSPIM mode.
A comparison of the USART in MSPIM mode and the SPI pins is shown in Table 20-3.
Table 20-3. Comparison of USART in MSPIM mode and SPI pins.
USART_MSPIM
TxDn
SPI
MOSI
MISO
SCK
SS
Comment
Master out only
RxDn
Master in only
XCKn
(Functionally identical)
Not supported by USART in MSPIM
(N/A)
20.8 Register Description
The following section describes the registers used for SPI operation using the USART.
20.8.1 UDRn – USART MSPIM I/O Data Register
The function and bit description of the USART data register (UDRn) in MSPI mode is identical to normal USART operation.
See Section 19.11.1 “UDRn – USART I/O Data Register n” on page 163.
20.8.2 UCSRnA – USART MSPIM Control and Status Register n A
Bit
7
RXCn
R/W
0
6
TXCn
R/W
0
5
UDREn
R/W
0
4
–
3
–
2
–
1
–
0
–
UCSRnA
Read/Write
Initial Value
R
0
R
0
R
1
R
1
R
0
• Bit 7 – RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive buffer is empty (i.e., does
not contain any unread data). If the receiver is disabled, the receive buffer will be flushed and consequently the RXCn bit will
become zero. The RXCn flag can be used to generate a receive complete interrupt (see description of the RXCIEn bit).
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• Bit 6 – TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the transmit shift register has been shifted out and there are no new data currently
present in the transmit buffer (UDRn). The TXCn flag bit is automatically cleared when a transmit complete interrupt is
executed, or it can be cleared by writing a one to its bit location. The TXCn flag can generate a transmit complete interrupt
(see description of the TXCIEn bit).
• Bit 5 – UDREn: USART Data Register Empty
The UDREn flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREn is one, the buffer is empty,
and therefore ready to be written. The UDREn flag can generate a data register empty interrupt (see description of the
UDRIE bit). UDREn is set after a reset to indicate that the transmitter is ready.
• Bit 4:0 – Reserved in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices, these bits must be written
to zero when UCSRnA is written.
20.8.3 UCSRnB – USART MSPIM Control and Status Register n B
Bit
7
RXCIEn
R/W
0
6
TXCIEn
R/W
0
5
UDRIE
R/W
0
4
RXENn
R/W
0
3
TXENn
R/W
0
2
–
1
–
0
–
UCSRnB
Read/Write
Initial Value
R
1
R
1
R
0
• Bit 7 – RXCIEn: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXCn flag. A USART receive complete interrupt will be generated only if the
RXCIEn bit is written to one, the global interrupt flag in SREG is written to one and the RXCn bit in UCSRnA is set.
• Bit 6 – TXCIEn: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXCn flag. A USART transmit complete interrupt will be generated only if the
TXCIEn bit is written to one, the global interrupt flag in SREG is written to one and the TXCn bit in UCSRnA is set.
• Bit 5 – UDRIE: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDREn flag. A data register empty interrupt will be generated only if the
UDRIE bit is written to one, the global interrupt flag in SREG is written to one and the UDREn bit in UCSRnA is set.
• Bit 4 – RXENn: Receiver Enable
Writing this bit to one enables the USART receiver in MSPIM mode. The receiver will override normal port operation for the
RxDn pin when enabled. Disabling the receiver will flush the receive buffer. Only enabling the receiver in MSPI mode
(i.e. setting RXENn=1 and TXENn=0) has no meaning since it is the transmitter that controls the transfer clock and since
only master mode is supported.
• Bit 3 – TXENn: Transmitter Enable
Writing this bit to one enables the USART transmitter. The transmitter will override normal port operation for the TxDn pin
when enabled. The disabling of the transmitter (writing TXENn to zero) will not become effective until ongoing and pending
transmissions are completed, i.e., when the transmit shift register and transmit buffer register do not contain data to be
transmitted. When disabled, the transmitter will no longer override the TxDn port.
• Bit 2:0 – Reserved in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices, these bits must be written
to zero when UCSRnB is written.
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20.8.4 UCSRnC – USART MSPIM Control and Status Register n C
Bit
7
6
5
–
4
–
3
–
2
1
0
UMSELn1 UMSELn0
UDORDn UCPHAn UCPOLn UCSRnC
Read/Write
Initial Value
R/W
0
R/W
0
R
0
R
0
R
0
R/W
1
R/W
1
R/W
0
• Bit 7:6 – UMSELn1:0: USART Mode Select
These bits select the mode of operation of the USART as shown in Table 20-4. See Section 19.11.4 “UCSRnC – USART
Control and Status Register n C” on page 165 for full description of the normal USART operation. The MSPIM is enabled
when both UMSELn bits are set to one. The UDORDn, UCPHAn, and UCPOLn can be set in the same write operation where
the MSPIM is enabled.
Table 20-4. UMSELn Bits Settings
UMSELn1
UMSELn0
Mode
0
0
1
1
0
1
0
1
Asynchronous USART
Synchronous USART
(Reserved)
Master SPI (MSPIM)
• Bit 5:3 – Reserved in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices, these bits must be written
to zero when UCSRnC is written.
• Bit 2 – UDORDn: Data Order
When set to one the LSB of the data word is transmitted first. When set to zero the MSB of the data word is transmitted first.
Refer to the frame formats section page 4 for details.
• Bit 1 – UCPHAn: Clock Phase
The UCPHAn bit setting determine if data is sampled on the leasing edge (first) or tailing (last) edge of XCKn. Refer to the
SPI data modes and timing section page 4 for details.
• Bit 0 – UCPOLn: Clock Polarity
The UCPOLn bit sets the polarity of the XCKn clock. The combination of the UCPOLn and UCPHAn bit settings determine
the timing of the data transfer. Refer to the SPI data modes and Timing section page 4 for details.
20.8.5 UBRRnL and UBRRnH –USART MSPIM Baud Rate Registers
The function and bit description of the baud rate registers in MSPI mode is identical to normal USART operation. See
Section 19.11.5 “UBRRnL and UBRRnH – USART Baud Rate Registers” on page 166.
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21. Two-wire Serial Interface
21.1 Features
●
●
●
●
●
●
●
●
●
●
Simple yet powerful and flexible communication interface, only two bus lines needed
Both master and slave operation supported
Device can operate as transmitter or receiver
7-bit address space allows up to 128 different slave addresses
Multi-master arbitration support
Up to 400kHz data transfer speed
Slew-rate limited output drivers
Noise suppression circuitry rejects spikes on bus lines
Fully programmable slave address with general call support
Address recognition causes wake-up when AVR® is in sleep mode
21.2 Two-wire Serial Interface Bus Definition
The two-wire serial interface (TWI) is ideally suited for typical microcontroller applications. The TWI protocol allows the
systems designer to interconnect up to 128 different devices using only two bi-directional bus lines, one for clock (SCL) and
one for data (SDA). The only external hardware needed to implement the bus is a single pull-up resistor for each of the TWI
bus lines. All devices connected to the bus have individual addresses, and mechanisms for resolving bus contention are
inherent in the TWI protocol.
Figure 21-1. TWI Bus Interconnection
V
CC
Device 1
Device 2
Device 3 ........ Device n
R1
R2
SDA
SCL
21.2.1 TWI Terminology
The following definitions are frequently encountered in this section.
Table 21-1. TWI Terminology
Term
Master
Description
The device that initiates and terminates a transmission. The master also generates the SCL clock
The device addressed by a master
Slave
Transmitter
Receiver
The device placing data on the bus
The device reading data from the bus
The power reduction TWI bit, PRTWI bit in Section 10.12.3 “PRR0 – Power Reduction Register 0” on page 39 must be
written to zero to enable the 2-wire serial interface.
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21.2.2 Electrical Interconnection
As depicted in Figure 21-1 on page 176, both bus lines are connected to the positive supply voltage through pull-up
resistors. The bus drivers of all TWI-compliant devices are open-drain or open-collector. This implements a wired-AND
function which is essential to the operation of the interface. A low level on a TWI bus line is generated when one or more TWI
devices output a zero. A high level is output when all TWI devices trim-state their outputs, allowing the pull-up resistors to
pull the line high. Note that all AVR® devices connected to the TWI bus must be powered in order to allow any bus operation.
The number of devices that can be connected to the bus is only limited by the bus capacitance limit of 400pF and the 7-bit
slave address space. A detailed specification of the electrical characteristics of the TWI is given in Section 28.7 “SPI Timing
Characteristics” on page 292. Two different sets of specifications are presented there, one relevant for bus speeds below
100kHz, and one valid for bus speeds up to 400kHz.
21.3 Data Transfer and Frame Format
21.3.1 Transferring Bits
Each data bit transferred on the TWI bus is accompanied by a pulse on the clock line. The level of the data line must be
stable when the clock line is high. The only exception to this rule is for generating start and stop conditions.
Figure 21-2. Data Validity
SDA
SCL
Data Stable
Data Change
Data Stable
21.3.2 START and STOP Conditions
The master initiates and terminates a data transmission. The transmission is initiated when the master issues a START
condition on the bus, and it is terminated when the master issues a STOP condition. Between a START and a STOP
condition, the bus is considered busy, and no other master should try to seize control of the bus. A special case occurs when
a new START condition is issued between a START and STOP condition. This is referred to as a REPEATED START
condition, and is used when the master wishes to initiate a new transfer without relinquishing control of the bus. After a
REPEATED START, the bus is considered busy until the next STOP. This is identical to the START behavior, and therefore
START is used to describe both START and REPEATED START for the remainder of this datasheet, unless otherwise
noted. As depicted below, START and STOP conditions are signalled by changing the level of the SDA line when the SCL
line is high.
Figure 21-3. START, REPEATED START and STOP conditions
SDA
SCL
START
STOP START
REPEATED START
STOP
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21.3.3 Address Packet Format
All address packets transmitted on the TWI bus are 9 bits long, consisting of 7 address bits, one READ/WRITE control bit
and an acknowledge bit. If the READ/WRITE bit is set, a read operation is to be performed, otherwise a write operation
should be performed. When a slave recognizes that it is being addressed, it should acknowledge by pulling SDA low in the
ninth SCL (ACK) cycle. If the addressed Slave is busy, or for some other reason can not service the master’s request, the
SDA line should be left high in the ACK clock cycle. The master can then transmit a STOP condition, or a REPEATED
START condition to initiate a new transmission. An address packet consisting of a slave address and a READ or a WRITE
bit is called SLA+R or SLA+W, respectively.
The MSB of the address byte is transmitted first. Slave addresses can freely be allocated by the designer, but the address
0000 000 is reserved for a general call.
When a general call is issued, all slaves should respond by pulling the SDA line low in the ACK cycle. A general call is used
when a master wishes to transmit the same message to several slaves in the system. When the general call address
followed by a Write bit is transmitted on the bus, all slaves set up to acknowledge the general call will pull the SDA line low in
the ack cycle. The following data packets will then be received by all the slaves that acknowledged the general call. Note that
transmitting the general call address followed by a read bit is meaningless, as this would cause contention if several slaves
started transmitting different data.
All addresses of the format 1111 xxx should be reserved for future purposes.
Figure 21-4. Address Packet Format
Addr MSB
Addr LSB
R/W
ACK
SDA
SCL
1
2
7
8
9
START
21.3.4 Data Packet Format
All data packets transmitted on the TWI bus are nine bits long, consisting of one data byte and an acknowledge bit. During a
data transfer, the master generates the clock and the START and STOP conditions, while the receiver is responsible for
acknowledging the reception. An acknowledge (ACK) is signalled by the receiver pulling the SDA line low during the ninth
SCL cycle. If the receiver leaves the SDA line high, a NACK is signalled. When the receiver has received the last byte, or for
some reason cannot receive any more bytes, it should inform the transmitter by sending a NACK after the final byte. The
MSB of the data byte is transmitted first.
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Figure 21-5. Data Packet Format
Data MSB
Data LSB
ACK
Aggregate
SDA
SDA from
Transmitter
SDA from
Receiver
SCL from
Master
1
2
7
8
9
STOP, REPEATED
START or next
Data Byte
SLA + R/W
Data Byte
21.3.5 Combining Address and Data Packets into a Transmission
A transmission basically consists of a START condition, a SLA+R/W, one or more data packets and a STOP condition. An
empty message, consisting of a START followed by a STOP condition, is illegal. Note that the Wired-ANDing of the SCL line
can be used to implement handshaking between the master and the slave. The slave can extend the SCL low period by
pulling the SCL line low. This is useful if the clock speed set up by the master is too fast for the slave, or the slave needs
extra time for processing between the data transmissions. The slave extending the SCL low period will not affect the SCL
high period, which is determined by the master. As a consequence, the slave can reduce the TWI data transfer speed by
prolonging the SCL duty cycle.
Figure 21-6 shows a typical data transmission. Note that several data bytes can be transmitted between the SLA+R/W and
the STOP condition, depending on the software protocol implemented by the application software.
Figure 21-6. Typical Data Transmission
Addr MSB
Addr LSB R/W
ACK
Data MSB
Data LSB ACK
SDA
SCL
1
2
7
8
9
1
2
7
8
9
START
SLA + R/W
Data Byte
STOP
21.4 Multi-master Bus Systems, Arbitration and Synchronization
The TWI protocol allows bus systems with several masters. Special concerns have been taken in order to ensure that
transmissions will proceed as normal, even if two or more masters initiate a transmission at the same time. Two problems
arise in multi-master systems:
●
An algorithm must be implemented allowing only one of the masters to complete the transmission. All other masters
should cease transmission when they discover that they have lost the selection process. This selection process is
called arbitration. When a contending master discovers that it has lost the arbitration process, it should immediately
switch to slave mode to check whether it is being addressed by the winning master. The fact that multiple masters
have started transmission at the same time should not be detectable to the slaves, i.e. the data being transferred on
the bus must not be corrupted.
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●
Different masters may use different SCL frequencies. A scheme must be devised to synchronize the serial clocks
from all masters, in order to let the transmission proceed in a lockstep fashion. This will facilitate the arbitration
process.
The wired-ANDing of the bus lines is used to solve both these problems. The serial clocks from all masters will be wired-
ANDed, yielding a combined clock with a high period equal to the one from the master with the shortest high period. The low
period of the combined clock is equal to the low period of the master with the longest low period. Note that all masters listen
to the SCL line, effectively starting to count their SCL high and low time-out periods when the combined SCL line goes high
or low, respectively.
Figure 21-7. SCL Synchronization Between Multiple Masters
TAlow
TAhigh
SCL from
Master A
SCL from
Master B
SCL Bus
Line
TBlow
TBhigh
Masters Start
Counting Low Period
Masters Start
Counting High Period
Arbitration is carried out by all masters continuously monitoring the SDA line after outputting data. If the value read from the
SDA line does not match the value the master had output, it has lost the arbitration. Note that a master can only lose
arbitration when it outputs a high SDA value while another master outputs a low value. The losing master should
immediately go to slave mode, checking if it is being addressed by the winning master. The SDA line should be left high, but
losing masters are allowed to generate a clock signal until the end of the current data or address packet. Arbitration will
continue until only one master remains, and this may take many bits. If several masters are trying to address the same slave,
arbitration will continue into the data packet.
Figure 21-8. Arbitration Between Two Masters
Master A Loses
START
Arbitration, SDA ≠ SDA
A
SDA from
Master A
SDA from
Master B
SDA Line
Synchronized
SCL Line
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Note that arbitration is not allowed between:
●
●
●
A REPEATED START condition and a data bit.
A STOP condition and a data bit.
A REPEATED START and a STOP condition.
It is the user software’s responsibility to ensure that these illegal arbitration conditions never occur. This implies that in
multi-master systems, all data transfers must use the same composition of SLA+R/W and data packets. In other words: All
transmissions must contain the same number of data packets, otherwise the result of the arbitration is undefined.
21.5 Overview of the TWI Module
The TWI module is comprised of several submodules, as shown in Figure 21-9. All registers drawn in a thick line are
accessible through the AVR® data bus.
Figure 21-9. Overview of the TWI Module
SCL
SDA
Slew-rate
Control
Spike
Filter
Slew-rate
Control
Spike
Filter
Bus Interface Unit
Bit Rate Generator
START/ STOP
Spike Suppression
Prescaler
Control
Address/ Data Shift
Register (TWDR)
Bit Rate Register
(TWBR)
Arbitration detection
Ack
Address Match Unit
Control Unit
Address Register
(TWAR)
Status Register
(TWSR)
Control Register
(TWCR)
State Machine and
Status control
Address Comparator
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21.5.1 SCL and SDA Pins
These pins interface the AVR® TWI with the rest of the MCU system. The output drivers contain a slew-rate limiter in order to
conform to the TWI specification. The input stages contain a spike suppression unit removing spikes shorter than 50ns. Note
that the internal pull-ups in the AVR pads can be enabled by setting the PORT bits corresponding to the SCL and SDA pins,
as explained in the I/O port section. The internal pull-ups can in some systems eliminate the need for external ones.
21.5.2 Bit Rate Generator Unit
This unit controls the period of SCL when operating in a master mode. The SCL period is controlled by settings in the TWI Bit
rate register (TWBR) and the prescaler bits in the TWI status register (TWSR). Slave operation does not depend on bit rate
or prescaler settings, but the CPU clock frequency in the slave must be at least 16 times higher than the SCL frequency.
Note that slaves may prolong the SCL low period, thereby reducing the average TWI bus clock period. The SCL frequency is
generated according to the following equation:
CPU Clock frequency
---------------------------------------------------------
TWPS
SCL frequency =
16 + 2(TWBR) 4
●
●
TWBR = value of the TWI bit rate register.
TWPS = value of the prescaler bits in the TWI status register.
Note:
Pull-up resistor values should be selected according to the SCL frequency and the capacitive bus line load.
See 2-wire serial bus requirements in Table 28-9 on page 293 for value of pull-up resistor.
21.5.3 Bus Interface Unit
This unit contains the data and address shift register (TWDR), a START/STOP controller and arbitration detection hardware.
The TWDR contains the address or data bytes to be transmitted, or the address or data bytes received. In addition to the
8-bit TWDR, the bus interface unit also contains a register containing the (N)ACK bit to be transmitted or received. This
(N)ACK register is not directly accessible by the application software. However, when receiving, it can be set or cleared by
manipulating the TWI control register (TWCR). When in transmitter mode, the value of the received (N)ACK bit can be
determined by the value in the TWSR.
The START/STOP controller is responsible for generation and detection of START, REPEATED START, and STOP
conditions. The START/STOP controller is able to detect START and STOP conditions even when the AVR MCU is in one of
the sleep modes, enabling the MCU to wake up if addressed by a master.
If the TWI has initiated a transmission as master, the arbitration detection hardware continuously monitors the transmission
trying to determine if arbitration is in process. If the TWI has lost an arbitration, the control unit is informed. correct action can
then be taken and appropriate status codes generated.
21.5.4 Address Match Unit
The address match unit checks if received address bytes match the seven-bit address in the TWI address register (TWAR).
If the TWI general call recognition enable (TWGCE) bit in the TWAR is written to one, all incoming address bits will also be
compared against the general call address. Upon an address match, the control unit is informed, allowing correct action to
be taken. The TWI may or may not acknowledge its address, depending on settings in the TWCR. The address match unit is
able to compare addresses even when the AVR MCU is in sleep mode, enabling the MCU to wake up if addressed by a
master.
21.5.5 Control Unit
The control unit monitors the TWI bus and generates responses corresponding to settings in the TWI control register
(TWCR). When an event requiring the attention of the application occurs on the TWI bus, the TWI interrupt flag (TWINT) is
asserted. In the next clock cycle, the TWI status register (TWSR) is updated with a status code identifying the event. The
TWSR only contains relevant status information when the TWI interrupt flag is asserted. At all other times, the TWSR
contains a special status code indicating that no relevant status information is available. As long as the TWINT flag is set, the
SCL line is held low. This allows the application software to complete its tasks before allowing the TWI transmission to
continue.
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The TWINT flag is set in the following situations:
●
●
●
●
●
●
●
●
After the TWI has transmitted a START/REPEATED START condition.
After the TWI has transmitted SLA+R/W.
After the TWI has transmitted an address byte.
After the TWI has lost arbitration.
After the TWI has been addressed by own slave address or general call.
After the TWI has received a data byte.
After a STOP or REPEATED START has been received while still addressed as a slave.
When a bus error has occurred due to an illegal START or STOP condition.
21.6 Using the TWI
The AVR® TWI is byte-oriented and interrupt based. Interrupts are issued after all bus events, like reception of a byte or
transmission of a START condition. Because the TWI is interrupt-based, the application software is free to carry on other
operations during a TWI byte transfer. Note that the TWI interrupt enable (TWIE) bit in TWCR together with the global
interrupt enable bit in SREG allow the application to decide whether or not assertion of the TWINT flag should generate an
interrupt request. If the TWIE bit is cleared, the application must poll the TWINT flag in order to detect actions on the TWI
bus.
When the TWINT flag is asserted, the TWI has finished an operation and awaits application response. In this case, the TWI
status register (TWSR) contains a value indicating the current state of the TWI bus. The application software can then
decide how the TWI should behave in the next TWI bus cycle by manipulating the TWCR and TWDR registers.
Figure 21-10 is a simple example of how the application can interface to the TWI hardware. In this example, a master wishes
to transmit a single data byte to a slave. This description is quite abstract, a more detailed explanation follows later in this
section. A simple code example implementing the desired behavior is also presented.
Figure 21-10. Interfacing the Application to the TWI in a Typical Transmission
3. Check TWSR to see if START was
sent. Application loads SLA + W into
TWDR, and loads appropriate control
signals into TWCR, makin sure that
TWINT is written to one,
5. Check TWSR to see if SLA + W was
sent and ACK received.
Application loads data intoTWDR, and
loads appropriate control signals into
TWCR, makin sure that TWINT is
written to one
7. Check TWSR to see if data was sent
and ACK received.
Application loads appropriate control
signals to send STOP into TWCR,
makin sure that TWINT is
written to one
1. Application
writes to TWCR to
initiate
transmission of
START
and TWSTA is written to zero.
TWI bus
START
SLA + W
A
Data
A
STOP
Indicates
TWINT set
4. TWINT set.
Status code indicates
SLA + W sent,
2. TWINT set.
Status code indicates
START condition sent
6. TWINT set.
Status code indicates
data sent, ACK received
ACK received
1. The first step in a TWI transmission is to transmit a START condition. This is done by writing a specific value into
TWCR, instructing the TWI hardware to transmit a START condition. Which value to write is described later on.
However, it is important that the TWINT bit is set in the value written. Writing a one to TWINT clears the flag. The
TWI will not start any operation as long as the TWINT bit in TWCR is set. Immediately after the application has
cleared TWINT, the TWI will initiate transmission of the START condition.
2. When the START condition has been transmitted, the TWINT flag in TWCR is set, and TWSR is updated with a
status code indicating that the START condition has successfully been sent.
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3. The application software should now examine the value of TWSR, to make sure that the START condition was
successfully transmitted. If TWSR indicates otherwise, the application software might take some special action,
like calling an error routine. Assuming that the status code is as expected, the application must load SLA+W into
TWDR. Remember that TWDR is used both for address and data. After TWDR has been loaded with the desired
SLA+W, a specific value must be written to TWCR, instructing the TWI hardware to transmit the SLA+W present in
TWDR. Which value to write is described later on. However, it is important that the TWINT bit is set in the value
written. Writing a one to TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit in
TWCR is set. Immediately after the application has cleared TWINT, the TWI will initiate transmission of the
address packet.
4. When the address packet has been transmitted, the TWINT flag in TWCR is set, and TWSR is updated with a
status code indicating that the address packet has successfully been sent. The status code will also reflect
whether a slave acknowledged the packet or not.
5. The application software should now examine the value of TWSR, to make sure that the address packet was
successfully transmitted, and that the value of the ACK bit was as expected. If TWSR indicates otherwise, the
application software might take some special action, like calling an error routine. Assuming that the status code is
as expected, the application must load a data packet into TWDR. Subsequently, a specific value must be written to
TWCR, instructing the TWI hardware to transmit the data packet present in TWDR. Which value to write is
described later on. However, it is important that the TWINT bit is set in the value written. Writing a one to TWINT
clears the flag. The TWI will not start any operation as long as the TWINT bit in TWCR is set. Immediately after the
application has cleared TWINT, the TWI will initiate transmission of the data packet.
6. When the data packet has been transmitted, the TWINT flag in TWCR is set, and TWSR is updated with a status
code indicating that the data packet has successfully been sent. The status code will also reflect whether a slave
acknowledged the packet or not.
7. The application software should now examine the value of TWSR, to make sure that the data packet was
successfully transmitted, and that the value of the ACK bit was as expected. If TWSR indicates otherwise, the
application software might take some special action, like calling an error routine. Assuming that the status code is
as expected, the application must write a specific value to TWCR, instructing the TWI hardware to transmit a
STOP condition. Which value to write is described later on. However, it is important that the TWINT bit is set in the
value written. Writing a one to TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit
in TWCR is set. Immediately after the application has cleared TWINT, the TWI will initiate transmission of the
STOP condition. Note that TWINT is NOT set after a STOP condition has been sent.
Even though this example is simple, it shows the principles involved in all TWI transmissions. These can be summarized as
follows:
●
●
●
When the TWI has finished an operation and expects application response, the TWINT flag is set. The SCL line is
pulled low until TWINT is cleared.
When the TWINT flag is set, the user must update all TWI registers with the value relevant for the next TWI bus cycle.
As an example, TWDR must be loaded with the value to be transmitted in the next bus cycle.
After all TWI register updates and other pending application software tasks have been completed, TWCR is written.
When writing TWCR, the TWINT bit should be set. Writing a one to TWINT clears the flag. The TWI will then
commence executing whatever operation was specified by the TWCR setting.
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In the following an assembly and C implementation of the example is given. Note that the code below assumes that several
definitions have been made, for example by using include-files.
Table 21-2. Assembly Code Example
Assembly Code Example
C Example
Comments
ldi
r16, (1<<TWINT)|(1<<TWSTA)|
(1<<TWEN)
TWCR, r16
TWCR = (1<<TWINT)|(1<<TWSTA)|
(1<<TWEN)
1
2
Send START condition
out
wait1:
in
sbrs
rjmp
while (!(TWCR & (1<<TWINT)))
Wait for TWINT flag set. This
indicates that the START
condition has been transmitted
r16,TWCR
r16,TWINT
wait1
;
in
andi
cpi
r16,TWSR
r16,0xF8
r16,START
ERROR
if ((TWSR & 0xF8)!= START)
Check value of TWI status
register. Mask prescaler bits. If
status different from START go
to ERROR
ERROR();
brne
3
4
5
ldi
out
ldi
r16,SLA_W
TWDR,r16
r16, (1<<TWINT) | (1<<TWEN)
TWCR, r16
TWDR = SLA_W;
TWCR = (1<<TWINT) | (1<<TWEN);
Load SLA_W into TWDR
register. Clear TWINT bit in
TWCR to start transmission of
address
out
wait2:
in
sbrs
rjmp
while (!(TWCR & (1<<TWINT)))
Wait for TWINT flag set. This
indicates that the SLA+W has
been transmitted, and
r16,TWCR
r16,TWINT
wait2
;
ACK/NACK has been received.
in
andi
cpi
r16,TWSR
r16,0xF8
r16, MT_SLA_ACK
ERROR
if ((TWSR & 0xF8)!= MT_SLA_ACK)
Check value of TWI status
register. Mask prescaler bits. If
status different from
ERROR();
brne
MT_SLA_ACK go to ERROR
ldi
out
ldi
r16, DATA
TWDR,r16
r16, (1<<TWINT) | (1<<TWEN)
TWCR, r16
TWDR = DATA;
TWCR = (1<<TWINT) | (1<<TWEN);
Load DATA into TWDR register.
Clear TWINT bit in TWCR to
start transmission of data
out
wait3:
in
sbrs
rjmp
while (!(TWCR & (1<<TWINT)))
Wait for TWINT flag set. This
indicates that the DATA has
been transmitted, and
r16,TWCR
r16,TWINT
wait3
;
6
7
ACK/NACK has been received.
in
andi
cpi
r16,TWSR
r16,0xF8
r16, MT_DATA_ACK
ERROR
if ((TWSR & 0xF8)!= MT_DATA_ACK) Check value of TWI status
ERROR();
register. Mask prescaler bits. If
status different from
MT_DATA_ACK go to ERROR
brne
ldi
r16, (1<<TWINT)|(1<<TWEN)|
(1<<TWSTO)
TWCR = (1<<TWINT)|(1<<TWEN)|
(1<<TWSTO);
Transmit STOP condition
out
TWCR, r16
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21.7 Transmission Modes
The TWI can operate in one of four major modes. These are named master transmitter (MT), master receiver (MR), slave
transmitter (ST) and slave receiver (SR). Several of these modes can be used in the same application. As an example, the
TWI can use MT mode to write data into a TWI EEPROM, MR mode to read the data back from the EEPROM. If other
masters are present in the system, some of these might transmit data to the TWI, and then SR mode would be used. It is the
application software that decides which modes are legal.
The following sections describe each of these modes. Possible status codes are described along with figures detailing data
transmission in each of the modes. These figures contain the following abbreviations:
S: START condition
Rs: REPEATED START condition
R: Read bit (high level at SDA)
W: Write bit (low level at SDA)
A: Acknowledge bit (low level at SDA)
A: Not acknowledge bit (high level at SDA)
Data: 8-bit data byte
P: STOP condition
SLA: Slave address
In Figure 21-12 on page 189 to Figure 21-18 on page 198, circles are used to indicate that the TWINT flag is set. The
numbers in the circles show the status code held in TWSR, with the prescaler bits masked to zero. At these points, actions
must be taken by the application to continue or complete the TWI transfer. The TWI transfer is suspended until the TWINT
flag is cleared by software.
When the TWINT flag is set, the status code in TWSR is used to determine the appropriate software action. For each status
code, the required software action and details of the following serial transfer are given in Table 21-3 on page 188 to
Table 21-6 on page 197. Note that the prescaler bits are masked to zero in these tables.
21.7.1 Master Transmitter Mode
In the master transmitter mode, a number of data bytes are transmitted to a slave receiver (see Figure 21-11). In order to
enter a master mode, a START condition must be transmitted. The format of the following address packet determines
whether master transmitter or master receiver mode is to be entered. If SLA+W is transmitted, MT mode is entered, if SLA+R
is transmitted, MR mode is entered. All the status codes mentioned in this section assume that the prescaler bits are zero or
are masked to zero.
Figure 21-11. Data Transfer in Master Transmitter Mode
V
CC
Device 1
Master
Transmitter
Device 2
Slave
Receiver
Device 3 ........ Device n
R1
R2
SDA
SCL
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A START condition is sent by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
1
0
X
1
0
X
TWEN must be set to enable the 2-wire serial interface, TWSTA must be written to one to transmit a START condition and
TWINT must be written to one to clear the TWINT flag. The TWI will then test the 2-wire serial bus and generate a START
condition as soon as the bus becomes free. After a START condition has been transmitted, the TWINT flag is set by
hardware, and the status code in TWSR will be 0x08 (see Table 21-3). In order to enter MT mode, SLA+W must be
transmitted. This is done by writing SLA+W to TWDR. Thereafter the TWINT bit should be cleared (by writing it to one) to
continue the transfer. This is accomplished by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
0
0
X
1
0
X
When SLA+W have been transmitted and an acknowledgement bit has been received, TWINT is set again and a number of
status codes in TWSR are possible. Possible status codes in master mode are 0x18, 0x20, or 0x38. The appropriate action
to be taken for each of these status codes is detailed in Table 21-3.
When SLA+W has been successfully transmitted, a data packet should be transmitted. This is done by writing the data byte
to TWDR. TWDR must only be written when TWINT is high. If not, the access will be discarded, and the write collision bit
(TWWC) will be set in the TWCR register. After updating TWDR, the TWINT bit should be cleared (by writing it to one) to
continue the transfer. This is accomplished by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
0
0
X
1
0
X
This scheme is repeated until the last byte has been sent and the transfer is ended by generating a STOP condition or a
repeated START condition. A STOP condition is generated by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
0
1
X
1
0
X
A REPEATED START condition is generated by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
1
0
X
1
0
X
After a repeated START condition (state 0x10) the 2-wire serial interface can access the same slave again, or a new slave
without transmitting a STOP condition. Repeated START enables the master to switch between slaves, master transmitter
mode and master receiver mode without losing control of the bus.
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Table 21-3. Status codes for Master Transmitter Mode
Application Software Response
Status Code
(TWSR)
Prescaler
Bits are 0
Status of the 2-wire
Serial Bus and 2-wire
Serial Interface
Hardware
To/from TWDR
To TWCR
STA STO TWINT TWEA
Next Action Taken by TWI Hardware
0x08
A START condition has
been transmitted
Load SLA+W
0
0
1
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
0x10
A repeated START
condition has been
transmitted
Load SLA+W or
Load SLA+R
0
0
0
0
1
1
X
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
SLA+R will be transmitted;
logic will switch to master receiver mode
0x18
0x20
0x28
0x30
0x38
SLA+W has been
transmitted; ACK has
been received
Load data byte or
0
0
1
X
Data byte will be transmitted and ACK or
NOT ACK will be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
SLA+W has been
transmitted; NOT ACK has
been received
Load data byte or
0
0
1
X
Data byte will be transmitted and ACK or
NOT ACK will be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
Data byte has been
transmitted; ACK has
been received
Load data byte or
0
0
1
X
Data byte will be transmitted and ACK or
NOT ACK will be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
Data byte has been
transmitted; NOT ACK has
been received
Load data byte or
0
0
1
X
Data byte will be transmitted and ACK or
NOT ACK will be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
Arbitration lost in SLA+W No TWDR action or
or data bytes
0
1
0
0
1
1
X
X
2-wire serial bus will be released and not
addressed slave mode entered
A START condition will be transmitted
when the bus becomes free
No TWDR action
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Figure 21-12. Formats and States in the Master Transmitter Mode
MT
Successfull
S
SLA
W
A
DATA
A
P
transmission
to a slave
receiver
$08
$18
$28
Next transfer
started with a
repeated start
condition
RS
SLA
W
$10
Not acknowledge
received after the
slave address
A
P
R
$20
MR
Not acknowledge
received after a
data byte
A
P
$30
Arbitration lost in slave
address or data byte
Other master
continues
Other master
continues
A or A
A or A
$38
A
$38
Arbitration lost and
addressed as slave
Other master
continues
To corresponding
states in slave mode
$68
$78
$B0
Any number of data bytes
From master to slave
From slave to master
DATA
A
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the Two-Wire Serial Bus.
The prescaler bits are zero or masked to zero
n
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21.7.2 Master Receiver Mode
In the master receiver mode, a number of data bytes are received from a slave transmitter (slave see Figure 21-13). In order
to enter a master mode, a START condition must be transmitted. The format of the following address packet determines
whether master transmitter or master receiver mode is to be entered. If SLA+W is transmitted, MT mode is entered, if SLA+R
is transmitted, MR mode is entered. All the status codes mentioned in this section assume that the prescaler bits are zero or
are masked to zero.
Figure 21-13. Data Transfer in Master Receiver Mode
V
CC
Device 1
Master
Receiver
Device 2
Slave
Transmitter
Device 3 ........ Device n
R1
R2
SDA
SCL
A START condition is sent by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
1
0
X
1
0
X
TWEN must be written to one to enable the 2-wire serial interface, TWSTA must be written to one to transmit a START
condition and TWINT must be set to clear the TWINT flag. The TWI will then test the 2-wire serial bus and generate a
START condition as soon as the bus becomes free. After a START condition has been transmitted, the TWINT flag is set by
hardware, and the status code in TWSR will be 0x08 (See Table 21-3 on page 188). In order to enter MR mode, SLA+R must
be transmitted. This is done by writing SLA+R to TWDR. Thereafter the TWINT bit should be cleared (by writing it to one) to
continue the transfer. This is accomplished by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
0
0
X
1
0
X
When SLA+R have been transmitted and an acknowledgement bit has been received, TWINT is set again and a number of
status codes in TWSR are possible. Possible status codes in master mode are 0x38, 0x40, or 0x48. The appropriate action
to be taken for each of these status codes is detailed in Table 21-4 on page 191. Received data can be read from the TWDR
register when the TWINT flag is set high by hardware. This scheme is repeated until the last byte has been received. After
the last byte has been received, the MR should inform the ST by sending a NACK after the last received data byte. The
transfer is ended by generating a STOP condition or a repeated START condition.
A STOP condition is generated by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
0
1
X
1
0
X
A REPEATED START condition is generated by writing the following value to TWCR:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
1
X
1
0
X
1
0
X
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After a repeated START condition (state 0x10) the 2-wire serial interface can access the same slave again, or a new slave
without transmitting a STOP condition. Repeated START enables the master to switch between slaves, master transmitter
mode and master receiver mode without losing control over the bus.
Table 21-4. Status codes for Master Receiver Mode
Application Software Response
Status Code Status of the 2-wire
(TWSR)
Prescaler
Bits are 0
Serial Bus and 2-wire
Serial Interface
Hardware
To/from TWDR
To TWCR
STA STO TWINT TWEA Next Action Taken by TWI Hardware
0x08
A START condition has Load SLA+R
been transmitted
0
0
1
X
SLA+R will be transmitted
ACK or NOT ACK will be received
0x10
A repeated START
condition has been
transmitted
Load SLA+R or
0
0
0
0
1
1
X
X
SLA+R will be transmitted ACK or NOT ACK
will be received
SLA+W will be transmitted logic will switch to
master transmitter mode
Load SLA+W
0x38
0x40
0x48
Arbitration lost in SLA+R No TWDR action or
or NOT ACK bit
0
1
0
0
1
1
X
X
2-wire serial bus will be released and not
addressed slave mode will be entered
A START condition will be transmitted when
the bus becomes free
No TWDR action
SLA+R has been
transmitted; ACK has
been received
No TWDR action or
No TWDR action
0
0
0
0
1
1
0
1
Data byte will be received and NOT ACK will
be returned
Data byte will be received and ACK will be
returned
SLA+R has been
No TWDR action or
1
0
0
1
1
1
X
X
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
transmitted; NOT ACK No TWDR action or
has been received
No TWDR action
1
1
1
X
STOP condition followed by a START
condition will be transmitted and TWSTO flag
will be reset
0x50
0x58
Data byte has been
received; ACK has been Read data byte
returned
Read data byte or
0
0
0
0
1
1
0
1
Data byte will be received and NOT ACK will
be returned
Data byte will be received and ACK will be
returned
Data byte has been
received; NOT ACK has Read data byte or
been returned
Read data byte or
1
0
0
1
1
1
X
X
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
Read data byte
1
1
1
X
STOP condition followed by a START
condition will be transmitted and TWSTO flag
will be reset
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Figure 21-14. Formats and States in the Master Receiver Mode
MR
Successfull
S
SLA
R
A
DATA
A
DATA
A
P
reception
from a slave
receiver
$08
$40
$50
$58
Next transfer
started with a
repeated start
condition
R
SLA
R
S
$10
Not acknowledge
received after the
slave address
A
P
W
$48
MT
Arbitration lost in slave
address or data byte
Other master
continues
Other master
continues
A or A
A or A
$38
$38
A
Arbitration lost and
addressed as slave
Other master
continues
To corresponding
states in slave mode
$68
$78
$B0
Any number of data bytes
From master to slave
From slave to master
DATA
A
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the Two-Wire Serial Bus.
The prescaler bits are zero or masked to zero
n
21.7.3 Slave Receiver Mode
In the slave receiver mode, a number of data bytes are received from a master transmitter (see Figure 21-15). All the status
codes mentioned in this section assume that the prescaler bits are zero or are masked to zero.
Figure 21-15. Data Transfer in Slave Receiver Mode
VCC
Device 1
Slave
Receiver
Device 2
Master
Transmitter
Device 3 ........ Device n
R1
R2
SDA
SCL
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To initiate the slave receiver mode, TWAR and TWCR must be initialized as follows:
TWAR
TWA6
TWA5
TWA4
TWA3
TWA2
TWA1
TWA0
TWGCE
value
Device’s Own Slave Address
The upper 7 bits are the address to which the 2-wire serial interface will respond when addressed by a master. If the LSB is
set, the TWI will respond to the general call address (0x00), otherwise it will ignore the general call address.
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
0
1
0
0
0
1
0
X
TWEN must be written to one to enable the TWI. The TWEA bit must be written to one to enable the acknowledgement of
the device’s own slave address or the general call address. TWSTA and TWSTO must be written to zero.
When TWAR and TWCR have been initialized, the TWI waits until it is addressed by its own slave address (or the general
call address if enabled) followed by the data direction bit. If the direction bit is “0” (write), the TWI will operate in SR mode,
otherwise ST mode is entered. After its own slave address and the write bit have been received, the TWINT flag is set and a
valid status code can be read from TWSR. The status code is used to determine the appropriate software action. The
appropriate action to be taken for each status code is detailed in Table 21-5 on page 193. The slave receiver mode may also
be entered if arbitration is lost while the TWI is in the master mode (see states 0x68 and 0x78).
If the TWEA bit is reset during a transfer, the TWI will return a “not acknowledge” (“1”) to SDA after the next received data
byte. This can be used to indicate that the slave is not able to receive any more bytes. While TWEA is zero, the TWI does not
acknowledge its own slave address. However, the 2-wire serial bus is still monitored and address recognition may resume at
any time by setting TWEA. This implies that the TWEA bit may be used to temporarily isolate the TWI from the 2-wire serial
bus.
In all sleep modes other than idle mode, the clock system to the TWI is turned off. If the TWEA bit is set, the interface can still
acknowledge its own slave address or the general call address by using the 2-wire serial bus clock as a clock source. The
part will then wake up from sleep and the TWI will hold the SCL clock low during the wake up and until the TWINT flag is
cleared (by writing it to one). Further data reception will be carried out as normal, with the AVR® clocks running as normal.
Observe that if the AVR is set up with a long start-up time, the SCL line may be held low for a long time, blocking other data
transmissions. Note that the 2-wire serial interface data register – TWDR does not reflect the last byte present on the bus
when waking up from these sleep modes.
Table 21-5. Status Codes for Slave Receiver Mode
Application Software Response
Status Code
(TWSR)
To/from TWDR
To TWCR
Status of the 2-wire
Prescaler
Serial Bus and 2-wire
Bits are 0 Serial Interface Hardware
STA STO TWINT TWEA
Next Action Taken by TWI Hardware
0x60
Own SLA+W has been
received; ACK has been
returned
No TWDR action or
No TWDR action
X
0
1
0
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
X
0
1
1
0x68
Arbitration lost in
No TWDR action or
No TWDR action
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
SLA+R/W as master; own
SLA+W has been
received; ACK has been
returned
0x70
0x78
General call address has No TWDR action or
been received; ACK has
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
been returned
No TWDR action
Arbitration lost in
No TWDR action or
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
SLA+R/W as master;
general call address has
been received; ACK has
been returned
No TWDR action
0x80
Previously addressed with Read data byte or
own SLA+W; data has
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
been received; ACK has
been returned
Read data byte
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Table 21-5. Status Codes for Slave Receiver Mode (Continued)
Application Software Response
Status Code
(TWSR)
To/from TWDR
To TWCR
Status of the 2-wire
Prescaler
Serial Bus and 2-wire
Bits are 0 Serial Interface Hardware
STA STO TWINT TWEA
Next Action Taken by TWI Hardware
0x88
Previously addressed with Read data byte or
own SLA+W; data has
been received; NOT ACK Read data byte or
has been returned
0
0
1
0
Switched to the not addressed slave
mode; no recognition of own SLA or GCA
Switched to the not addressed slave
mode; own SLA will be recognized;
GCA will be recognized if TWGCE = “1”
Switched to the not addressed slave
mode; no recognition of own SLA or GCA;
a START condition will be transmitted
when the bus becomes free
Switched to the not addressed slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”; a
START condition will be transmitted when
the bus becomes free
0
0
1
1
Read data byte or
1
1
0
0
1
1
0
1
Read data byte
0x90
0x98
Previously addressed with Read data byte or
general call; data has been
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
received; ACK has been
returned
Read data byte
Previously addressed with Read data byte or
general call; data has been
0
0
0
0
1
1
0
1
Switched to the not addressed slave
mode; no recognition of own SLA or GCA
Switched to the not addressed slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”
Switched to the not addressed slave
mode; no recognition of own SLA or GCA;
a START condition will be transmitted
when the bus becomes free
Switched to the not addressed slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”; a
START condition will be transmitted when
the bus becomes free
received; NOT ACK has
been returned
Read data byte or
Read data byte or
1
1
0
0
1
1
0
1
Read data byte
No action
0xA0
A STOP condition or
0
0
0
0
1
1
0
1
Switched to the not addressed slave
mode; no recognition of own SLA or GCA
Switched to the not addressed slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”
Switched to the not addressed slave
mode; no recognition of own SLA or GCA;
a START condition will be transmitted
when the bus becomes free
Switched to the not addressed slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”; a
START condition will be transmitted when
the bus becomes free
repeated START condition
has been received while
still addressed as slave
1
1
0
0
1
1
0
1
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Figure 21-16. Formats and States in the Slave Receiver Mode
Reception of the own
S
SLA
W
A
DATA
A
DATA
A
P or S
slave address and one or
more data bytes. All are
acknowledged
$60
$80
$80
A
$A0
Last data byte received
is not acknowledged
P or S
$88
Arbitration lost as master
and addressed as slave
A
$68
A
Reception of the general call
address and one or more
data bytes
General Call
DATA
A
DATA
A
P or S
$70
$90
$90
A
$A0
Last data byte received
is not acknowledged
P or S
$98
Arbitration lost as master
and as slave by general call
A
$78
Any number of data bytes
and their associated acknowledge bits
From master to slave
From slave to master
DATA
A
This number (contained in TWSR) corresponds
to a defined state of the Two-Wire Serial Bus.
The prescaler bits are zero or masked to zero
n
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21.7.4 Slave Transmitter Mode
In the slave transmitter mode, a number of data bytes are transmitted to a master receiver (see Figure 21-17). All the status
codes mentioned in this section assume that the prescaler bits are zero or are masked to zero.
Figure 21-17. Data Transfer in Slave Transmitter Mode
VCC
Device 1
Slave
Transmitter
Device 2
Master
Receiver
Device 3 ........ Device n
R1
R2
SDA
SCL
To initiate the slave transmitter mode, TWAR and TWCR must be initialized as follows:
TWAR
TWA6
TWA5
TWA4
TWA3
TWA2
TWA1
TWA0
TWGCE
value
Device’s Own Slave Address
The upper seven bits are the address to which the 2-wire serial interface will respond when addressed by a master. If the
LSB is set, the TWI will respond to the general call address (0x00), otherwise it will ignore the general call address.
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
value
0
1
0
0
0
1
0
X
TWEN must be written to one to enable the TWI. The TWEA bit must be written to one to enable the acknowledgement of
the device’s own slave address or the general call address. TWSTA and TWSTO must be written to zero.
When TWAR and TWCR have been initialized, the TWI waits until it is addressed by its own slave address (or the general
call address if enabled) followed by the data direction bit. If the direction bit is “1” (read), the TWI will operate in ST mode,
otherwise SR mode is entered. After its own slave address and the write bit have been received, the TWINT flag is set and a
valid status code can be read from TWSR. The status code is used to determine the appropriate software action. The
appropriate action to be taken for each status code is detailed in Table 21-6 on page 197. The slave transmitter mode may
also be entered if arbitration is lost while the TWI is in the master mode (see state 0xB0).
If the TWEA bit is written to zero during a transfer, the TWI will transmit the last byte of the transfer. State 0xC0 or state 0xC8
will be entered, depending on whether the master receiver transmits a NACK or ACK after the final byte. The TWI is
switched to the not addressed slave mode, and will ignore the master if it continues the transfer. Thus the master receiver
receives all “1” as serial data. State 0xC8 is entered if the master demands additional data bytes (by transmitting ACK), even
though the slave has transmitted the last byte (TWEA zero and expecting NACK from the master).
While TWEA is zero, the TWI does not respond to its own slave address. However, the 2-wire serial bus is still monitored
and address recognition may resume at any time by setting TWEA. This implies that the TWEA bit may be used to
temporarily isolate the TWI from the 2-wire serial bus.
In all sleep modes other than Idle mode, the clock system to the TWI is turned off. If the TWEA bit is set, the interface can
still acknowledge its own slave address or the general call address by using the 2-wire serial bus clock as a clock source.
The part will then wake up from sleep and the TWI will hold the SCL clock will low during the wake up and until the TWINT
flag is cleared (by writing it to one). Further data transmission will be carried out as normal, with the AVR® clocks running as
normal. Observe that if the AVR is set up with a long start-up time, the SCL line may be held low for a long time, blocking
other data transmissions.
Note that the 2-wire serial interface data register – TWDR does not reflect the last byte present on the bus when waking up
from these sleep modes.
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Table 21-6. Status Codes for Slave Transmitter Mode
Application Software Response
Status
Code
To/from TWDR
To TWCR
(TWSR)
Prescaler
Bits are 0
Status of the 2-wire Serial
Bus and 2-wire Serial
Interface Hardware
STA STO TWINT TWEA
Next Action Taken by TWI Hardware
0xA8
0xB0
0xB8
0xC0
Own SLA+R has been
received; ACK has been
returned
Load data byte or
Load data byte
X
0
1
0
Last data byte will be transmitted and NOT
ACK should be received
Data byte will be transmitted and ACK
should be received
X
0
1
1
Arbitration lost in SLA+R/W Load data byte or
as master; own SLA+R has
been received; ACK has
been returned
X
X
0
0
1
1
0
1
Last data byte will be transmitted and NOT
ACK should be received
Data byte will be transmitted and ACK
should be received
Load data byte
Data byte in TWDR has
been transmitted; ACK has
been received
Load data byte or
Load data byte
X
X
0
0
1
1
0
1
Last data byte will be transmitted and NOT
ACK should be received
Data byte will be transmitted and ACK
should be received
Data byte in TWDR has
been transmitted; NOT
ACK has been received
No TWDR action or
No TWDR action or
0
0
0
0
1
1
0
1
Switched to the not addressed slave mode;
no recognition of own SLA or GCA
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”
No TWDR action or
No TWDR action
1
1
0
0
1
1
0
1
Switched to the not addressed slave mode;
no recognition of own SLA or GCA; a
START condition will be transmitted when
the bus becomes free
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”; a START
condition will be transmitted when the bus
becomes free
0xC8
Last data byte in TWDR
has been transmitted
(TWEA = “0”); ACK has
been received
No TWDR action or
No TWDR action or
0
0
0
0
1
1
0
1
Switched to the not addressed slave mode;
no recognition of own SLA or GCA
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”
No TWDR action or
No TWDR action
1
1
0
0
1
1
0
1
Switched to the not addressed slave mode;
no recognition of own SLA or GCA; a
START condition will be transmitted when
the bus becomes free
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”; a START
condition will be transmitted when the bus
becomes free
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Figure 21-18. Formats and States in the Slave Transmitter Mode
Reception of the own
slave address and one
or more data bytes
S
SLA
R
A
DATA
A
DATA
A
P or S
$A8
$B8
$C0
Arbitration lost as master
and addressed as slave
A
$B0
Last data byte transmitted.
Switched to not adressed
slave (TWEA = “0”
A
All 1’s
P or S
$C8
Any number of data bytes
and their associated acknowledge bits
From master to slave
From slave to master
DATA
A
This number (contained in TWSR) corresponds
to a defined state of the Two-Wire Serial Bus.
The prescaler bits are zero or masked to zero
n
21.7.5 Miscellaneous States
There are two status codes that do not correspond to a defined TWI state, see Table 21-7.
Status 0xF8 indicates that no relevant information is available because the TWINT flag is not set. This occurs between other
states, and when the TWI is not involved in a serial transfer.
Status 0x00 indicates that a bus error has occurred during a 2-wire serial bus transfer. A bus error occurs when a START or
STOP condition occurs at an illegal position in the format frame. Examples of such illegal positions are during the serial
transfer of an address byte, a data byte, or an acknowledge bit. When a bus error occurs, TWINT is set. To recover from a
bus error, the TWSTO flag must set and TWINT must be cleared by writing a logic one to it. This causes the TWI to enter the
not addressed Slave mode and to clear the TWSTO flag (no other bits in TWCR are affected). The SDA and SCL lines are
released, and no STOP condition is transmitted.
Table 21-7. Miscellaneous States
Application Software Response
Status Code
(TWSR)
Prescaler
Bits are 0
Status of the 2-wire
Serial Bus and 2-wire
Serial Interface
Hardware
To/from TWDR
To TWCR
STA STO TWINT TWEA
Next Action Taken by TWI Hardware
0xF8
No relevant state
information available;
TWINT = “0”
No TWDR action
No TWCR action
Wait or proceed current transfer
0x00
Bus error due to an illegal No TWDR action
START or STOP condition
0
1
1
X
Only the internal hardware is affected, no
STOP condition is sent on the bus. In all
cases, the bus is released and TWSTO is
cleared.
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21.7.6 Combining Several TWI Modes
In some cases, several TWI modes must be combined in order to complete the desired action. Consider for example reading
data from a serial EEPROM. Typically, such a transfer involves the following steps:
1. The transfer must be initiated.
2. The EEPROM must be instructed what location should be read.
3. The reading must be performed.
4. The transfer must be finished.
Note that data is transmitted both from master to slave and vice versa. The master must instruct the slave what location it
wants to read, requiring the use of the MT mode. Subsequently, data must be read from the slave, implying the use of the
MR mode. Thus, the transfer direction must be changed. The master must keep control of the bus during all these steps, and
the steps should be carried out as an atomical operation. If this principle is violated in a multi master system, another master
can alter the data pointer in the EEPROM between steps 2 and 3, and the master will read the wrong data location. Such a
change in transfer direction is accomplished by transmitting a REPEATED START between the transmission of the address
byte and reception of the data. After a REPEATED START, the master keeps ownership of the bus. The following figure
shows the flow in this transfer.
Figure 21-19. Combining Several TWI Modes to Access a Serial EEPROM
Master Transmitter
Master Receiver
DATA
S
SLA + W
S = START
Transmitted from master to slave
A
ADDRESS
A
RS
S = REPEATED START
Transmitted from slave to master
SLA + R
A
A
P
R
P = STOP
21.8 Multi-master Systems and Arbitration
If multiple masters are connected to the same bus, transmissions may be initiated simultaneously by one or more of them.
The TWI standard ensures that such situations are handled in such a way that one of the masters will be allowed to proceed
with the transfer, and that no data will be lost in the process. An example of an arbitration situation is depicted below, where
two masters are trying to transmit data to a slave receiver.
Figure 21-20. An Arbitration Example
V
CC
Device 1
Master
Transmitter
Device 2
Master
Transmitter
Device 3
Slave
Receiver
........ Device n
R1
R2
SDA
SCL
Several different scenarios may arise during arbitration, as described below:
●
Two or more masters are performing identical communication with the same slave. In this case, neither the slave nor
any of the masters will know about the bus contention.
●
Two or more masters are accessing the same slave with different data or direction bit. In this case, arbitration will
occur, either in the READ/WRITE bit or in the data bits. The masters trying to output a one on SDA while another
master outputs a zero will lose the arbitration. Losing masters will switch to not addressed slave mode or wait until the
bus is free and transmit a new START condition, depending on application software action.
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●
Two or more masters are accessing different slaves. In this case, arbitration will occur in the SLA bits. Masters trying
to output a one on SDA while another master outputs a zero will lose the arbitration. Masters losing arbitration in SLA
will switch to slave mode to check if they are being addressed by the winning master. If addressed, they will switch to
SR or ST mode, depending on the value of the READ/WRITE bit. If they are not being addressed, they will switch to
not addressed slave mode or wait until the bus is free and transmit a new START condition, depending on application
software action.
This is summarized in Figure 21-21. Possible status values are given in circles.
Figure 21-21. Possible Status Codes Caused by Arbitration
START
SLA
DATA
STOP
Arbitration lost in SLA
Arbitration lost in DATA
Own
NO
TWI bus will be released and not addressed slave mode will be entered
A START condition will be transmitted when the bus becomes free
38
Address/ General Call
received
YES
68/78
B0
Write
Data byte will be received and NOT ACK will be returned
Data byte will be received and ACK will be returned
Direction
Read
Last data byte will be transmitted and NOT ACK should be received
Data byte will be transmitted and ACK should be received
21.9 Register Description
21.9.1 TWBR – TWI Bit Rate Register
Bit
7
6
5
4
3
2
1
0
(0xB8)
TWBR7 TWBR6 TWBR5 TWBR4 TWBR3 TWBR2 TWBR1 TWBR0
TWBR
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
• Bits 7:0 – TWI Bit Rate Register
TWBR selects the division factor for the bit rate generator. The bit rate generator is a frequency divider which generates the
SCL clock frequency in the master modes. See Section 21.5.2 “Bit Rate Generator Unit” on page 182 for calculating bit
rates.
21.9.2 TWCR – TWI Control Register
Bit
7
TWINT
R/W
0
6
TWEA
R/W
0
5
4
3
2
TWEN
R/W
0
1
–
0
TWIE
R/W
0
(0xBC)
TWSTA TWSTO
TWWC
TWCR
Read/Write
Initial Value
R/W
0
R/W
0
R
0
R
0
The TWCR is used to control the operation of the TWI. It is used to enable the TWI, to initiate a master access by applying a
START condition to the bus, to generate a receiver acknowledge, to generate a stop condition, and to control halting of the
bus while the data to be written to the bus are written to the TWDR. It also indicates a write collision if data is attempted
written to TWDR while the register is inaccessible.
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• Bit 7 – TWINT: TWI Interrupt Flag
This bit is set by hardware when the TWI has finished its current job and expects application software response. If the I-bit in
SREG and TWIE in TWCR are set, the MCU will jump to the TWI interrupt vector. While the TWINT flag is set, the SCL low
period is stretched. The TWINT flag must be cleared by software by writing a logic one to it. Note that this flag is not
automatically cleared by hardware when executing the interrupt routine. Also note that clearing this flag starts the operation
of the TWI, so all accesses to the TWI address register (TWAR), TWI status register (TWSR), and TWI data register (TWDR)
must be complete before clearing this flag.
• Bit 6 – TWEA: TWI Enable Acknowledge Bit
The TWEA bit controls the generation of the acknowledge pulse. If the TWEA bit is written to one, the ACK pulse is
generated on the TWI bus if the following conditions are met:
1. The device’s own slave address has been received.
2. A general call has been received, while the TWGCE bit in the TWAR is set.
3. A data byte has been received in master receiver or slave receiver mode.
By writing the TWEA bit to zero, the device can be virtually disconnected from the 2-wire serial bus temporarily. Address
recognition can then be resumed by writing the TWEA bit to one again.
• Bit 5 – TWSTA: TWI START Condition Bit
The application writes the TWSTA bit to one when it desires to become a master on the 2-wire serial bus. The TWI hardware
checks if the bus is available, and generates a START condition on the bus if it is free. However, if the bus is not free, the
TWI waits until a STOP condition is detected, and then generates a new START condition to claim the bus master status.
TWSTA must be cleared by software when the START condition has been transmitted.
• Bit 4 – TWSTO: TWI STOP Condition Bit
Writing the TWSTO bit to one in master mode will generate a STOP condition on the 2-wire serial bus. When the STOP
condition is executed on the bus, the TWSTO bit is cleared automatically. In slave mode, setting the TWSTO bit can be used
to recover from an error condition. This will not generate a STOP condition, but the TWI returns to a well-defined
unaddressed slave mode and releases the SCL and SDA lines to a high impedance state.
• Bit 3 – TWWC: TWI Write Collision Flag
The TWWC bit is set when attempting to write to the TWI data register – TWDR when TWINT is low. This flag is cleared by
writing the TWDR register when TWINT is high.
• Bit 2 – TWEN: TWI Enable Bit
The TWEN bit enables TWI operation and activates the TWI interface. When TWEN is written to one, the TWI takes control
over the I/O pins connected to the SCL and SDA pins, enabling the slew-rate limiters and spike filters. If this bit is written to
zero, the TWI is switched off and all TWI transmissions are terminated, regardless of any ongoing operation.
• Bit 1 – Reserved
This bit is a reserved bit and will always read as zero.
• Bit 0 – TWIE: TWI Interrupt Enable
When this bit is written to one, and the I-bit in SREG is set, the TWI interrupt request will be activated for as long as the
TWINT flag is high.
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21.9.3 TWSR – TWI Status Register
Bit
7
TWS7
R
6
TWS6
R
5
TWS5
R
4
TWS4
R
3
TWS3
R
2
–
1
TWPS1
R/W
0
0
TWPS0
R/W
0
(0xB9)
TWSR
Read/Write
Initial Value
R
0
1
1
1
1
1
• Bits 7:3 – TWS: TWI Status
These 5 bits reflect the status of the TWI logic and the 2-wire serial bus. The different status codes are described Section
21.7 “Transmission Modes” on page 186. Note that the value read from TWSR contains both the 5-bit status value and the
2-bit prescaler value. The application designer should mask the prescaler bits to zero when checking the status bits. This
makes status checking independent of prescaler setting. This approach is used in this datasheet, unless otherwise noted.
• Bit 2 – Reserved
This bit is reserved and will always read as zero.
• Bits 1:0 – TWPS: TWI Prescaler Bits
These bits can be read and written, and control the bit rate prescaler.
Table 21-8. TWI Bit Rate Prescaler
TWPS1
TWPS0
Prescaler Value
0
0
1
1
0
1
0
1
1
4
16
64
To calculate bit rates, see Section 21.5.2 “Bit Rate Generator Unit” on page 182. The value of TWPS1..0 is used in the
equation.
21.9.4 TWDR – TWI Data Register
Bit
7
TWD7
R/W
1
6
TWD6
R/W
1
5
TWD5
R/W
1
4
TWD4
R/W
1
3
TWD3
R/W
1
2
TWD2
R/W
1
1
TWD1
R/W
1
0
TWD0
R/W
1
(0xBB)
TWDR
Read/Write
Initial Value
In transmit mode, TWDR contains the next byte to be transmitted. In receive mode, the TWDR contains the last byte
received. It is writable while the TWI is not in the process of shifting a byte. This occurs when the TWI interrupt flag (TWINT)
is set by hardware. Note that the data register cannot be initialized by the user before the first interrupt occurs. The data in
TWDR remains stable as long as TWINT is set. While data is shifted out, data on the bus is simultaneously shifted in. TWDR
always contains the last byte present on the bus, except after a wake up from a sleep mode by the TWI interrupt. In this
case, the contents of TWDR is undefined. In the case of a lost bus arbitration, no data is lost in the transition from master to
slave. Handling of the ACK bit is controlled automatically by the TWI logic, the CPU cannot access the ACK bit directly.
• Bits 7:0 – TWD: TWI Data Register
These eight bits constitute the next data byte to be transmitted, or the latest data byte received on the 2-wire serial bus.
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21.9.5 TWAR – TWI (Slave) Address Register
Bit
7
TWA6
R/W
1
6
TWA5
R/W
1
5
TWA4
R/W
1
4
TWA3
R/W
1
3
TWA2
R/W
1
2
TWA1
R/W
1
1
TWA0
R/W
1
0
TWGCE
R/W
0
(0xBA)
TWAR
Read/Write
Initial Value
The TWAR should be loaded with the 7-bit slave address (in the seven most significant bits of TWAR) to which the TWI will
respond when programmed as a slave transmitter or receiver, and not needed in the master modes. In multi master
systems, TWAR must be set in masters which can be addressed as Slaves by other masters.
The LSB of TWAR is used to enable recognition of the general call address (0x00). There is an associated address
comparator that looks for the slave address (or general call address if enabled) in the received serial address. If a match is
found, an interrupt request is generated.
• Bits 7:1 – TWA: TWI (Slave) Address Register
These seven bits constitute the slave address of the TWI unit.
• Bit 0 – TWGCE: TWI General Call Recognition Enable Bit
If set, this bit enables the recognition of a general call given over the 2-wire serial bus.
21.9.6 TWAMR – TWI (Slave) Address Mask Register
Bit
7
6
5
4
TWAM[6:0]
R/W
3
2
1
0
–
(0xBD)
TWAMR
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R
0
0
• Bits 7:1 – TWAM: TWI Address Mask
The TWAMR can be loaded with a 7-bit Slave Address mask. Each of the bits in TWAMR can mask (disable) the
corresponding address bit in the TWI Address Register (TWAR). If the mask bit is set to one then the address match logic
ignores the compare between the incoming address bit and the corresponding bit in TWAR. Figure 21-22 shows the address
match logic in detail.
Figure 21-22. TWI Address Match Logic, Block Diagram
TWAR0
Address
Match
Address
Bit 0
TWAMR0
Address Bit Comparator 0
Address Bit Comparator 6 to 1
• Bit 0 – Reserved
This bit is reserved and will always read as zero.
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22. AC - Analog Comparator
22.1 Overview
The analog comparator compares the input values on the positive pin AIN0 and negative pin AIN1. When the voltage on the
positive pin AIN0 is higher than the voltage on the negative pin AIN1, the analog comparator output, ACO, is set. The
comparator’s output can be set to trigger the Timer/Counter1 input capture function. In addition, the comparator can trigger a
separate interrupt, exclusive to the analog comparator. The user can select interrupt triggering on comparator output rise, fall
or toggle. A block diagram of the comparator and its surrounding logic is shown in Figure 22-1.
The power reduction ADC bit, PRADC, in Section 10.12.3 “PRR0 – Power Reduction Register 0” on page 39 must be
disabled by writing a logical zero to be able to use the ADC input MUX.
Figure 22-1. Analog Comparator Block Diagram(2)
VCC
Bandgap
Reference
ACBG
ACD
ACIE
AIN0
AIN1
Analog
Comparator
IRQ
+
Interrupt
Select
-
ACI
ACIS1
ACIS0
ACIC
ACO
ACME
ADEN
To T/C1 Capture
Trigger MUX
ADC Multiplexer
Output(1)
Notes: 1. See Table 22-1 on page 205.
2. Refer to Figure 1-1 on page 3 and Table 14-5 on page 64 for analog comparator pin placement.
22.2 Analog Comparator Multiplexed Input
It is possible to select any of the ADC7..0 pins to replace the negative input to the analog comparator. The ADC multiplexer
is used to select this input, and consequently, the ADC must be switched off to utilize this feature. If the analog comparator
multiplexer enable bit (ACME in ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX2..0 in
ADMUX select the input pin to replace the negative input to the analog comparator, as shown in Table 22-1 on page 205. If
ACME is cleared or ADEN is set, AIN1 is applied to the negative input to the analog comparator.
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Table 22-1. Analog Comparator Mulitiplexed Input
ACME
ADEN
MUX2..0
xxx
Analog Comparator Negative Input
0
1
1
1
1
1
1
1
1
1
x
1
0
0
0
0
0
0
0
0
AIN1
AIN1
xxx
000
001
010
011
ADC0
ADC1
ADC2
ADC3
ADC4
ADC5
ADC6
ADC7
100
101
110
111
22.3 Register Description
22.3.1 ADCSRB – ADC Control and Status Register B
Bit
7
–
6
ACME
R/W
0
5
–
4
–
3
-
2
ADTS2
R/W
0
1
ADTS1
R/W
0
0
ADTS0
R/W
0
(0x7B)
ADCSRB
Read/Write
Initial Value
R
0
R
0
R
0
R
0
• Bit 6 – ACME: Analog Comparator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the ADC multiplexer selects the
negative input to the analog comparator. When this bit is written logic zero, AIN1 is applied to the negative input of the
analog comparator. For a detailed description of this bit, see Section 22.2 “Analog Comparator Multiplexed Input” on page
204.
22.3.2 ACSR – Analog Comparator Control and Status Register
Bit
7
6
ACBG
R/W
0
5
ACO
R
4
ACI
R/W
0
3
ACIE
R/W
0
2
ACIC
R/W
0
1
ACIS1
R/W
0
0
ACIS0
R/W
0
0x30 (0x50)
Read/Write
Initial Value
ACD
R/W
0
ACSR
N/A
• Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the analog comparator is switched off. This bit can be set at any time to turn
off the analog comparator. This will reduce power consumption in active and idle mode. When changing the ACD bit, the
analog comparator interrupt must be disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the
bit is changed.
• Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set, a fixed bandgap reference voltage replaces the positive input to the analog comparator. When this bit is
cleared, AIN0 is applied to the positive input of the analog comparator. When bandgap reference is used as input to the
analog comparator, it will take a certain time for the voltage to stabilize. If not stabilized, the first conversion may give wrong
value. See Section 11.2 “Internal Voltage Reference” on page 43.
• Bit 5 – ACO: Analog Comparator Output
The output of the analog comparator is synchronized and then directly connected to ACO. The synchronization introduces a
delay of 1 - 2 clock cycles.
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• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined by ACIS1 and ACIS0. The
analog comparator interrupt routine is executed if the ACIE bit is set and the I-bit in SREG is set. ACI is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the status register is set, the analog comparator interrupt is activated.
When written logic zero, the interrupt is disabled.
• Bit 2 – ACIC: Analog Comparator Input Capture Enable
When written logic one, this bit enables the input capture function in Timer/Counter1 to be triggered by the analog
comparator. The comparator output is in this case directly connected to the input capture front-end logic, making the
comparator utilize the noise canceler and edge select features of the Timer/Counter1 input capture interrupt. When written
logic zero, no connection between the analog comparator and the input capture function exists. To make the comparator
trigger the Timer/Counter1 input capture interrupt, the ICIE1 bit in the timer interrupt mask register (TIMSK1) must be set.
• Bits 1:0 – ACIS1:ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the analog comparator interrupt. The different settings are shown
in Table 22-2.
Table 22-2. ACIS1/ACIS0 Settings
ACIS1
ACIS0
Interrupt Mode
0
0
1
1
0
1
0
1
Comparator interrupt on output toggle.
Reserved
Comparator interrupt on falling output edge.
Comparator interrupt on rising output edge.
When changing the ACIS1/ACIS0 bits, the analog comparator Interrupt must be disabled by clearing its interrupt enable bit
in the ACSR register. Otherwise an interrupt can occur when the bits are changed.
22.3.3 DIDR1 – Digital Input Disable Register 1
Bit
7
–
6
–
5
–
4
–
3
–
2
–
1
AIN1D
R/W
0
0
AIN0D
R/W
0
(0x7F)
DIDR1
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R
0
R
0
• Bit 1:0 – AIN1D:AIN0D: AIN1:AIN0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the AIN1/0 pin is disabled. The corresponding PIN register bit will
always read as zero when this bit is set. When an analog signal is applied to the AIN1/0 pin and the digital input from this pin
is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer.
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23. ADC - Analog-to-digital Converter
23.1 Features
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
10-bit resolution
0.5 LSB integral non-linearity
±2 LSB absolute accuracy
65 - 260µs conversion time
Up to 15kSPS at maximum resolution
8 multiplexed single ended input channels
Differential mode with selectable gain at 1x, 10x or 200x
Optional left adjustment for ADC result readout
0 - VCC ADC input voltage range
2.7 - VCC differential ADC voltage range
Selectable 2.56V or 1.1V ADC reference voltage
Free running or single conversion mode
ADC start conversion by auto triggering on interrupt sources
Interrupt on ADC conversion complete
Sleep mode noise canceler
23.2 Overview
The Atmel® ATmega164P-B/324P-B/644P-B features a 10-bit successive approximation ADC. The ADC is connected to an
8-channel analog multiplexer which allows 8 single-ended voltage inputs constructed from the pins of Port A.
The single-ended voltage inputs refer to 0V (GND).
The device also supports 16 differential voltage input combinations. Two of the differential inputs (ADC1, ADC0 and ADC3,
ADC2) are equipped with a programmable gain stage. This provides amplification steps of 0 dB (1x), 20 dB (10x), or 46 dB
(200x) on the differential input voltage before the A/D conversion. Seven differential analog input channels share a common
negative terminal (ADC1), while any other ADC input can be selected as the positive input terminal. If 1x or 10x gain is used,
8-bit resolution can be expected. If 200x gain is used, 6-bit resolution can be expected. Note that internal references of 1.1V
should not be used on 10x and 200x gain.
The ADC contains a sample and hold circuit which ensures that the input voltage to the ADC is held at a constant level
during conversion. A block diagram of the ADC is shown in Figure 23-1 on page 208.
The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ±0.3 V from VCC. See the
Section 23.7 “ADC Noise Canceler” on page 214 on how to connect this pin.
Internal reference voltages of nominally 1.1V, 2.56V or AVCC are provided On-chip. The voltage reference may be
externally decoupled at the AREF pin by a capacitor for better noise performance.
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Figure 23-1. Analog-to-digital Converter Block Schematic
ADC Conversion
Complete IRQ
Interrupt
Flags
ADTS[2:0]
15
0
ADC Multiplexer
Select (ADMUX)
ADC CTRL and Status
Register B (ADCSRB)
ADC CTRL and Status
Register A (ADCSRA)
ADC Data Register
(ADCH/ADCL)
Trigger
Select
START
Prescaler
MUX Decoder
AVCC
Conversion Logic
Internal
Reference
(1.1V/2.56V)
AREF
10-bit DAC
-
+
Sample and Hold
Comparator
NEG
INPUT
MUX
ADC[2:0]
-
+
Gain
Amplifier
ADC[7:09
Bandgap
Reference
(1.1V)
ADC
MULTIPLEXER
OUTPUT
POS
INPUT
MUX
GND
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23.3 Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The minimum value
represents GND and the maximum value represents the voltage on the AREF pin minus 1 LSB. Optionally, AVCC or an
internal 2.56V reference voltage may be connected to the AREF pin by writing to the REFSn bits in the ADMUX register. The
internal voltage reference may thus be decoupled by an external capacitor at the AREF pin to improve noise immunity.
The analog input channel and differential gain are selected by writing to the MUX bits in ADMUX. Any of the ADC input pins,
as well as GND and a fixed bandgap voltage reference, can be selected as single ended inputs to the ADC. A selection of
ADC input pins can be selected as positive and negative inputs to the differential gain amplifier.
If differential channels are selected, the differential gain stage amplifies the voltage difference between the selected input
channel pair by the selected gain factor. This amplified value then becomes the analog input to the ADC. If single ended
channels are used, the gain amplifier is bypassed altogether.
The ADC is enabled by setting the ADC enable bit, ADEN in ADCSRA. Voltage reference and input channel selections will
not go into effect until ADEN is set. The ADC does not consume power when ADEN is cleared, so it is recommended to
switch off the ADC before entering power saving sleep modes.
The ADC generates a 10-bit result which is presented in the ADC data registers, ADCH and ADCL. By default, the result is
presented right adjusted, but can optionally be presented left adjusted by setting the ADLAR bit in ADMUX.
If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must
be read first, then ADCH, to ensure that the content of the data registers belongs to the same conversion. Once ADCL is
read, ADC access to data registers is blocked. This means that if ADCL has been read, and a conversion completes before
ADCH is read, neither register is updated and the result from the conversion is lost. When ADCH is read, ADC access to the
ADCH and ADCL registers is re-enabled.
The ADC has its own interrupt which can be triggered when a conversion completes. When ADC access to the data registers
is prohibited between reading of ADCH and ADCL, the interrupt will trigger even if the result is lost.
23.4 Starting a Conversion
A single conversion is started by writing a logical one to the ADC start conversion bit, ADSC. This bit stays high as long as
the conversion is in progress and will be cleared by hardware when the conversion is completed. If a different data channel
is selected while a conversion is in progress, the ADC will finish the current conversion before performing the channel
change.
Alternatively, a conversion can be triggered automatically by various sources. Auto triggering is enabled by setting the ADC
auto trigger enable bit, ADATE in ADCSRA. The trigger source is selected by setting the ADC trigger select bits, ADTS in
ADCSRB (see description of the ADTS bits for a list of the trigger sources). When a positive edge occurs on the selected
trigger signal, the ADC prescaler is reset and a conversion is started. This provides a method of starting conversions at fixed
intervals. If the trigger signal still is set when the conversion completes, a new conversion will not be started. If another
positive edge occurs on the trigger signal during conversion, the edge will be ignored. Note that an interrupt flag will be set
even if the specific interrupt is disabled or the global interrupt enable bit in SREG is cleared.
A conversion can thus be triggered without causing an interrupt. However, the interrupt flag must be cleared in order to
trigger a new conversion at the next interrupt event.
Figure 23-2. ADC Auto Trigger Logic
ADTS[2:0]
Prescaler
START
CLKADC
ADIF
ADATE
SOURCE 1
.
.
.
.
Conversion
Logic
Edge
Detector
SOURCE n
ADSC
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Using the ADC interrupt flag as a trigger source makes the ADC start a new conversion as soon as the ongoing conversion
has finished. The ADC then operates in free running mode, constantly sampling and updating the ADC data register. The
first conversion must be started by writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform
successive conversions independently of whether the ADC interrupt flag, ADIF is cleared or not.
If auto triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to one. ADSC can also be used
to determine if a conversion is in progress. The ADSC bit will be read as one during a conversion, independently of how the
conversion was started.
23.5 Prescaling and Conversion Timing
Figure 23-3. ADC Prescaler
ADEN
Reset
START
7-Bit ADC Prescaler
CK
ADPS0
ADPS1
ADPS2
ADC Clock Source
By default, the successive approximation circuitry requires an input clock frequency between 50kHz and 200kHz to get
maximum resolution. If a lower resolution than 10 bits is needed, the input clock frequency to the ADC can be higher than
200kHz to get a higher sample rate.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency from any CPU frequency above
100kHz. The prescaling is set by the ADPS bits in ADCSRA. The prescaler starts counting from the moment the ADC is
switched on by setting the ADEN bit in ADCSRA. The prescaler keeps running for as long as the ADEN bit is set, and is
continuously reset when ADEN is low.
When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion starts at the following rising
edge of the ADC clock cycle. See Section 23.5.1 “Differential Gain Channels” on page 213 for details on differential
conversion timing.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched on (ADEN in ADCSRA is set)
takes 25 ADC clock cycles in order to initialize the analog circuitry.
When the bandgap reference voltage is used as input to the ADC, it will take a certain time for the voltage to stabilize. If not
stabilized, the first value read after the first conversion may be wrong.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 13.5 ADC clock
cycles after the start of a first conversion. When a conversion is complete, the result is written to the ADC data registers, and
ADIF is set. In single conversion mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new
conversion will be initiated on the first rising ADC clock edge.
When auto triggering is used, the prescaler is reset when the trigger event occurs. This assures a fixed delay from the trigger
event to the start of conversion. In this mode, the sample-and-hold takes place 2 ADC clock cycles after the rising edge on
the trigger source signal. Three additional CPU clock cycles are used for synchronization logic.
When using differential mode, along with auto trigging from a source other than the ADC conversion complete, each
conversion will require 25 ADC clocks. This is because the ADC must be disabled and re-enabled after every conversion.
In free running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains
high. For a summary of conversion times, see Table 23-1 on page 212.
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Figure 23-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Next
Conversion
First Conversion
Cycle Number
ADC Clock
ADEN
1
2
12
13
14
15
16
17
18
19
20
21
22
23
24
25
1
2
3
ADSC
ADIF
ADCH
MSB of Result
LSB of Result
ADCL
MUX and REFS
Update
Conversion
Complete
Sample and Hold
MUX and REFS
Update
Figure 23-5. ADC Timing Diagram, Single Conversion
One Conversion
Next Conversion
Cycle Number
ADC Clock
ADSC
1
2
3
4
5
6
7
8
9
10
11
12
13
1
2
3
ADIF
ADCH
MSB of Result
LSB of Result
ADCL
Sample and Hold
MUX and REFS
Update
Conversion
Complete
MUX and REFS
Update
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Figure 23-6. ADC Timing Diagram, Auto Triggered Conversion
One Conversion
Next Conversion
Cycle Number
ADC Clock
1
2
3
4
5
6
7
8
9
10
11
12
13
1
2
Trigger
Source
ADATE
ADIF
ADCH
ADCL
MSB of Result
LSB of Result
Prescaler
Reset
Sample and Hold
MUX and REFS
Update
Conversion
Complete
Prescaler
Reset
Figure 23-7. ADC Timing Diagram, Free Running Conversion
One Conversion
Next Conversion
Cycle Number
ADC Clock
ADSC
11
12
13
1
2
3
4
ADIF
ADCH
MSB of Result
LSB of Result
ADCL
Sample and Hold
MUX and REFS
Update
Conversion
Complete
Table 23-1. ADC Conversion Time
Sample and Hold (Cycles from
Start of Conversion)
Condition
Conversion Time (Cycles)
First conversion
14.5
1.5
25
13
Normal conversions, single ended
Auto triggered conversions
Normal conversions, differential
2
13.5
13/14
1.5/2.5
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23.5.1 Differential Gain Channels
When using differential gain channels, certain aspects of the conversion need to be taken into consideration. Note that the
differential channels should not be used with an AREF < 2V.
Differential conversions are synchronized to the internal clock CKADC2 equal to half the ADC clock. This synchronization is
done automatically by the ADC interface in such a way that the sample-and-hold occurs at a specific phase of CKADC2. A
conversion initiated by the user (i.e., all single conversions, and the first free running conversion) when CKADC2 is low will
take the same amount of time as a single ended conversion (13 ADC clock cycles from the next prescaled clock cycle). A
conversion initiated by the user when CKADC2 is high will take 14 ADC clock cycles due to the synchronization mechanism. In
free running mode, a new conversion is initiated immediately after the previous conversion completes, and since CKADC2 is
high at this time, all automatically started (i.e., all but the first) free running conversions will take 14 ADC clock cycles.
The gain stage is optimized for a bandwidth of 4kHz at all gain settings. Higher frequencies may be subjected to non-linear
amplification. An external low-pass filter should be used if the input signal contains higher frequency components than the
gain stage bandwidth. Note that the ADC clock frequency is independent of the gain stage bandwidth limitation. For
example, the ADC clock period may be 6µs, allowing a channel to be sampled at 12kSPS, regardless of the bandwidth of
this channel.
If differential gain channels are used and conversions are started by auto triggering, the ADC must be switched off between
conversions. When auto triggering is used, the ADC prescaler is reset before the conversion is started. Since the gain stage
is dependent of a stable ADC clock prior to the conversion, this conversion will not be valid. By disabling and then
re-enabling the ADC between each conversion (writing ADEN in ADCSRA to “0” then to “1”), only extended conversions are
performed. The result from the extended conversions will be valid. See Section 23.5 “Prescaling and Conversion Timing” on
page 210 for timing details.
23.6 Changing Channel or Reference Selection
The MUXn and REFS1:0 bits in the ADMUX register are single buffered through a temporary register to which the CPU has
random access. This ensures that the channels and reference selection only takes place at a safe point during the
conversion. The channel and reference selection is continuously updated until a conversion is started. Once the conversion
starts, the channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Continuous updating
resumes in the last ADC clock cycle before the conversion completes (ADIF in ADCSRA is set). Note that the conversion
starts on the following rising ADC clock edge after ADSC is written. The user is thus advised not to write new channel or
reference selection values to ADMUX until one ADC clock cycle after ADSC is written.
If auto triggering is used, the exact time of the triggering event can be indeterministic. Special care must be taken when
updating the ADMUX register, in order to control which conversion will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the ADMUX register is changed in this
period, the user cannot tell if the next conversion is based on the old or the new settings. ADMUX can be safely updated in
the following ways:
1. When ADATE or ADEN is cleared.
2. During conversion, minimum one ADC clock cycle after the trigger event.
3. After a conversion, before the interrupt flag used as trigger source is cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next ADC conversion.
Special care should be taken when changing differential channels. Once a differential channel has been selected, the gain
stage may take as much as 125µs to stabilize to the new value. Thus conversions should not be started within the first 125µs
after selecting a new differential channel. Alternatively, conversion results obtained within this period should be discarded.
The same settling time should be observed for the first differential conversion after changing ADC reference (by changing
the REFS1:0 bits in ADMUX).
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23.6.1 ADC Input Channels
When changing channel selections, the user should observe the following guidelines to ensure that the correct channel is
selected:
In single conversion mode, always select the channel before starting the conversion. The channel selection may be changed
one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the conversion to complete
before changing the channel selection.
In free running mode, always select the channel before starting the first conversion. The channel selection may be changed
one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the first conversion to complete,
and then change the channel selection. Since the next conversion has already started automatically, the next result will
reflect the previous channel selection. Subsequent conversions will reflect the new channel selection.
When switching to a differential gain channel, the first conversion result may have a poor accuracy due to the required
settling time for the automatic offset cancellation circuitry. The user should preferably disregard the first conversion result.
23.6.2 ADC Voltage Reference
The reference voltage for the ADC (VREF) indicates the conversion range for the ADC. Single ended channels that exceed
VREF will result in codes close to 0x3FF. VREF can be selected as either AVCC, internal 2.56V reference, or external AREF
pin.
AVCC is connected to the ADC through a passive switch. The internal 2.56V reference is generated from the internal
bandgap reference (VBG) through an internal amplifier. In either case, the external AREF pin is directly connected to the
ADC, and the reference voltage can be made more immune to noise by connecting a capacitor between the AREF pin and
ground. VREF can also be measured at the AREF pin with a high impedant voltmeter. Note that VREF is a high impedant
source, and only a capacitive load should be connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use the other reference voltage options
in the application, as they will be shorted to the external voltage. If no external voltage is applied to the AREF pin, the user
may switch between AVCC and 2.56V as reference selection. The first ADC conversion result after switching reference
voltage source may be inaccurate, and the user is advised to discard this result.
If differential channels are used, the selected reference should not be closer to AVCC than indicated in
Table 28-10 on page 295.
23.7 ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise induced from the CPU core
and other I/O peripherals. The noise canceler can be used with ADC noise reduction and idle mode. To make use of this
feature, the following procedure should be used:
1. Make sure that the ADC is enabled and is not busy converting. Single conversion mode must be selected and the
ADC conversion complete interrupt must be enabled.
2. Enter ADC noise reduction mode (or Idle mode). The ADC will start a conversion once the CPU has been halted.
3. If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and
execute the ADC Conversion Complete interrupt routine. If another interrupt wakes up the CPU before the ADC
conversion is complete, that interrupt will be executed, and an ADC Conversion Complete interrupt request will be
generated when the ADC conversion completes. The CPU will remain in active mode until a new sleep command
is executed.
Note that the ADC will not be automatically turned off when entering other sleep modes than Idle mode and ADC noise
reduction mode. The user is advised to write zero to ADEN before entering such sleep modes to avoid excessive power
consumption. If the ADC is enabled in such sleep modes and the user wants to perform differential conversions, the user is
advised to switch the ADC off and on after waking up from sleep to prompt an extended conversion to get a valid result.
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23.7.1 Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 23-8 An analog source applied to ADCn is
subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is selected as input for the
ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance (combined
resistance in the input path).
The ADC is optimized for analog signals with an output impedance of approximately 10kΩ or less. If such a source is used,
the sampling time will be negligible. If a source with higher impedance is used, the sampling time will depend on how long
time the source needs to charge the S/H capacitor, with can vary widely. The user is recommended to only use low impedant
sources with slowly varying signals, since this minimizes the required charge transfer to the S/H capacitor.
If differential gain channels are used, the input circuitry looks somewhat different, although source impedances of a few
hundred kΩ or less is recommended.
Signal components higher than the nyquist frequency (fADC/2) should not be present for either kind of channels, to avoid
distortion from unpredictable signal convolution. The user is advised to remove high frequency components with a low-pass
filter before applying the signals as inputs to the ADC.
Figure 23-8. Analog Input Circuitry
IIH
ADCn
1 to 100kΩ
IIL
CS/H = 14pF
VCC/2
23.7.2 Analog Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of analog measurements. If
conversion accuracy is critical, the noise level can be reduced by applying the following techniques:
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1. Keep analog signal paths as short as possible. Make sure analog tracks run over the analog ground plane,
and keep them well away from high-speed switching digital tracks.
2. The AVCC pin on the device should be connected to the digital VCC supply voltage via an LC network as
shown in Figure 23-9.
3. Use the ADC noise canceler function to reduce induced noise from the CPU.
4. If any ADC port pins are used as digital outputs, it is essential that these do not switch while a conversion is
in progress.
Figure 23-9. ADC Power Connections
PA4 (ADC4)
PA5 (ADC5)
PA6 (ADC6)
PA7 (ADC7)
AREF
GND
AVCC
PC7
23.7.3 Offset Compensation Schemes
The gain stage has a built-in offset cancellation circuitry that nulls the offset of differential measurements as much as
possible. The remaining offset in the analog path can be measured directly by selecting the same channel for both
differential inputs. This offset residue can be then subtracted in software from the measurement results. Using this kind of
software based offset correction, offset on any channel can be reduced below one LSB.
23.7.4 ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n steps (LSBs). The lowest code is read
as 0, and the highest code is read as 2n-1.
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Several parameters describe the deviation from the ideal behavior:
●
Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition (at 0.5 LSB). Ideal value:
0 LSB.
Figure 23-10. Offset Error
Output Code
Ideal ADC
Actual ADC
Offset
Error
V
Input Voltage
REF
●
Gain error: After adjusting for offset, the gain error is found as the deviation of the last transition (0x3FE to 0x3FF)
compared to the ideal transition (at 1.5 LSB below maximum). Ideal value: 0 LSB
Figure 23-11. Gain Error
Output Code
Gain
Error
Ideal ADC
Actual ADC
V
Input Voltage
REF
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●
Integral non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum deviation of an actual
transition compared to an ideal transition for any code. Ideal value: 0 LSB.
Figure 23-12. Integral Non-linearity (INL)
Output Code
Ideal ADC
Actual ADC
V
Input Voltage
REF
●
Differential non-linearity (DNL): The maximum deviation of the actual code width (the interval between two adjacent
transitions) from the ideal code width (1 LSB). Ideal value: 0 LSB.
Figure 23-13. Differential Non-linearity (DNL)
Output Code
0x3FF
1 LSB
DNL
0x000
0
V
Input Voltage
REF
●
●
Quantization error: Due to the quantization of the input voltage into a finite number of codes, a range of input voltages
(1 LSB wide) will code to the same value. Always ±0.5 LSB.
Absolute accuracy: The maximum deviation of an actual (unadjusted) transition compared to an ideal transition for
any code. This is the compound effect of offset, gain error, differential error, non-linearity, and quantization error. ideal
value: ±0.5 LSB.
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23.8 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC result registers (ADCL,
ADCH).
For single ended conversion, the result is
V
1024
IN
------------------------
ADC =
V
REF
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 23-3 on page 220 and
Table 23-4 on page 221). 0x000 represents analog ground, and 0x3FF represents the selected reference voltage minus one
LSB.
If differential channels are used, the result is
(V
– V
) GAIN 512
NEG
POS
-----------------------------------------------------------------------
ADC =
V
REF
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin, GAIN the selected gain factor,
and VREF the selected voltage reference. The result is presented in two’s complement form, from 0x200 (-512d) through
0x1FF (+511d). Note that if the user wants to perform a quick polarity check of the results, it is sufficient to read the MSB of
the result (ADC9 in ADCH). If this bit is one, the result is negative, and if this bit is zero, the result is positive. Figure 23-14
shows the decoding of the differential input range.
Table 23-2 on page 220 shows the resulting output codes if the differential input channel pair (ADCn - ADCm) is selected
with a gain of GAIN and a reference voltage of VREF
.
Figure 23-14. Differential Measurement Range
Output Code
0x1FF
0x000
0x3FF
0
V
/Gain
V
/Gain Differential Input
Voltage (Volts)
REF
REF
0x200
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Table 23-2. Correlation between Input Voltage and Output Codes
VADCn
Read code
0x1FF
0x1FF
0x1FE
...
Corresponding Decimal Value
VADCm + VREF/GAIN
VADCm + 0.999 VREF/GAIN
VADCm + 0.998 VREF/GAIN
...
511
511
510
...
VADCm + 0.001 VREF/GAIN
VADCm
0x001
0x000
0x3FF
...
1
0
VADCm – 0.001 VREF/GAIN
...
-1
...
VADCm – 0.999 VREF/GAIN
VADCm – VREF/GAIN
0x201
0x200
–511
–512
Example:
ADMUX = 0xED (ADC3 - ADC2, 10x gain, 2.56V reference, left adjusted result)
Voltage on ADC3 is 300mV, voltage on ADC2 is 500mV.
ADCR = 512 × 10 × (300 – 500) / 2560 = –400 = 0x270
ADCL will thus read 0x00, and ADCH will read 0x9C. Writing zero to ADLAR right adjusts the result: ADCL =
0x70, ADCH = 0x02.
23.9 Register Description
23.9.1 ADMUX – ADC Multiplexer Selection Register
Bit
7
REFS1
R/W
0
6
REFS0
R/W
0
5
ADLAR
R/W
0
4
MUX4
R/W
0
3
MUX3
R/W
0
2
MUX2
R/W
0
1
MUX1
R/W
0
0
MUX0
R/W
0
(0x7C)
ADMUX
Read/Write
Initial Value
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 23-3. If these bits are changed during a conversion,
the change will not go in effect until this conversion is complete (ADIF in ADCSRA is set). The internal voltage reference
options may not be used if an external reference voltage is being applied to the AREF pin.
Table 23-3. Voltage Reference Selections for ADC
REFS1
REFS0
Voltage Reference Selection
0
0
1
1
0
1
0
1
AREF, Internal VREF turned off
AVCC with external capacitor at AREF pin
Internal 1.1V voltage reference with external capacitor at AREF pin
Internal 2.56V voltage reference with external capacitor at AREF pin
Note:
If differential channels are selected, only 2.56V should be used as internal voltage reference.
• Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC data register. Write one to ADLAR to left
adjust the result. Otherwise, the result is right adjusted. Changing the ADLAR bit will affect the ADC data register
immediately, regardless of any ongoing conversions. For a complete description of this bit, see Section 23.9.3 “ADCL and
ADCH – The ADC Data Register” on page 223.
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• Bits 4:0 – MUX4:0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the ADC. These bits also select the gain
for the differential channels. See Table 23-4 on page 221 for details. If these bits are changed during a conversion, the
change will not go in effect until this conversion is complete (ADIF in ADCSRA is set).
Table 23-4. Input Channel and Gain Selections
MUX4..0
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111
Single Ended Input
ADC0
Positive Differential Input
Negative Differential Input
Gain
ADC1
ADC2
ADC3
N/A
ADC4
ADC5
ADC6
ADC7
ADC0
ADC1
ADC0
ADC1
ADC2
ADC3
ADC2
ADC3
ADC0
ADC1
ADC2
ADC3
ADC4
ADC5
ADC6
ADC7
ADC0
ADC1
ADC2
ADC3
ADC4
ADC5
ADC0
ADC0
ADC0
ADC0
ADC2
ADC2
ADC2
ADC2
ADC1
ADC1
ADC1
ADC1
ADC1
ADC1
ADC1
ADC1
ADC2
ADC2
ADC2
ADC2
ADC2
ADC2
10x
10x
200x
200x
10x
10x
200x
200x
1x
1x
1x
N/A
1x
1x
1x
1x
1x
1x
1x
1x
1x
1x
1x
1.1V (VBG
)
N/A
0 V (GND)
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23.9.2 ADCSRA – ADC Control and Status Register A
Bit
7
ADEN
R/W
0
6
ADSC
R/W
0
5
ADATE
R/W
0
4
ADIF
R/W
0
3
ADIE
R/W
0
2
ADPS2
R/W
0
1
ADPS1
R/W
0
0
ADPS0
R/W
0
(0x7A)
ADCSRA
Read/Write
Initial Value
• Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the ADC off while a conversion is
in progress, will terminate this conversion.
• Bit 6 – ADSC: ADC Start Conversion
In single conversion mode, write this bit to one to start each conversion. In free running mode, write this bit to one to start the
first conversion. The first conversion after ADSC has been written after the ADC has been enabled, or if ADSC is written at
the same time as the ADC is enabled, will take 25 ADC clock cycles instead of the normal 13. This first conversion performs
initialization of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is complete, it returns to zero. Writing
zero to this bit has no effect.
• Bit 5 – ADATE: ADC Auto Trigger Enable
When this bit is written to one, auto triggering of the ADC is enabled. The ADC will start a conversion on a positive edge of
the selected trigger signal. The trigger source is selected by setting the ADC trigger select bits, ADTS in ADCSRB.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is set when an ADC conversion completes and the data registers are updated. The ADC conversion complete
interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, ADIF is cleared by writing a logical one to the flag. Beware that if
doing a read-modify-write on ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions
are used.
• Bit 3 – ADIE: ADC Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the ADC conversion complete interrupt is activated.
• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the XTAL frequency and the input clock to the ADC.
Table 23-5. ADC Prescaler Selections
ADPS2
ADPS1
ADPS0
Division Factor
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
2
2
4
8
16
32
64
128
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23.9.3 ADCL and ADCH – The ADC Data Register
23.9.3.1 ADLAR = 0
Bit
15
14
13
12
11
10
9
8
(0x79)
(0x78)
–
–
–
–
–
–
ADC9
ADC8
ADCH
ADCL
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
7
R
R
0
6
R
R
0
5
R
R
0
4
R
R
0
3
R
R
0
2
R
R
0
1
R
R
0
0
R
R
0
Read/Write
Initial Value
0
0
0
0
0
0
0
0
23.9.3.2 ADLAR = 1
Bit
15
14
13
12
11
10
9
8
(0x79)
(0x78)
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
ADCL
ADC1
ADC0
–
5
–
4
–
3
–
2
–
1
–
0
7
R
R
0
6
R
R
0
Read/Write
Initial Value
R
R
0
R
R
0
R
R
0
R
R
0
R
R
0
R
R
0
0
0
0
0
0
0
0
0
When an ADC conversion is complete, the result is found in these two registers. If differential channels are used, the result is
presented in two’s complement form.
When ADCL is read, the ADC data register is not updated until ADCH is read. Consequently, if the result is left adjusted and
no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from the registers. If ADLAR is set,
the result is left adjusted. If ADLAR is cleared (default), the result is right adjusted.
• ADC9:0: ADC Conversion Result
These bits represent the result from the conversion, as detailed in Section 23.8 “ADC Conversion Result” on page 219.
23.9.4 ADCSRB – ADC Control and Status Register B
Bit
7
–
6
ACME
R/W
0
5
–
4
–
3
–
2
ADTS2
R/W
0
1
ADTS1
R/W
0
0
ADTS0
R/W
0
(0x7B)
ADCSRB
Read/Write
Initial Value
R
0
R
0
R
0
R
0
• Bit 7, 5:3 – Reserved
These bits are reserved for future use in the Atmel® ATmega164P-B/324P-B/644P-B. For ensuring culpability with future
devices, these bits must be written zero when ADCSRB is written.
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• Bit 2:0 – ADTS2:0: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger an ADC conversion. If ADATE
is cleared, the ADTS[2:0] settings will have no effect. A conversion will be triggered by the rising edge of the selected
interrupt flag. Note that switching from a trigger source that is cleared to a trigger source that is set, will generate a positive
edge on the trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to free running mode
(ADTS[2:0]=0) will not cause a trigger event, even if the ADC interrupt flag is set.
Table 23-6. ADC Auto Trigger Source Selections
ADTS2
ADTS1
ADTS0
Trigger Source
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Free running mode
Analog comparator
External interrupt request 0
Timer/Counter0 compare match
Timer/Counter0 overflow
Timer/Counter1 compare match B
Timer/Counter1 overflow
Timer/Counter1 capture event
23.9.5 DIDR0 – Digital Input Disable Register 0
Bit
7
ADC7D
R/W
0
6
ADC6D
R/W
0
5
ADC5D
R/W
0
4
ADC4D
R/W
0
3
ADC3D
R/W
0
2
ADC2D
R/W
0
1
ADC1D
R/W
0
0
ADC0D
R/W
0
(0x7E)
DIDR0
Read/Write
Initial Value
• Bit 7:0 – ADC7D..ADC0D: ADC7:0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN
register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC7:0 pin and the digital
input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer.
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24. JTAG Interface and On-chip Debug System
24.1 Features
●
●
●
JTAG (IEEE std. 1149.1 compliant) interface
Boundary-scan capabilities according to the IEEE std. 1149.1 (JTAG) standard
Debugger access to:
●
●
●
●
●
All internal peripheral units
Internal and external RAM
The internal register file
Program counter
EEPROM and flash memories
●
Extensive on-chip debug support for break conditions, including
●
●
●
●
●
AVR® break instruction
Break on change of program memory flow
Single step break
Program memory break points on single address or address range
Data memory break points on single address or address range
●
●
Programming of flash, EEPROM, fuses, and lock bits through the JTAG interface
On-chip debugging supported by AVR Studio®
24.2 Overview
The AVR IEEE std. 1149.1 compliant JTAG interface can be used for
●
●
●
Testing PCBs by using the JTAG Boundary-scan capability
Programming the non-volatile memories, Fuses and Lock bits
On-chip debugging
A brief description is given in the following sections. Detailed descriptions for programming via the JTAG interface, and using
the boundary-scan chain can be found in the sections Section 27.10 “Programming via the JTAG Interface” on page 274 and
Section 25. “IEEE 1149.1 (JTAG) Boundary-scan” on page 231, respectively. The on-chip debug support is considered being
private JTAG instructions, and distributed within ATMEL and to selected third party vendors only.
Figure 24-1 on page 226 shows a block diagram of the JTAG interface and the on-chip debug system. The TAP controller is
a state machine controlled by the TCK and TMS signals. The TAP controller selects either the JTAG instruction register or
one of several data registers as the scan chain (shift register) between the TDI – input and TDO – output. The instruction
register holds JTAG instructions controlling the behavior of a data register.
The ID-register, bypass register, and the boundary-scan chain are the data registers used for board-level testing. The JTAG
programming interface (actually consisting of several physical and virtual data registers) is used for serial programming via
the JTAG interface. The internal scan chain and break point scan chain are used for on-chip debugging only.
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24.3 TAP – Test Access Port
The JTAG interface is accessed through four of the AVR® pins. In JTAG terminology, these pins constitute the test access
port – TAP. These pins are:
●
●
●
●
TMS: Test mode select. This pin is used for navigating through the TAP-controller state machine.
TCK: Test clock. JTAG operation is synchronous to TCK.
TDI: Test data in. Serial input data to be shifted in to the instruction register or data register (scan chains).
TDO: Test data out. Serial output data from instruction register or data register.
The IEEE std. 1149.1 also specifies an optional TAP signal; TRST – Test ReSeT – which is not provided.
When the JTAGEN fuse is unprogrammed, these four TAP pins are normal port pins, and the TAP controller is in reset.
When programmed, the input TAP signals are internally pulled high and the JTAG is enabled for boundary-scan and
programming. The device is shipped with this fuse programmed.
For the on-chip debug system, in addition to the JTAG interface pins, the RESET pin is monitored by the debugger to be able
to detect external reset sources. The debugger can also pull the RESET pin low to reset the whole system, assuming only
open collectors on the reset line are used in the application.
Figure 24-1. Block Diagram
I/O PORT 0
Device Boundary
Boundary Scan Chain
TDI
TDO
TCK
TMS
JTAG Programming
Interface
Tap
Controller
AVR CPU
Internal
Scan
Chain
Flash
Address
Data
PC
Instruction
Register
Memory
Instruction
ID
Register
Breakpoint
Unit
Flow Control
Unit
M
U
X
Bypass
Register
Digital
Perpheral
Units
Analog
Peripheral
Units
Analog
inputs
Breakpoint
Scan Chain
JTAG/ AVR Core
Communication
Interface
Address
Decoder
OCD Status
and Control
Control and
Clock lines
I/O PORT n
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Figure 24-2. TAP Controller State Diagram
1
Test Logic Reset
0
1
1
1
0
Run Test/Idle
Select DR Scan
0
Select IR Scan
0
1
1
Capture DR
0
Capture IR
0
Shift DR
1
0
Shift IR
1
0
1
1
Exit1 DR
0
Exit1 IR
0
Pause DR
1
0
Pause IR
1
0
0
0
Exit2 DR
1
Exit2 IR
1
Update DR
Update IR
1
0
1
0
24.4 TAP Controller
The TAP controller is a 16-state finite state machine that controls the operation of the boundary-scan circuitry, JTAG
programming circuitry, or on-chip debug system. The state transitions depicted in Figure 24-2 depend on the signal present
on TMS (shown adjacent to each state transition) at the time of the rising edge at TCK. The initial state after a power-on
reset is test-logic-reset.
As a definition in this document, the LSB is shifted in and out first for all shift registers.
Assuming run-test/Idle is the present state, a typical scenario for using the JTAG interface is:
●
At the TMS input, apply the sequence 1, 1, 0, 0 at the rising edges of TCK to enter the shift instruction register – shift-
IR state. While in this state, shift the four bits of the JTAG instructions into the JTAG Instruction register from the TDI
input at the rising edge of TCK. The TMS input must be held low during input of the 3LSBs in order to remain in the
shift-IR state. The MSB of the instruction is shifted in when this state is left by setting TMS high. While the instruction
is shifted in from the TDI pin, the captured IR-state 0x01 is shifted out on the TDO pin. The JTAG instruction selects a
particular data register as path between TDI and TDO and controls the circuitry surrounding the selected data
register.
●
Apply the TMS sequence 1, 1, 0 to re-enter the run-test/idle state. The instruction is latched onto the parallel output
from the shift register path in the update-IR state. The exit-IR, pause-IR, and exit2-IR states are only used for
navigating the state machine.
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●
●
At the TMS input, apply the sequence 1, 0, 0 at the rising edges of TCK to enter the shift data register – shift-DR state.
While in this state, upload the selected data register (selected by the present JTAG instruction in the JTAG instruction
register) from the TDI input at the rising edge of TCK. In order to remain in the shift-DR state, the TMS input must be
held low during input of all bits except the MSB. The MSB of the data is shifted in when this state is left by setting TMS
high. While the data register is shifted in from the TDI pin, the parallel inputs to the data register captured in the
capture-DR state is shifted out on the TDO pin.
Apply the TMS sequence 1, 1, 0 to re-enter the run-test/idle state. If the selected data register has a latched
parallel-output, the latching takes place in the update-DR state. The exit-DR, pause-DR, and exit2-DR states are only
used for navigating the state machine.
As shown in the state diagram, the run-test/idle state need not be entered between selecting JTAG instruction and using
data registers, and some JTAG instructions may select certain functions to be performed in the run-test/idle, making it
unsuitable as an idle state.
Note:
Independent of the initial state of the TAP controller, the test-logic-reset state can always be entered by holding
TMS high for five TCK clock periods.
For detailed information on the JTAG specification, refer to the literature listed in Section 24.9 “Bibliography” on page 229.
24.5 Using the Boundary-scan Chain
A complete description of the boundary-scan capabilities are given in the section Section 25. “IEEE 1149.1 (JTAG)
Boundary-scan” on page 231.
24.6 Using the On-chip Debug System
As shown in Figure 24-1 on page 226, the hardware support for on-chip debugging consists mainly of
●
●
●
A scan chain on the interface between the internal AVR® CPU and the internal peripheral units.
Break point unit.
Communication interface between the CPU and JTAG system.
All read or modify/write operations needed for implementing the debugger are done by applying AVR instructions via the
internal AVR CPU scan chain. The CPU sends the result to an I/O memory mapped location which is part of the
communication interface between the CPU and the JTAG system.
The break point unit implements break on change of program flow, single step break, two program memory break points,
and two combined break points. together, the four break points can be configured as either:
●
●
●
●
●
4 single program memory break points.
3 single program memory break point + 1 single data memory break point.
2 single program memory break points + 2 single data memory break points.
2 single program memory break points + 1 program memory break point with mask (“range break point”).
2 single program memory break points + 1 data memory break point with mask (“range break point”).
A debugger, like the AVR Studio®, may however use one or more of these resources for its internal purpose, leaving less
flexibility to the end-user.
A list of the on-chip debug specific JTAG instructions is given in Section 24.7 “On-chip Debug Specific JTAG Instructions” on
page 229.
The JTAGEN fuse must be programmed to enable the JTAG test access port. In addition, the OCDEN fuse must be
programmed and no lock bits must be set for the on-chip debug system to work. As a security feature, the on-chip debug
system is disabled when either of the LB1 or LB2 lock bits are set. Otherwise, the on-chip debug system would have
provided a back-door into a secured device.
The AVR Studio enables the user to fully control execution of programs on an AVR device with on-chip debug capability,
AVR in-circuit emulator, or the built-in AVR instruction set simulator. AVR Studio supports source level execution of
assembly programs assembled with Atmel Corporation AVR Assembler and C programs compiled with third party vendors’
compilers.
AVR Studio runs under Microsoft Windows® 95/98/2000 and Microsoft Windows NT®.
For a full description of the AVR Studio, please refer to the AVR Studio user guide. Only highlights are presented in this
document.
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All necessary execution commands are available in AVR Studio®, both on source level and on disassembly level. The user
can execute the program, single step through the code either by tracing into or stepping over functions, step out of functions,
place the cursor on a statement and execute until the statement is reached, stop the execution, and reset the execution
target. In addition, the user can have an unlimited number of code break points (using the BREAK instruction) and up to two
data memory break points, alternatively combined as a mask (range) break point.
24.7 On-chip Debug Specific JTAG Instructions
The on-chip debug support is considered being private JTAG instructions, and distributed within Atmel® and to selected third
party vendors only. Instruction opcodes are listed for reference.
24.7.1 PRIVATE0; 0x8
Private JTAG instruction for accessing on-chip debug system.
24.7.2 PRIVATE1; 0x9
Private JTAG instruction for accessing on-chip debug system.
24.7.3 PRIVATE2; 0xA
Private JTAG instruction for accessing on-chip debug system.
24.7.4 PRIVATE3; 0xB
Private JTAG instruction for accessing on-chip debug system.
24.8 Using the JTAG Programming Capabilities
Programming of AVR® parts via JTAG is performed via the 4-pin JTAG port, TCK, TMS, TDI, and TDO. These are the only
pins that need to be controlled/observed to perform JTAG programming (in addition to power pins). It is not required to apply
12V externally. The JTAGEN fuse must be programmed and the JTD bit in the MCUCR register must be cleared to enable
the JTAG test access port.
The JTAG programming capability supports:
●
●
●
●
Flash programming and verifying.
EEPROM programming and verifying.
Fuse programming and verifying.
Lock bit programming and verifying.
The lock bit security is exactly as in parallel programming mode. If the lock bits LB1 or LB2 are programmed, the OCDEN
fuse cannot be programmed unless first doing a chip erase. This is a security feature that ensures no back-door exists for
reading out the content of a secured device.
The details on programming through the JTAG interface and programming specific JTAG instructions are given in the
section Section 27.10 “Programming via the JTAG Interface” on page 274.
24.9 Bibliography
For more information about general boundary-scan, the following literature can be consulted:
●
●
IEEE: IEEE Std. 1149.1-1990. IEEE standard test access port and boundary-scan architecture, IEEE, 1993.
Colin maunder: The board designers guide to testable logic circuits, addison-wesley, 1992.
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24.10 Register Description
24.10.1 OCDR – On-chip Debug Register
Bit
7
MSB/IDRD
R/W
6
5
4
3
2
1
0
0x31 (0x51)
Read/Write
Initial Value
LSB
R/W
0
OCDR
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
The OCDR register provides a communication channel from the running program in the microcontroller to the debugger. The
CPU can transfer a byte to the debugger by writing to this location. At the same time, an internal flag; I/O debug register dirty
– IDRD – is set to indicate to the debugger that the register has been written. When the CPU reads the OCDR register the 7
LSB will be from the OCDR register, while the MSB is the IDRD bit. The debugger clears the IDRD bit when it has read the
information.
In some AVR® devices, this register is shared with a standard I/O location. In this case, the OCDR register can only be
accessed if the OCDEN fuse is programmed, and the debugger enables access to the OCDR register. In all other cases, the
standard I/O location is accessed.
Refer to the debugger documentation for further information on how to use this register.
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25. IEEE 1149.1 (JTAG) Boundary-scan
25.1 Features
●
●
●
●
●
JTAG (IEEE std. 1149.1 compliant) interface
Boundary-scan capabilities according to the JTAG standard
Full scan of all port functions as well as analog circuitry having off-chip connections
Supports the optional IDCODE instruction
Additional public AVR_RESET instruction to reset the AVR
25.2 Overview
The boundary-scan chain has the capability of driving and observing the logic levels on the digital I/O pins, as well as the
boundary between digital and analog logic for analog circuitry having off-chip connections. At system level, all ICs having
JTAG capabilities are connected serially by the TDI/TDO signals to form a long shift register. An external controller sets up
the devices to drive values at their output pins, and observe the input values received from other devices. The controller
compares the received data with the expected result. In this way, boundary-scan provides a mechanism for testing
interconnections and integrity of components on printed circuits boards by using the four TAP signals only.
The four IEEE 1149.1 defined mandatory JTAG instructions IDCODE, BYPASS, SAMPLE/PRELOAD, and EXTEST, as well
as the AVR® specific public JTAG instruction AVR_RESET can be used for testing the printed circuit board. Initial scanning
of the data register path will show the ID-code of the device, since IDCODE is the default JTAG instruction. It may be
desirable to have the AVR device in reset during test mode. If not reset, inputs to the device may be determined by the scan
operations, and the internal software may be in an undetermined state when exiting the test mode. Entering reset, the
outputs of any port pin will instantly enter the high impedance state, making the HIGHZ instruction redundant. If needed, the
BYPASS instruction can be issued to make the shortest possible scan chain through the device. The device can be set in the
reset state either by pulling the external RESET pin low, or issuing the AVR_RESET instruction with appropriate setting of
the reset data register.
The EXTEST instruction is used for sampling external pins and loading output pins with data. The data from the output latch
will be driven out on the pins as soon as the EXTEST instruction is loaded into the JTAG IR-register. Therefore, the
SAMPLE/PRELOAD should also be used for setting initial values to the scan ring, to avoid damaging the board when issuing
the EXTEST instruction for the first time. SAMPLE/PRELOAD can also be used for taking a snapshot of the external pins
during normal operation of the part.
The JTAGEN fuse must be programmed and the JTD bit in the I/O register MCUCR must be cleared to enable the JTAG test
access port.
When using the JTAG interface for boundary-scan, using a JTAG TCK clock frequency higher than the internal chip
frequency is possible. The chip clock is not required to run.
25.3 Data Registers
The data registers relevant for boundary-scan operations are:
●
●
●
●
Bypass register
Device identification register
Reset register
Boundary-scan chain
25.3.1 Bypass Register
The bypass register consists of a single shift register stage. When the bypass register is selected as path between TDI and
TDO, the register is reset to 0 when leaving the capture-DR controller state. The bypass register can be used to shorten the
scan chain on a system when the other devices are to be tested.
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25.3.2 Device Identification Register
Figure 25-1 shows the structure of the device identification register.
Figure 25-1. The Format of the Device Identification Register
MSB
LSB
0
Bit
31
Version
4 bits
28
27
12
11
1
Device ID
Part Number
Manufacturer ID
1
16 bits
11 bits
1-bit
25.3.2.1 Version
Version is a 4-bit number identifying the revision of the component. The JTAG version number follows the revision of the
device. Revision A is 0x0, revision B is 0x1 and so on.
25.3.2.2 Part Number
The part number is a 16-bit code identifying the component. The JTAG part number for Atmel®
ATmega164P-B/324P-B/644P-B is listed in Table 27-6 on page 258.
25.3.2.3 Manufacturer ID
The manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufacturer ID for ATMEL is listed in
Table 27-6 on page 258.
25.3.3 Reset Register
The reset register is a test data register used to reset the part. Since the AVR tri-states port pins when reset, the reset
register can also replace the function of the unimplemented optional JTAG instruction HIGHZ.
A high value in the reset register corresponds to pulling the external reset low. The part is reset as long as there is a high
value present in the reset register. Depending on the fuse settings for the clock options, the part will remain reset for a reset
time-out period (refer to Section 9.2 “Clock Sources” on page 24) after releasing the reset register. The output from this data
register is not latched, so the reset will take place immediately, as shown in Figure 25-2 on page 232.
Figure 25-2. Reset Register
To
TDO
From Other internal and
external Reset Sources
From
TDI
Internal Reset
D
Q
Clock DR · AVR_RESET
25.3.4 Boundary-scan Chain
The boundary-scan chain has the capability of driving and observing the logic levels on the digital I/O pins, as well as the
boundary between digital and analog logic for analog circuitry having off-chip connections.
See Section 25.5 “Boundary-scan Chain” on page 234 for a complete description.
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25.4 Boundary-scan Specific JTAG Instructions
The instruction register is 4-bit wide, supporting up to 16 instructions. Listed below are the JTAG instructions useful for
Boundary-scan operation. Note that the optional HIGHZ instruction is not implemented, but all outputs with tri-state capability
can be set in high-impedant state by using the AVR_RESET instruction, since the initial state for all port pins is tri-state.
As a definition in this datasheet, the LSB is shifted in and out first for all shift registers.
The OPCODE for each instruction is shown behind the instruction name in hex format. The text describes which data
register is selected as path between TDI and TDO for each instruction.
25.4.1 EXTEST; 0x0
Mandatory JTAG instruction for selecting the boundary-scan chain as data register for testing circuitry external to the AVR®
package. For port-pins, pull-up disable, output control, output data, and input data are all accessible in the scan chain. For
analog circuits having off-chip connections, the interface between the analog and the digital logic is in the scan chain. The
contents of the latched outputs of the boundary-scan chain is driven out as soon as the JTAG IR-register is loaded with the
EXTEST instruction.
The active states are:
●
●
●
Capture-DR: Data on the external pins are sampled into the boundary-scan chain.
Shift-DR: The internal scan chain is shifted by the TCK input.
Update-DR: Data from the scan chain is applied to output pins.
25.4.2 IDCODE; 0x1
Optional JTAG instruction selecting the 32 bit ID-register as data register. The ID-register consists of a version number, a
device number and the manufacturer code chosen by JEDEC. This is the default instruction after power-up.
The active states are:
●
●
Capture-DR: Data in the IDCODE register is sampled into the boundary-scan chain.
Shift-DR: The IDCODE scan chain is shifted by the TCK input.
25.4.3 SAMPLE_PRELOAD; 0x2
Mandatory JTAG instruction for pre-loading the output latches and taking a snap-shot of the input/output pins without
affecting the system operation. However, the output latches are not connected to the pins. The boundary-scan chain is
selected as data register.
The active states are:
●
●
●
Capture-DR: Data on the external pins are sampled into the boundary-scan chain.
Shift-DR: The boundary-scan chain is shifted by the TCK input.
Update-DR: Data from the boundary-scan chain is applied to the output latches. However, the output latches are not
connected to the pins.
25.4.4 AVR_RESET; 0xC
The AVR specific public JTAG instruction for forcing the AVR device into the reset mode or releasing the JTAG reset source.
The TAP controller is not reset by this instruction. The one bit reset register is selected as data register. Note that the reset
will be active as long as there is a logic “one” in the reset chain. The output from this chain is not latched.
The active states are:
●
Shift-DR: The reset register is shifted by the TCK input.
25.4.5 BYPASS; 0xF
Mandatory JTAG instruction selecting the bypass register for data register.
The active states are:
●
●
Capture-DR: Loads a logic “0” into the bypass register.
Shift-DR: The bypass register cell between TDI and TDO is shifted.
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25.5 Boundary-scan Chain
The boundary-scan chain has the capability of driving and observing the logic levels on the digital I/O pins, as well as the
boundary between digital and analog logic for analog circuitry having off-chip connection.
25.5.1 Scanning the Digital Port Pins
Figure 25-3 on page 235 shows the boundary-scan cell for a bi-directional port pin. The pull-up function is disabled during
boundary-scan when the JTAG IC contains EXTEST or SAMPLE_PRELOAD. The cell consists of a bi-directional pin cell
that combines the three signals output control - OCxn, output data - ODxn, and input data - IDxn, into only a two-stage shift
register. The port and pin indexes are not used in the following description
The boundary-scan logic is not included in the figures in the datasheet. Figure 25-4 on page 236 shows a simple digital port
pin as described in the Section 14. “I/O-Ports” on page 57. The boundary-scan details from Figure 25-3 on page 235
replaces the dashed box in Figure 25-4 on page 236.
When no alternate port function is present, the input data - ID - corresponds to the PINxn register value (but ID has no
synchronizer), output data corresponds to the PORT register, output control corresponds to the data direction - DD register,
and the pull-up enable - PUExn - corresponds to logic expression PUD · DDxn · PORTxn.
Digital alternate port functions are connected outside the dotted box in Figure 25-4 on page 236 to make the scan chain read
the actual pin value. For analog function, there is a direct connection from the external pin to the analog circuit. There is no
scan chain on the interface between the digital and the analog circuitry, but some digital control signal to analog circuitry are
turned off to avoid driving contention on the pads.
When JTAG IR contains EXTEST or SAMPLE_PRELOAD the clock is not sent out on the port pins even if the CKOUT fuse
is programmed. Even though the clock is output when the JTAG IR contains SAMPLE_PRELOAD, the clock is not sampled
by the boundary scan.
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Figure 25-3. Boundary-scan Cell for Bi-directional Port Pin with Pull-up Function
ShiftDR
To next Cell
EXTEST
VCC
Pull-up Enable (PUE)
0
1
Output Control (OC)
FF1
Q
LD1
0
1
0
1
D
D
Q
G
Output Data (OD)
Port Pin
PXn)
0
1
FF0
Q
LD0
0
1
0
1
D
D
G
Q
Input Data (ID)
From last Cell
ClockDR
UpdateDR
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Figure 25-4. General Port Pin Schematic Diagram
See Boundary scan
Description for Details!
PUExn
PUD
Q
Q
D
DDxn
CLR
WDx
RDx
RESET
OCxn
Pxn
Q
D
ODxn
PORTxn
Q
IDxn
CLR
WRx
RRx
RESET
SLEEP
Synchronizer
RPx
D
L
Q
Q
D
Q
Q
CLR
CLKI/O
PUD:
PULL-UP DISABLE
WDX:
RDx:
WRx:
RRx:
RPx:
CLK: I/O
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
I/O CLOCK
PUExn:
OCxn:
ODxn:
IDxn:
PULL-UP ENABLE for Pin Pxn
OUTPUT CONTROL for Pin Pxn
OUTPUT DATA to Pin Pxn
INPUT DATA from Pin Pxn
SLEEP CONTROL
SLEEP:
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25.5.2 Scanning the RESET Pin
The RESET pin accepts 5V active low logic for standard reset operation, and 12V active high logic for high voltage parallel
programming. An observe-only cell as shown in Figure 25-5 is inserted for the 5V reset signal.
Figure 25-5. Observe-only Cell
ShiftDR
To next Cell
From System Pin
To System Logic
FF1
0
1
D
Q
From Previous ClockDR
Cell
25.6 ATmega164P-B/324P-B/644P-B Boundary-scan Order
Table 25-1 shows the scan order between TDI and TDO when the boundary-scan chain is selected as data path. Bit 0 is the
LSB; the first bit scanned in, and the first bit scanned out. The scan order follows the pin-out order as far as possible.
Therefore, the bits of port A and port K is scanned in the opposite bit order of the other ports. Exceptions from the rules are
the scan chains for the analog circuits, which constitute the most significant bits of the scan chain regardless of which
physical pin they are connected to. In Figure 25-3 on page 235, PXn. Data corresponds to FF0, PXn. Control corresponds to
FF1, PXn. Bit 4, 5, 6 and 7 of port F is not in the scan chain, since these pins constitute the TAP pins when the JTAG is
enabled.
Table 25-1. ATmega164P-B/324P-B/644P-B Boundary-scan Order
Bit Number
Signal Name
PB0.Data
Module
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
PB0.Control
PB1.Data
PB1.Control
PB2.Data
PB2.Control
PB3.Data
PB3.Control
PB4.Data
Port B
PB4.Control
PB5.Data
PB5.Control
PB6.Data
PB6.Control
PB7.Data
PB7.Control
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Table 25-1. ATmega164P-B/324P-B/644P-B Boundary-scan Order (Continued)
Bit Number
Signal Name
RSTT
Module
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
Reset logic (observe only)
PD0.Data
PD0.Control
PD1.Data
PD1.Control
PD2.Data
PD2.Control
PD3.Data
Port D
PD3.Control
PD4.Data
PD4.Control
PD5.Data
PD5.Control
PD6.Data
PD6.Control
PD7.Data
PD7.Control
PC0.Data
PC0.Control
PC1.Data
PC1.Control
PC6.Data
Port C
PC6.Control
PC7.Data
PC7.Control
PA7.Data
PA7.Control
PA6.Data
PA6.Control
PA5.Data
PA5.Control
PA4.Data
8
PA4.Control
PA3.Data
7
Port A
6
PA3.Control
PA2.Data
5
4
PA2.Control
PA1.Data
3
2
PA1.Control
PA0.Data
1
0
PA0.Control
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25.7 Boundary-scan Description Language Files
Boundary-scan description language (BSDL) files describe boundary-scan capable devices in a standard format used by
automated test-generation software. The order and function of bits in the boundary-scan data register are included in this
description. BSDL files are available for Atmel® ATmega164P-B/324P-B/644P-B.
25.8 Register Description
25.8.1 MCUCR – MCU Control Register
The MCU control register contains control bits for general MCU functions.
Bit
7
6
BODS
R/W
0
5
BODSE
R/W
0
4
3
–
2
–
1
IVSEL
R/W
0
0
IVCE
R/W
0
0x35 (0x55)
Read/Write
Initial Value
JTD
R/W
0
PUD
R/W
0
MCUCR
R
0
R
0
• Bits 7 – JTD: JTAG Interface Disable
When this bit is zero, the JTAG interface is enabled if the JTAGEN fuse is programmed. If this bit is one, the JTAG interface
is disabled. In order to avoid unintentional disabling or enabling of the JTAG interface, a timed sequence must be followed
when changing this bit: The application software must write this bit to the desired value twice within four cycles to change its
value. Note that this bit must not be altered when using the on-chip debug system.
25.8.2 MCUSR – MCU Status Register
The MCU status register provides information on which reset source caused an MCU reset.
Bit
7
–
6
–
5
–
4
3
2
1
0
0x34 (0x54)
Read/Write
Initial Value
JTRF
R/W
WDRF
R/W
BORF
R/W
EXTRF
R/W
PORF
R/W
MCUSR
R
0
R
0
R
0
See Bit Description
• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG reset register selected by the JTAG instruction
AVR_RESET. This bit is reset by a power-on reset, or by writing a logic zero to the flag.
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26. Boot Loader Support – Read-While-Write Self-Programming
26.1 Features
●
●
Read-while-write self-programming
Flexible boot memory size
●
High security (separate boot lock bits for a flexible protection)
Separate fuse to select reset vector
Optimized page(1) size
●
●
●
Code efficient algorithm
●
Efficient read-modify-write support
Note:
1. A page is a section in the flash consisting of several bytes (see Table 27-7 on page 258) used during
programming. The page organization does not affect normal operation.
26.2 Overview
The boot loader support provides a real read-while-write self-programming mechanism for downloading and uploading
program code by the MCU itself. This feature allows flexible application software updates controlled by the MCU using a
flash-resident boot loader program. The boot loader program can use any available data interface and associated protocol to
read code and write (program) that code into the flash memory, or read the code from the program memory. The program
code within the boot loader section has the capability to write into the entire flash, including the boot loader memory. The
boot loader can thus even modify itself, and it can also erase itself from the code if the feature is not needed anymore. The
size of the boot loader memory is configurable with fuses and the boot loader has two separate sets of boot lock bits which
can be set independently. This gives the user a unique flexibility to select different levels of protection.
26.3 Application and Boot Loader Flash Sections
The flash memory is organized in two main sections, the application section and the boot loader section (see Figure 26-2 on
page 242). The size of the different sections is configured by the BOOTSZ fuses as shown in Table 26-10 on page 251 and
Figure 26-2 on page 242. These two sections can have different level of protection since they have different sets of lock bits.
26.3.1 Application Section
The application section is the section of the flash that is used for storing the application code. The protection level for the
application section can be selected by the application boot lock bits (boot lock bits 0), see Table 26-2 on page 243. The
application section can never store any boot loader code since the SPM instruction is disabled when executed from the
application section.
26.3.2 BLS – Boot Loader Section
While the application section is used for storing the application code, the The boot loader software must be located in the
BLS since the SPM instruction can initiate a programming when executing from the BLS only. The SPM instruction can
access the entire flash, including the BLS itself. The protection level for the boot loader section can be selected by the boot
loader lock bits (boot lock bits 1), see Table 26-3 on page 243.
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26.4 Read-While-Write and No Read-While-Write Flash Sections
Whether the CPU supports read-while-write or if the CPU is halted during a boot loader software update is dependent on
which address that is being programmed. In addition to the two sections that are configurable by the BOOTSZ fuses as
described above, the flash is also divided into two fixed sections, the read-while-write (RWW) section and the no
read-while-write (NRWW) section. The limit between the RWW- and NRWW sections is given in Table 26-1 and Figure 26-1
on page 242. The main difference between the two sections is:
●
When erasing or writing a page located inside the RWW section, the NRWW section can be read during the
operation.
●
When erasing or writing a page located inside the NRWW section, the CPU is halted during the entire operation.
Note that the user software can never read any code that is located inside the RWW section during a boot loader software
operation. The syntax “read-while-write section” refers to which section that is being programmed (erased or written), not
which section that actually is being read during a boot loader software update.
26.4.1 RWW – Read-While-Write Section
If a boot loader software update is programming a page inside the RWW section, it is possible to read code from the flash,
but only code that is located in the NRWW section. During an on-going programming, the software must ensure that the
RWW section never is being read. If the user software is trying to read code that is located inside the RWW section (i.e., by
load program memory, call, or jump instructions or an interrupt) during programming, the software might end up in an
unknown state. To avoid this, the interrupts should either be disabled or moved to the boot loader section. The boot loader
section is always located in the NRWW section. The RWW section busy bit (RWWSB) in the store program memory control
and status register (SPMCSR) will be read as logical one as long as the RWW section is blocked for reading. After a
programming is completed, the RWWSB must be cleared by software before reading code located in the RWW section. See
Section 26.9.1 “SPMCSR – Store Program Memory Control and Status Register” on page 253 for details on how to clear
RWWSB.
26.4.2 NRWW – No Read-While-Write Section
The code located in the NRWW section can be read when the boot loader software is updating a page in the RWW section.
When the boot loader code updates the NRWW section, the CPU is halted during the entire page erase or page write
operation.
Table 26-1. Read-While-Write Features
Which Section Can be
Which Section does the Z-pointer Address
During the Programming?
Read During
Programming?
Is the CPU
Halted?
Read-While-Write
Supported?
RWW section
NRWW section
None
No
Yes
No
NRWW section
Yes
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Figure 26-1. Read-while-write versus No Read-while-write
Read While Write
(RWW) Section
Z-pointer
Addresses NRWW
Section
Z-pointer
Addresses RWW
Section
No Read While Write
(RWW) Section
CPU is Halted During
the Operation
Code located in
NRWW Section
can be Read During
the Operation
Figure 26-2. Memory Sections
Program Memory
BOOTSZ = ’11’
Program Memory
BOOTSZ = ’10’
0x0000
0x0000
Application Flash Section
Application Flash Section
End RWW
End RWW
Start NRWW
Start NRWW
Application Flash Section
Boot Loader Flash Section
Application Flash Section
Boot Loader Flash Section
End Application
Start Boot Loader
End Application
Start Boot Loader
Flashend
Flashend
Program Memory
BOOTSZ = ’01’
Program Memory
BOOTSZ = ’00’
0x0000
0x0000
Application Flash Section
Application Flash Section
End RWW
End RWW, End Application
Start NRWW
Start NRWW, Start Boot Loader
Application Flash Section
Boot Loader Flash Section
End Application
Start Boot Loader
Boot Loader Flash Section
Flashend
Flashend
Note:
The parameters in the figure above are given in Table 26-10 on page 251.
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26.5 Boot Loader Lock Bits
If no boot loader capability is needed, the entire flash is available for application code. The boot loader has two separate sets
of boot lock bits which can be set independently. This gives the user a unique flexibility to select different levels of protection.
The user can select:
●
●
●
●
To protect the entire flash from a software update by the MCU.
To protect only the boot loader flash section from a software update by the MCU.
To protect only the application flash section from a software update by the MCU.
Allow software update in the entire flash.
See Table 26-2 and Table 26-3 for further details. The boot lock bits can be set in software and in serial or parallel
programming mode, but they can be cleared by a chip erase command only. The general write lock (Lock bit mode 2) does
not allow the programming of the flash memory by SPM instruction. Similarly, the general read/write lock (Lock bit mode 3)
does not allow reading nor writing by (E)LPM/SPM, if it is attempted.
Table 26-2. Boot Lock Bit0 Protection Modes (Application Section)(1)
BLB0 Mode
BLB02
BLB01
Protection
1
2
1
1
1
0
No restrictions for SPM or (E)LPM accessing the application section.
SPM is not allowed to write to the application section.
SPM is not allowed to write to the application section, and (E)LPM executing
from the boot loader section is not allowed to read from the application
section. If interrupt vectors are placed in the boot loader section, interrupts
are disabled while executing from the application section.
3
0
0
(E)LPM executing from the boot loader section is not allowed to read from
the application section. If interrupt vectors are placed in the boot loader
section, interrupts are disabled while executing from the application section.
4
0
1
Note:
1. “1” means unprogrammed, “0” means programmed
Table 26-3. Boot Lock Bit1 Protection Modes (Boot Loader Section)(1)
BLB1 Mode
BLB12
BLB11
Protection
1
2
1
1
1
0
No restrictions for SPM or (E)LPM accessing the boot loader section.
SPM is not allowed to write to the boot loader section.
SPM is not allowed to write to the boot loader section, and (E)LPM executing
from the application section is not allowed to read from the boot loader
section. If interrupt vectors are placed in the application section, interrupts
are disabled while executing from the boot loader section.
3
0
0
(E)LPM executing from the application section is not allowed to read from the
boot loader section. If interrupt vectors are placed in the application section,
interrupts are disabled while executing from the boot loader section.
4
0
1
Note:
1. “1” means unprogrammed, “0” means programmed
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26.6 Entering the Boot Loader Program
Entering the boot loader takes place by a jump or call from the application program. This may be initiated by a trigger such
as a command received via USART, or SPI interface. Alternatively, the boot reset fuse can be programmed so that the reset
vector is pointing to the boot flash start address after a reset. In this case, the boot loader is started after a reset. After the
application code is loaded, the program can start executing the application code. Note that the fuses cannot be changed by
the MCU itself. This means that once the boot reset fuse is programmed, the reset vector will always point to the boot loader
reset and the fuse can only be changed through the serial or parallel programming interface.
Table 26-4. Boot Reset Fuse(1)
BOOTRST
Reset Address
1
0
Reset vector = application reset (address 0x0000)
Reset vector = boot loader reset (see Table 26-10 on page 251)
Note:
1. “1” means unprogrammed, “0” means programmed
26.7 Addressing the Flash During Self-programming
The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers ZL and ZH in the register file,
and RAMPZ in the I/O space. The number of bits actually used is implementation dependent. Note that the RAMPZ register
is only implemented when the program space is larger than 64Kbytes.
Bit
23
15
22
14
21
13
20
12
19
11
18
10
17
16
9
8
RAMPZ
ZH (R31)
ZL (R30)
RAMPZ7
Z15
Z7
RAMPZ6
Z14
Z6
RAMPZ5
Z13
Z5
RAMPZ4
Z12
Z4
RAMPZ3
Z11
RAMPZ2
Z10
Z2
RAMPZ1
RAMPZ0
Z9
Z1
1
Z8
Z0
0
Z3
7
6
5
4
3
2
Since the flash is organized in pages (see Table 27-7 on page 258), the program counter can be treated as having two
different sections. One section, consisting of the least significant bits, is addressing the words within a page, while the most
significant bits are addressing the pages. This is shown in Figure 26-3 on page 245. Note that the page erase and page write
operations are addressed independently. Therefore it is of major importance that the boot loader software addresses the
same page in both the page erase and page write operation. Once a programming operation is initiated, the address is
latched and the Z-pointer can be used for other operations.
The LPM instruction use the Z-pointer to store the address. Since this instruction addresses the flash byte-by-byte, also bit
Z0 of the Z-pointer is used.
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Figure 26-3. Addressing the Flash During SPM(1)
BIT
15
ZPCMSB
ZPAGEMSB 1 0
0
Z-REGISTER
PCMSB
PAGEMSB
PCWORD
PROGRAM
COUNTER
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN PAGE
Program Memory
Page
Page
Instructions Word
PCWORD [PAGEMSB : 0]
00
01
02
PAGEEND
Note:
1. The different variables used in Figure 26-3 are listed in Table 26-12 on page 252.
26.8 Self-Programming the Flash
The program memory is updated in a page by page fashion. Before programming a page with the data stored in the
temporary page buffer, the page must be erased. The temporary page buffer is filled one word at a time using SPM and the
buffer can be filled either before the page erase command or between a page erase and a page write operation:
Alternative 1, fill the buffer before a page erase
●
●
●
Fill temporary page buffer
Perform a page erase
Perform a page write
Alternative 2, fill the buffer after page erase
●
●
●
Perform a page erase
Fill temporary page buffer
Perform a page write
If only a part of the page needs to be changed, the rest of the page must be stored (for example in the temporary page
buffer) before the erase, and then be rewritten. When using alternative 1, the boot loader provides an effective
read-modify-write feature which allows the user software to first read the page, do the necessary changes, and then write
back the modified data. If alternative 2 is used, it is not possible to read the old data while loading since the page is already
erased. The temporary page buffer can be accessed in a random sequence. It is essential that the page address used in
both the page erase and page write operation is addressing the same page. See Section 26.8.13 “Simple Assembly Code
Example for a Boot Loader” on page 249 for an assembly code example.
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26.8.1 Performing Page Erase by SPM
To execute page erase, set up the address in the Z-pointer, write “X0000011” to SPMCSR and execute SPM within four
clock cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE in the
Z-register. Other bits in the Z-pointer will be ignored during this operation.
●
●
Page erase to the RWW section: The NRWW section can be read during the page erase.
Page erase to the NRWW section: The CPU is halted during the operation.
Note:
If an interrupt occurs in the time sequence, the four cycle access cannot be guaranteed. In order to ensure
atomic operation, you should disable interrupts before writing to SPMCSR.
26.8.2 Filling the Temporary Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write “00000001” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The content of PCWORD in the Z-register is used to address
the data in the temporary buffer. The temporary buffer will auto-erase after a page write operation or by writing the
RWWSRE bit in SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than one time to
each address without erasing the temporary buffer.
If the EEPROM is written in the middle of an SPM page load operation, all data loaded will be lost.
26.8.3 Performing a Page Write
To execute page write, set up the address in the Z-pointer, write “X0000101” to SPMCSR and execute SPM within four clock
cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE. Other bits
in the Z-pointer must be written to zero during this operation.
●
●
Page write to the RWW section: The NRWW section can be read during the page write.
Page write to the NRWW section: The CPU is halted during the operation.
26.8.4 Using the SPM Interrupt
If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt when the SPMEN bit in SPMCSR is
cleared. This means that the interrupt can be used instead of polling the SPMCSR register in software. When using the SPM
interrupt, the interrupt vectors should be moved to the BLS section to avoid that an interrupt is accessing the RWW section
when it is blocked for reading. How to move the interrupts is described in Section 12. “Interrupts” on page 49.
26.8.5 Consideration While Updating BLS
Special care must be taken if the user allows the boot loader section to be updated by leaving boot lock bit11
unprogrammed. An accidental write to the boot loader itself can corrupt the entire boot loader, and further software updates
might be impossible. If it is not necessary to change the boot loader software itself, it is recommended to program the boot
lock bit11 to protect the boot loader software from any internal software changes.
26.8.6 Prevent Reading the RWW Section During Self-Programming
During self-programming (either page erase or page write), the RWW section is always blocked for reading. The user
software itself must prevent that this section is addressed during the self programming operation. The RWWSB in the
SPMCSR will be set as long as the RWW section is busy. During self-programming the interrupt vector table should be
moved to the BLS as described in Section 12. “Interrupts” on page 49, or the interrupts must be disabled. Before addressing
the RWW section after the programming is completed, the user software must clear the RWWSB by writing the RWWSRE.
See Section 26.8.13 “Simple Assembly Code Example for a Boot Loader” on page 249 for an example.
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26.8.7 Setting the Boot Loader Lock Bits by SPM
To set the boot loader lock bits and general lock bits, write the desired data to R0, write “X0001001” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR.
Bit
R0
7
6
5
4
3
2
1
0
1
1
BLB12
BLB11
BLB02
BLB01
LB2
LB1
See Table 26-2 on page 243 and Table 26-3 on page 243 for how the different settings of the boot loader bits affect the flash
access.
If bits 5..0 in R0 are cleared (zero), the corresponding boot lock bit will be programmed if an SPM instruction is executed
within four cycles after BLBSET and SPMEN are set in SPMCSR. The Z-pointer is don’t care during this operation, but for
future compatibility it is recommended to load the Z-pointer with 0x0001 (same as used for reading the lOck bits). For future
compatibility it is also recommended to set bits 7 and 6 in R0 to “1” when writing the lock bits. When programming the lock
bits the entire flash can be read during the operation.
26.8.8 EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to flash. Reading the fuses and lock bits from
software will also be prevented during the EEPROM write operation. It is recommended that the user checks the status bit
(EEPE) in the EECR register and verifies that the bit is cleared before writing to the SPMCSR register.
26.8.9 Reading the Fuse and Lock Bits from Software
It is possible to read both the fuse and lock bits from software. To read the lock bits, load the Z-pointer with 0x0001 and set
the BLBSET and SPMEN bits in SPMCSR. When an (E)LPM instruction is executed within three CPU cycles after the
BLBSET and SPMEN bits are set in SPMCSR, the value of the lock bits will be loaded in the destination register. The
BLBSET and SPMEN bits will auto-clear upon completion of reading the lock bits or if no (E)LPM instruction is executed
within three CPU cycles or no SPM instruction is executed within four CPU cycles. When BLBSET and SPMEN are cleared,
(E)LPM will work as described in the instruction set manual.
Bit
Rd
7
–
6
–
5
4
3
2
1
0
BLB12
BLB11
BLB02
BLB01
LB2
LB1
The algorithm for reading the fuse low byte is similar to the one described above for reading the lock bits. To read the fuse
low byte, load the Z-pointer with 0x0000 and set the BLBSET and SPMEN bits in SPMCSR. When an (E)LPM instruction is
executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR, the value of the fuse low byte (FLB)
will be loaded in the destination register as shown below. Refer to Table 27-5 on page 257 for a detailed description and
mapping of the fuse low byte.
Bit
Rd
7
6
5
4
3
2
1
0
FLB7
FLB6
FLB5
FLB4
FLB3
FLB2
FLB1
FLB0
Similarly, when reading the fuse high byte, load 0x0003 in the Z-pointer. When an (E)LPM instruction is executed within
three cycles after the BLBSET and SPMEN bits are set in the SPMCSR, the value of the fuse high byte (FHB) will be loaded
in the destination register as shown below. Refer to Table 27-4 on page 257 for detailed description and mapping of the fuse
high byte.
Bit
Rd
7
6
5
4
3
2
1
0
FHB7
FHB6
FHB5
FHB4
FHB3
FHB2
FHB1
FHB0
When reading the extended fuse byte, load 0x0002 in the Z-pointer. When an (E)LPM instruction is executed within three
cycles after the BLBSET and SPMEN bits are set in the SPMCSR, the value of the extended fuse byte (EFB) will be loaded
in the destination register as shown below. Refer to Table 27-3 on page 256 for detailed description and mapping of the
extended fuse byte.
Bit
Rd
7
–
6
–
5
–
4
–
3
–
2
1
0
EFB2
EFB1
EFB0
Fuse and lock bits that are programmed, will be read as zero. Fuse and lock bits that are unprogrammed, will be read as
one.
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26.8.10 Reading the Signature Row from Software
To read the signature row from software, load the Z-pointer with the signature byte address given in Table 26-5 and set the
SIGRD and SPMEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the SIGRD and
SPMEN bits are set in SPMCSR, the signature byte value will be loaded in the destination register. The SIGRD and SPMEN
bits will auto-clear upon completion of reading the signature row lock bits or if no LPM instruction is executed within three
CPU cycles. When SIGRD and SPMEN are cleared, LPM will work as described in the instruction set manual.
Table 26-5. Signature Row Addressing
Signature Byte
Device signature byte 1
Device signature byte 2
Device signature byte 3
RC oscillator calibration byte 3V
Z-Pointer Address
0x0000
0x0002
0x0004
0x0001
RC oscillator calibration byte 5V
0x0003
Note:
All other addresses are reserved for future use.
26.8.11 Preventing Flash Corruption
During periods of low VCC, the flash program can be corrupted because the supply voltage is too low for the CPU and the
flash to operate properly. These issues are the same as for board level systems using the flash, and the same design
solutions should be applied.
A flash program corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to
the flash requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the
supply voltage for executing instructions is too low.
Flash corruption can easily be avoided by following these design recommendations (one is sufficient):
1. If there is no need for a boot loader update in the system, program the boot loader lock bits to prevent any boot
loader software updates.
2. Keep the AVR® RESET active (low) during periods of insufficient power supply voltage. This can be done by
enabling the internal brown-out detector (BOD) if the operating voltage matches the detection level. If not, an
external low VCC reset protection circuit can be used. If a reset occurs while a write operation is in progress, the
write operation will be completed provided that the power supply voltage is sufficient.
3. Keep the AVR core in power-down sleep mode during periods of low VCC. This will prevent the CPU from
attempting to decode and execute instructions, effectively protecting the SPMCSR register and thus the flash from
unintentional writes.
26.8.12 Programming Time for Flash when Using SPM
The calibrated RC oscillator is used to time flash accesses. Table 26-6 shows the typical programming time for flash
accesses from the CPU.
Table 26-6. SPM Programming Time(1)
Symbol
Min Programming Time
Max Programming Time
Flash write (page erase, page write, and write lock
bits by SPM)
3.7ms
4.5ms
Note:
1. Minimum and maximum programming times is per individual operation.
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26.8.13 Simple Assembly Code Example for a Boot Loader
;-the routine writes one page of data from RAM to Flash
; the first data location in RAM is pointed to by the Y pointer
; the first data location in Flash is pointed to by the Z-pointer
;-error handling is not included
;-the routine must be placed inside the Boot space
; (at least the Do_spm sub routine). Only code inside NRWW section can
; be read during Self-Programming (Page Erase and Page Write).
;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),
; loophi (r25), spmcrval (r20)
; storing and restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
;-It is assumed that either the interrupt table is moved to the Boot
; loader section or that the interrupts are disabled.
PAGESIZEB = PAGESIZE*2;PAGESIZEB is page size in BYTES, not words
.equ
.org SMALLBOOTSTART
Write_page:
;Page Erase
ldi
call
spmcrval, (1<<PGERS) | (1<<SPMEN)
Do_spm
;re-enable the RWW section
ldi
call
spmcrval, (1<<RWWSRE) | (1<<SPMEN)
Do_spm
;transfer data from RAM to Flash page buffer
ldi
ldi
looplo, low(PAGESIZEB)
loophi, high(PAGESIZEB)
;init loop variable
;not required for PAGESIZEB<=256
Wrloop:
ld
ld
r0, Y+
r1, Y+
ldi
call
adiw
sbiw
brne
spmcrval, (1<<SPMEN)
Do_spm
ZH:ZL, 2
loophi:looplo, 2
Wrloop
;use subi for PAGESIZEB<=256
;execute Page Write
subi
sbci
ldi
ZL, low(PAGESIZEB)
ZH, high(PAGESIZEB)
;restore pointer
;not required for PAGESIZEB<=256
spmcrval, (1<<PGWRT) | (1<<SPMEN)
Do_spm
call
;re-enable the RWW section
ldi
call
spmcrval, (1<<RWWSRE) | (1<<SPMEN)
Do_spm
;read back and check, optional
ldi
ldi
looplo, low(PAGESIZEB)
loophi, high(PAGESIZEB)
YL, low(PAGESIZEB)
;init loop variable
;not required for PAGESIZEB<=256
;restore pointer
subi
sbci
YH, high(PAGESIZEB)
Rdloop:
lpm
ld
r0, Z+
r1, Y+
cpse
jmp
r0, r1
Error
sbiw
brne
loophi:looplo, 1
Rdloop
;use subi for PAGESIZEB<=256
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;return to RWW section
;verify that RWW section is safe to read
Return:
in
sbrs
ready yet
ret
;re-enable the RWW section
temp1, SPMCSR
temp1, RWWSB
; If RWWSB is set, the RWW section is not
ldi
call
rjmp
spmcrval, (1<<RWWSRE) | (1<<SPMEN)
Do_spm
Return
Do_spm:
;check for previous SPM complete
Wait_spm:
in
temp1, SPMCSR
temp1, SPMEN
Wait_spm
sbrc
rjmp
;
input: spmcrval determines SPM action
disable interrupts if enabled, store status
temp2, SREG
;
in
cli
;check that no EEPROM write access is present
Wait_ee:
sbic
EECR, EEPE
rjmp
;
Wait_ee
SPM timed sequence
SPMCSR, spmcrval
out
spm
;restore SREG (to enable interrupts if originally enabled)
out
ret
SREG, temp2
26.8.14 ATmega164P-B Boot Loader Parameters
In Table 26-7 through Table 26-9 on page 251, the parameters used in the description of the self-programming are given.
Table 26-7. Boot Size Configuration(1)
Boot Reset
End
Application
Section
Address
(Start Boot
Loader Section)
Application
Boot Loader
BOOTSZ1 BOOTSZ0 Boot Size Pages
Flash Section
Flash Section
1
1
0
0
1
0
1
0
128 words
256 words
512 words
1024 words
2
4
0x0000 - 0x1F7F 0x1F80 - 0x1FFF
0x0000 - 0x1EFF 0x1F00 - 0x1FFF
0x0000 - 0x1DFF 0x1E00 - 0x1FFF
0x0000 - 0x1BFF 0x1C00 - 0x1FFF
0x1F7F
0x1EFF
0x1DFF
0x1BFF
0x1F80
0x1F00
0x1E00
0x1C00
8
16
Note:
1. The different BOOTSZ fuse configurations are shown in Figure 26-2 on page 242.
Table 26-8. Read-While-Write Limit(1)
Section
Pages
112
Address
Read-while-write section (RWW)
No read-while-write section (NRWW)
0x0000 - 0x1BFF
0x1C00 - 0x1FFF
16
Note:
1. For details about these two sections, see Section 26.4.2 “NRWW – No Read-While-Write Section” on page
241 and Section 26.4.1 “RWW – Read-While-Write Section” on page 241.
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Table 26-9. Explanation of Different Variables used in Figure 26-3 on page 245 and the Mapping to the Z-pointer
Corresponding
Variable
Z-value
Description(1)
Most significant bit in the program counter. (The program counter is 13
bits PC[12:0])
PCMSB
12
5
Most significant bit which is used to address the words within one page
(128 words in a page requires seven bits PC [5:0]).
PAGEMSB
ZPCMSB
Bit in Z-pointer that is mapped to PCMSB. Because Z0 is not used, the
ZPCMSB equals PCMSB + 1.
Z13
Z6
Bit in Z-pointer that is mapped to PCMSB. Because Z0 is not used, the
ZPAGEMSB equals PAGEMSB + 1.
ZPAGEMSB
PCPAGE
Program counter page address: Page select, for page erase and page
write
PC[12:6]
PC[5:0]
Z14:Z7
Z6:Z1
Program counter word address: Word select, for filling temporary buffer
(must be zero during page write operation)
PCWORD
Note:
1. Z0: should be zero for all SPM commands, byte select for the (E)LPM instruction.
See Section 26.7 “Addressing the Flash During Self-programming” on page 244 for details about the use of Z-pointer
during self-programming.
26.8.15 ATmega324P-B Boot Loader Parameters
In Table 26-10 through Table 26-12 on page 252, the parameters used in the description of the self-programming are given.
Table 26-10. Boot Size Configuration(1)
Boot Reset
End
Application
Section
Address
(Start Boot
Loader Section)
Application
Boot Loader
BOOTSZ1 BOOTSZ0 Boot Size Pages
Flash Section
Flash Section
1
1
0
0
1
0
1
0
256 words
512 words
1024 words
2048 words
4
8
0x0000 - 0x3EFF 0x3F00 - 0x3FFF
0x0000 - 0x1DFF 0x3E00 - 0x3FFF
0x0000 - 0x1BFF 0x3C00 - 0x3FFF
0x0000 - 0x37FF 0x3800 - 0x3FFF
0x3EFF
0x3DFF
0x3BFF
0x37FF
0x3F00
0x3E00
0x3C00
0x3800
16
32
Note:
1. The different BOOTSZ fuse configurations are shown in Figure 26-2 on page 242.
Table 26-11. Read-While-Write Limit(1)
Section
Pages
224
Address
Read-while-write section (RWW)
No read-while-write section (NRWW)
0x0000 - 0x37FF
0x3800 - 0x3FFF
32
Note:
1. For details about these two sections, see Section 26.4.2 “NRWW – No Read-While-Write Section” on page
241 and Section 26.4.1 “RWW – Read-While-Write Section” on page 241.
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Table 26-12. Explanation of Different Variables used in Figure 26-3 on page 245 and the Mapping to the Z-pointer
Corresponding
Variable
Z-value
Description(1)
Most significant bit in the program counter. (The program counter is 14 bits
PC[13:0])
PCMSB
13
6
Most significant bit which is used to address the words within one page
(128 words in a page requires seven bits PC [5:0]).
PAGEMSB
ZPCMSB
Bit in Z-pointer that is mapped to PCMSB. Because Z0 is not used, the
ZPCMSB equals PCMSB + 1.
Z14
Z7
Bit in Z-pointer that is mapped to PCMSB. Because Z0 is not used, the
ZPAGEMSB equals PAGEMSB + 1.
ZPAGEMSB
PCPAGE
Program counter page address: page select, for page erase and page
write
PC[13:6]
PC[5:0]
Z14:Z7
Z6:Z1
Program counter word address: Word select, for filling temporary buffer
(must be zero during page write operation)
PCWORD
Note:
1. 0: should be zero for all SPM commands, byte select for the (E)LPM instruction.
See Section 26.7 “Addressing the Flash During Self-programming” on page 244 for details about the use of Z-pointer
during self-programming.
26.8.16 ZATmega644P-B Boot Loader Parameters
In Table 26-13 through Table 26-15 on page 253, the parameters used in the description of the self-programming are given.
Table 26-13. Boot Size Configuration(1)
Boot Reset
End
Application
Section
Address
(Start Boot
Loader Section)
Application
Boot Loader
BOOTSZ1 BOOTSZ0 Boot Size Pages
Flash Section
Flash Section
1
1
0
0
1
0
1
0
512 words
1024 words
2048 words
4096 words
4
8
0x0000 - 0x7DFF 0x7E00 - 0x7FFF
0x0000 - 0x7BFF 0x7C00 - 0x7FFF
0x0000 - 0x77FF 0x7800 - 0x7FFF
0x0000 - 0x6FFF 0x7000 - 0x7FFF
0x7DFF
0x7BFF
0x77FF
0x6FFF
0x7E00
0x7C00
0x7800
0x7000
16
32
Note:
1. The different BOOTSZ fuse configurations are shown in Figure 26-2 on page 242.
Table 26-14. Read-while-write Limit(1)
Section
Pages
224
Address
Read-while-write section (RWW)
No read-while-write section (NRWW)
0x0000 - 0x6FFF
0x7000 - 0x7FFF
32
Note:
1. For details about these two sections, see Section 26.4.2 “NRWW – No Read-While-Write Section” on page
241 and Section 26.4.1 “RWW – Read-While-Write Section” on page 241.
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Table 26-15. Explanation of Different Variables used in Figure 26-3 on page 245 and the Mapping to the Z-pointer
Corresponding
Variable
Z-value
Description(1)
Most significant bit in the program counter. (The program counter is 14 bits
PC[14:0])
PCMSB
14
7
Most significant bit which is used to address the words within one page
(128 words in a page requires seven bits PC [6:0]).
PAGEMSB
ZPCMSB
Bit in Z-pointer that is mapped to PCMSB. Because Z0 is not used, the
ZPCMSB equals PCMSB + 1.
Z15
Z8
Bit in Z-pointer that is mapped to PCMSB. Because Z0 is not used, the
ZPAGEMSB equals PAGEMSB + 1.
ZPAGEMSB
PCPAGE
Program counter page address: page select, for page erase and page
write
PC[14:7]
PC[6:0]
Z15:Z7
Z7:Z1
Program counter word address: word select, for filling temporary buffer
(must be zero during page write operation)
PCWORD
Note:
1. Z0: should be zero for all SPM commands, byte select for the (E)LPM instruction.
See Section 26.7 “Addressing the Flash During Self-programming” on page 244 for details about the use of Z-pointer during
self-programming.
26.9 Register Description
26.9.1 SPMCSR – Store Program Memory Control and Status Register
The store program memory control and status register contains the control bits needed to control the boot loader operations.
Bit
7
6
5
4
3
2
1
0
0x37 (0x57) SPMIE RWWSB SIGRD RWWSRE BLBSET PGWRT PGERS SPMEN SPMCSR
Read/Write
Initial Value
R/W
0
R
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the status register is set (one), the SPM ready interrupt will be enabled.
The SPM ready interrupt will be executed as long as the SPMEN bit in the SPMCSR register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a self-programming (page erase or page write) operation to the RWW section is initiated, the RWWSB will be set
(one) by hardware. When the RWWSB bit is set, the RWW section cannot be accessed. The RWWSB bit will be cleared if
the RWWSRE bit is written to one after a self-programming operation is completed. Alternatively the RWWSB bit will
automatically be cleared if a page load operation is initiated.
• Bit 5 – SIGRD: Signature Row Read
If this bit is written to one at the same time as SPMEN, the next LPM instruction within three clock cycles will read a byte from
the signature row into the destination register. see Section 26.8.10 “Reading the Signature Row from Software” on page 248
for details. An SPM instruction within four cycles after SIGRD and SPMEN are set will have no effect. This operation is
reserved for future use and should not be used.
• Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (page erase or page write) to the RWW section, the RWW section is blocked for reading (the RWWSB
will be set by hardware). To re-enable the RWW section, the user software must wait until the programming is completed
(SPMEN will be cleared). Then, if the RWWSRE bit is written to one at the same time as SPMEN, the next SPM instruction
within four clock cycles re-enables the RWW section. The RWW section cannot be re-enabled while the flash is busy with a
page erase or a page write (SPMEN is set). If the RWWSRE bit is written while the flash is being loaded, the flash load
operation will abort and the data loaded will be lost.
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• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock cycles sets boot lock bits,
according to the data in R0. The data in R1 and the address in the Z-pointer are ignored. The BLBSET bit will automatically
be cleared upon completion of the lock bit set, or if no SPM instruction is executed within four clock cycles.
An (E)LPM instruction within three cycles after BLBSET and SPMEN are set in the SPMCSR register, will read either the
lock bits or the fuse bits (depending on Z0 in the Z-pointer) into the destination register. See Section 26.8.9 “Reading the
Fuse and Lock Bits from Software” on page 247 for details.
• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock cycles executes page write,
with the data stored in the temporary buffer. The page address is taken from the high part of the Z-pointer. The data in R1
and R0 are ignored. The PGWRT bit will auto-clear upon completion of a page write, or if no SPM instruction is executed
within four clock cycles. The CPU is halted during the entire page write operation if the NRWW section is addressed.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock cycles executes page
erase. The page address is taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGERS bit will
auto-clear upon completion of a page erase, or if no SPM instruction is executed within four clock cycles. The CPU is halted
during the entire page write operation if the NRWW section is addressed.
• Bit 0 – SPMEN: Store Program Memory Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one together with either RWWSRE, BLBSET,
PGWRT’ or PGERS, the following SPM instruction will have a special meaning, see description above. If only SPMEN is
written, the following SPM instruction will store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer.
The LSB of the Z-pointer is ignored. The SPMEN bit will auto-clear upon completion of an SPM instruction, or if no SPM
instruction is executed within four clock cycles. During page erase and page write, the SPMEN bit remains high until the
operation is completed.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the lower five bits will have no effect.
Note:
Only one SPM instruction should be active at any time.
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27. Memory Programming
27.1 Program And Data Memory Lock Bits
The Atmel® ATmega164P-B/324P-B/644P-B provides six lock bits which can be left unprogrammed (“1”) or can be
programmed (“0”) to obtain the additional features listed in Table 27-2. The lock bits can only be erased to “1” with the chip
erase command.
Table 27-1. Lock Bit Byte(1)
Lock Bit Byte
Bit No
Description
–
Default Value
7
6
5
4
3
2
1
0
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
–
BLB12
BLB11
BLB02
BLB01
LB2
Boot lock bit
Boot lock bit
Boot lock bit
Boot lock bit
Lock bit
LB1
Lock bit
Note:
1. “1” means unprogrammed, “0” means programmed.
Table 27-2. Lock Bit Protection Modes(1)(2)
Memory Lock Bits
Protection Type
LB Mode
1
LB2
1
LB1
1
No memory lock features enabled.
Further programming of the flash and EEPROM is disabled in parallel and
serial programming mode. The fuse bits are locked in both serial and parallel
programming mode.(1)
2
3
1
0
0
0
Further programming and verification of the flash and EEPROM is disabled in
parallel, JTAG and serial programming mode. The boot lock bits and fuse bits
are locked in both serial and parallel programming mode.(1)
BLB0 Mode
BLB02
BLB01
1
2
1
1
1
0
No restrictions for SPM or (E)LPM accessing the application section.
SPM is not allowed to write to the application section.
SPM is not allowed to write to the application section, and (E)LPM executing
from the boot loader section is not allowed to read from the application
section. If interrupt vectors are placed in the boot loader section, interrupts
are disabled while executing from the application section.
3
0
0
(E)LPM executing from the boot loader section is not allowed to read from
the application section. If interrupt vectors are placed in the boot loader
section, interrupts are disabled while executing from the application section.
4
0
1
Notes: 1. Program the fuse bits and boot lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
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Table 27-2. Lock Bit Protection Modes(1)(2) (Continued)
Memory Lock Bits
Protection Type
BLB1 Mode
BLB12
BLB11
1
2
1
1
1
0
No restrictions for SPM or (E)LPM accessing the boot loader section.
SPM is not allowed to write to the boot loader section.
SPM is not allowed to write to the boot loader section, and (E)LPM executing
from the application section is not allowed to read from the boot loader
section. If interrupt vectors are placed in the application section, interrupts
are disabled while executing from the boot loader section.
3
0
0
(E)LPM executing from the application section is not allowed to read from the
boot loader section. If interrupt vectors are placed in the application section,
interrupts are disabled while executing from the boot loader section.
4
0
1
Notes: 1. Program the fuse bits and boot lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
27.2 Fuse Bits
The Atmel® ATmega164P-B/324P-B/644P-B has four fuse bytes. Table 27-3 - Table 27-5 on page 257 describe briefly the
functionality of all the fuses and how they are mapped into the fuse bytes. Note that the fuses are read as logical zero, “0”, if
they are programmed.
Table 27-3. Extended Fuse Byte
Fuse Low Byte
Bit No
Description
Default Value
–
7
6
5
4
3
2
1
0
–
1
–
–
1
–
–
1
–
–
1
–
–
1
BODLEVEL2(1)
BODLEVEL1(1)
BODLEVEL0(1)
Brown-out detector trigger level
Brown-out detector trigger level
Brown-out detector trigger level
1 (unprogrammed)
0 (programmed)
1 (unprogrammed)
Note:
1. See Section 28.5 “System and Reset Characteristics” on page 291 for BODLEVEL fuse decoding
(default = 2.7V).
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Table 27-4. Fuse High Byte
Fuse High Byte
OCDEN(4)
JTAGEN
Bit No
Description
Enable OCD
Enable JTAG
Default Value
7
6
5
4
1 (unprogrammed, OCD disabled)
0 (programmed, JTAG enabled)
SPIEN(1)
WDTON(3)
Enable serial program and data downloading 0 (programmed, SPI prog. enabled)
Watchdog timer always on 1 (unprogrammed)
EEPROM memory is preserved through the 1 (unprogrammed, EEPROM not
EESAVE
3
2
chip erase
preserved)
Select boot size (see Table 27-9 on page 259
for details)
BOOTSZ1
0 (programmed)(2)
Select boot size (see Table 27-9 on page 259
for details)
BOOTSZ0
BOOTRST
1
0
0 (programmed)(2)
1 (unprogrammed)
Select reset vector
Notes: 1. The SPIEN fuse is not accessible in serial programming mode.
2. The default value of BOOTSZ1..0 results in maximum boot size. See Table 26-10 on page 251 for details.
3. See Section 11.4.2 “WDTCSR – Watchdog Timer Control Register” on page 47 for details.
4. Never ship a product with the OCDEN fuse programmed regardless of the setting of lock bits and JTAGEN
fuse. A programmed OCDEN fuse enables some parts of the clock system to be running in all sleep modes.
This may increase the power consumption.
Table 27-5. Fuse Low Byte
Fuse Low Byte
CKDIV8(4)
CKOUT(3)
SUT1
Bit No
Description
Default Value
0 (programmed)
7
6
5
4
3
2
1
0
Divide clock by 8
Clock output
1 (unprogrammed)
1 (unprogrammed)(1)
0 (programmed)(1)
0 (programmed)(2)
0 (programmed)(2)
1 (unprogrammed)(2)
0 (programmed)(2)
Select start-up time
Select start-up time
Select clock source
Select clock source
Select clock source
Select clock source
SUT0
CKSEL3
CKSEL2
CKSEL1
CKSEL0
Notes: 1. The default value of SUT1..0 results in maximum start-up time for the default clock source. See Section 28.5
“System and Reset Characteristics” on page 291 for details.
2. The default setting of CKSEL3..0 results in internal RC oscillator at 8MHz. See Table 9-1 on page 24 for
details.
3. The CKOUT fuse allow the system clock to be output on PORTB1. See Section 9.10 “Clock Output Buffer” on
page 31 for details.
4. See Section 9.11 “System Clock Prescaler” on page 31 for details.
The status of the fuse bits is not affected by chip erase. Note that the fuse bits are locked if lock bit1 (LB1) is programmed.
Program the fuse bits before programming the lock bits.
27.2.1 Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of the fuse values will have no effect
until the part leaves programming mode. This does not apply to the EESAVE fuse which will take effect once it is
programmed. The fuses are also latched on power-up in normal mode.
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27.3 Signature Bytes
All Atmel® microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial
and parallel mode, also when the device is locked. The three bytes reside in a separate address space.
For the Atmel ATmega164P-B/324P-B/644P-B the signature bytes are given in Table 27-6.
Table 27-6. Device and JTAG ID
Signature Bytes Address
JTAG
Part
0x000
0x001
0x94
0x95
0x96
0x002
Part Number
940A
Manufacture ID
0x1F
ATmega164P-B
ATmega324P-B
ATmega644P-B
0x1E
0x1E
0x1E
0x0A
0x11
0x0A
9511
0x1F
960A
0x1F
27.4 Calibration Byte
The Atmel ATmega164P-B/324P-B/644P-B has a byte 2 calibration values for the internal RC oscillator. The 3V calibration
byte resides in the address 0x0001 in the signature address space and the 5V calibration byte resides in the address
0x0003. During reset, the 3V calibration byte is automatically written into the OSCCAL register to ensure correct frequency
of the calibrated RC oscillator.
27.5 Page Size
Table 27-7. No. of Words in a Page and No. of Pages in the Flash
Device
Flash Size
Page Size
64 words
64 words
PCWORD No. of Pages PCPAGE
PCMSB
12
ATmega164P-B
ATmega324P-B
ATmega644P-B
8K words (16Kbytes)
16K words (32Kbytes)
PC[5:0]
PC[5:0]
PC[6:0]
128
256
256
PC[12:6]
PC[13:6]
PC[14:6]
13
32K words (64Kbytes) 128 words
14
Table 27-8. No. of Words in a Page and No. of Pages in the EEPROM
Device
EEPROM Size
512bytes
Page Size
4 bytes
PCWORD No. of Pages PCPAGE EEAMSB
ATmega164P-B
ATmega324P-B
ATmega644P-B
EEA[1:0]
EEA[1:0]
EEA[2:0]
128
256
256
EEA[8:2]
EEA[9:2]
EEA[10:2]
8
9
1Kbytes
4 bytes
2Kbytes
8 bytes
10
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27.6 Parallel Programming Parameters, Pin Mapping, and Commands
This section describes how to parallel program and verify flash program memory, EEPROM
data memory, memory lock bits, and fuse bits in the Atmel ATmega164P-B/324P-B/644P-B. Pulses are assumed to be at
least 250ns unless otherwise noted.
27.6.1 Signal Names
In this section, some pins of the Atmel ATmega164P-B/324P-B/644P-B are referenced by signal names describing their
functionality during parallel programming, see Figure 27-1 and Figure 27-9 on page 259. Pins not described in the following
table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding is shown in
Table 27-12 on page 260.
When pulsing WR or OE, the command loaded determines the action executed. The different commands are shown in
Table 27-13 on page 260.
Figure 27-1. Parallel Programming(1)
+ 5V
RDY/BSY
OE
PD1
PD2
PD3
PD4
PD5
PD6
PD7
VCC
+ 5V
WR
AVCC
BS1
XA0
PB7 to PB0
DATA
XA1
PAGEL
+12V
BS2
RESET
PA0
XTAL1
GND
Note:
1. Unused pins should be left floating.
Table 27-9. Pin Name Mapping
Signal Name in
Programming Mode
Pin Name
I/O
Function
0: Device is busy programming, 1: Device is ready for new
command.
RDY/BSY
PD1
O
OE
WR
PD2
PD3
PD4
PD5
PD6
PD7
PA0
I
Output enable (active low).
Write pulse (active low).
Byte select 1.
I
BS1
I
XA0
I
XTAL action bit 0
XA1
I
I
XTAL action bit 1
PAGEL
BS2
Program memory and EEPROM data page load.
Byte select 2.
I
DATA
PB7-0
I/O
Bi-directional data bus (output when OE is low).
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Table 27-10. BS2 and BS1 Encoding
Flash / EEPROM
Address
Flash Data Loading /
Reading
Reading Fuse and
Lock Bits
BS2
BS1
Fuse Programming
Low byte
0
0
1
1
0
1
0
1
Low byte
High byte
Low byte
High byte
Reserved
Reserved
Fuse low byte
Lock bits
High byte
Extended high byte
Reserved
Extended byte
Reserved
Extended fuse byte
Fuse high byte
,
Table 27-11. Pin Values Used to Enter Programming Mode
Pin
PAGEL
XA1
Symbol
Value
Prog_enable[3]
Prog_enable[2]
Prog_enable[1]
Prog_enable[0]
0
0
0
0
XA0
BS1
Table 27-12. XA1 and XA0 Encoding
XA1
XA0
Action when XTAL1 is Pulsed
Load flash or EEPROM address (high or low address byte determined by BS2 and
BS1)
0
0
0
1
1
1
0
1
Load data (high or low data byte for flash determined by BS1)
Load command
No action, idle
Table 27-13. Command Byte Bit Encoding
Command Byte
1000 0000
0100 0000
0010 0000
0001 0000
0001 0001
0000 1000
0000 0100
0000 0010
0000 0011
Command Executed
Chip erase
Write fuse bits
Write lock bits
Write flash
Write EEPROM
Read signature bytes and calibration byte
Read fuse and lock bits
Read flash
Read EEPROM
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27.7 Parallel Programming
27.7.1 Enter Programming Mode
The following algorithm puts the device in parallel programming mode:
1. Apply 4.5 - 5.5V between VCC and GND.
2. Set RESET to “0” and toggle XTAL1 at least six times.
3. Set the prog_enable pins listed in Table 27-11 on page 260 to “0000” and wait at least 100ns.
4. Apply 11.5 - 12.5V to RESET. Any activity on prog_enable pins within 100ns after +12V has been applied to
RESET, will cause the device to fail entering programming mode.
5. Wait at least 50µs before sending a new command.
27.7.2 Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient programming, the following
should be considered.
●
●
The command needs only be loaded once when writing or reading multiple memory locations.
Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the EESAVE fuse is programmed)
and flash after a chip erase.
●
Address high byte needs only be loaded before programming or reading a new 256 word window in flash or 256 byte
EEPROM. This consideration also applies to signature bytes reading.
27.7.3 Chip Erase
The chip erase will erase the flash and EEPROM(1) memories plus lock bits. The lock bits are not reset until the program
memory has been completely erased. The fuse bits are not changed. A chip erase must be performed before the flash
and/or EEPROM are reprogrammed.
Note:
1. The EEPRPOM memory is preserved during chip erase if the EESAVE fuse is programmed.
Load command “chip erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for chip erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the chip erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.
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27.7.4 Programming the Flash
The flash is organized in pages, see Table 27-7 on page 258. When programming the flash, the program data is latched into
a page buffer. This allows one page of program data to be programmed simultaneously. The following procedure describes
how to program the entire flash memory:
A. Load command “write flash”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for write flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load address low byte (address bits 7..0)
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS2, BS1 to “00”. This selects the address low byte.
3. Set DATA = address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load data low byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load data high byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch data
1. Set BS1 to “1”. This selects high data byte.
2. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 27-3 on page 263 for signal waveforms)
F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded.
While the lower bits in the address are mapped to words within the page, the higher bits address the pages within the
FLASH. This is illustrated in Figure 27-2 on page 263. Note that if less than eight bits are required to address words in the
page (Page size < 256), the most significant bit(s) in the address low byte are used to address the page when performing a
page write.
G. Load address high byte (address bits15..8)
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS2, BS1 to “01”. This selects the address high byte.
3. Set DATA = address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
H. Load address extended high byte (address bits 23..16)
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS2, BS1 to “10”. This selects the address extended high byte.
3. Set DATA = address extended high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
I. Program page
1. Set BS2, BS1 to “00”
2. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY goes low.
3. Wait until RDY/BSY goes high (See Figure 27-3 on page 263 for signal waveforms).
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J. Repeat B through I until the entire flash is programmed or until all data has been programmed.
K. End page programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are reset.
Figure 27-2. Addressing the Flash Which is Organized in Pages(1)
PCMSB
PAGEMSB
PCWORD
PROGRAM
COUNTER
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN PAGE
Program Memory
Page
Page
Instructions Word
PCWORD [PAGEMSB : 0]
00
01
02
PAGEEND
Note:
1. PCPAGE and PCWORD are listed in Table 27-7 on page 258.
Figure 27-3. Programming the Flash Waveforms(1)
F
A
B
C
D
E
B
C
D
E
G
H
I
0x10
ADDR. LOW DATA LOW DATA HIGH
XX
ADDR. LOW DATA LOW DATA HIGH
XX
ADDR. HIGH ADDR.EXT.H
XX
DATA
XA1
XA0
BS1
BS2
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
Note:
1. “XX” is don’t care. The letters refer to the programming description above.
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27.7.5 Programming the EEPROM
The EEPROM is organized in pages, see Table 27-8 on page 258. When programming the EEPROM, the program data is
latched into a page buffer. This allows one page of data to be programmed simultaneously. The programming algorithm for
the EEPROM data memory is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262 for details on
command, address and data loading):
1. A: Load command “0001 0001”.
2. G: Load address high byte (0x00 - 0xFF).
3. B: Load address low byte (0x00 - 0xFF).
4. C: Load data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS2, BS1 to “00”.
2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY goes low.
3. Wait until to RDY/BSY goes high before programming the next page (See Figure 27-4 for signal waveforms).
Figure 27-4. Programming the EEPROM Waveforms
K
A
G
B
C
E
B
C
E
L
DATA
XA1
0x11
ADDR. HIGH ADDR. LOW
DATA
XX
ADDR. LOW
DATA
XX
XA0
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
BS2
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27.7.6 Reading the Flash
The algorithm for reading the flash memory is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262 for
details on command and address loading):
1. A: Load command “0000 0010”.
2. H: Load address extended byte (0x00- 0xFF).
3. G: Load address high byte (0x00 - 0xFF).
4. B: Load address low byte (0x00 - 0xFF).
5. Set OE to “0”, and BS1 to “0”. The flash word low byte can now be read at DATA.
6. Set BS to “1”. The flash word high byte can now be read at DATA.
7. Set OE to “1”.
27.7.7 Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262
for details on command and address loading):
1. A: Load command “0000 0011”.
2. G: Load address high byte (0x00 - 0xFF).
3. B: Load address low byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM data byte can now be read at DATA.
5. Set OE to “1”.
27.7.8 Programming the Fuse Low Bits
The algorithm for programming the fuse low bits is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262
for details on command and data loading):
1. A: Load command “0100 0000”.
2. C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
27.7.9 Programming the Fuse High Bits
The algorithm for programming the fuse high bits is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262
for details on command and data loading):
1. A: Load command “0100 0000”.
2. C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.
3. Set BS2, BS1 to “01”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS2, BS1 to “00”. This selects low data byte.
27.7.10 Programming the Extended Fuse Bits
The algorithm for programming the extended fuse bits is as follows (refer to 27.7.4 “Programming the Flash” on page 262 for
details on command and data loading):
1. 1. A: Load command “0100 0000”.
2. 2. C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.
3. 3. Set BS2, BS1 to “10”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2, BS1 to “00”. This selects low data byte.
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Figure 27-5. Programming the FUSES Waveforms
Write Fuse Low byte
Write Fuse High byte
XX
Write Extended Fuse byte
A
C
A
C
A
C
DATA
XA1
XA0
BS1
0x40
DATA
XX
0x40
DATA
0x40
DATA
XX
BS2
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
27.7.11 Programming the Lock Bits
The algorithm for programming the lock bits is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262 for
details on command and data loading):
1. A: Load command “0010 0000”.
2. C: Load data low byte. Bit n = “0” programs the lock bit. If LB mode 3 is programmed (LB1 and LB2 is
programmed), it is not possible to program the boot lock bits by any external programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The lock bits can only be cleared by executing chip erase.
27.7.12 Reading the Fuse and Lock Bits
The algorithm for reading the fuse and lock bits is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262
for details on command loading):
1. A: Load command “0000 0100”.
2. Set OE to “0”, and BS2, BS1 to “00”. The status of the fuse low bits can now be read at DATA (“0” means
programmed).
3. Set OE to “0”, and BS2, BS1 to “11”. The status of the fuse high bits can now be read at DATA (“0” means
programmed).
4. Set OE to “0”, and BS2, BS1 to “10”. The status of the extended fuse bits can now be read at DATA (“0” means
programmed).
5. Set OE to “0”, and BS2, BS1 to “01”. The status of the lock bits can now be read at DATA (“0” means
programmed).
6. Set OE to “1”.
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Figure 27-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
Fuse Low Byte
0
0
1
Extended Fuse Byte
Lock Bits
1
0
DATA
BS2
BS1
Fuse High Byte
1
BS2
27.7.13 Reading the Signature Bytes
The algorithm for reading the signature bytes is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262 for
details on command and address loading):
1. A: Load command “0000 1000”.
2. B: Load address low byte (0x00 - 0x02).
3. Set OE to “0”, and BS to “0”. The selected signature byte can now be read at DATA.
4. Set OE to “1”.
27.7.14 Reading the Calibration Byte
The algorithm for reading the calibration byte is as follows (refer to Section 27.7.4 “Programming the Flash” on page 262 for
details on command and address loading):
1. A: Load command “0000 1000”.
2. B: Load address low byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The calibration byte can now be read at DATA.
4. Set OE to “1”.
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27.7.15 Parallel Programming Characteristics
Table 27-14. Parallel Programming Characteristics, VCC = 5V ±10%
Parameter
Symbol
VPP
Min
Typ.
Max
12.5
250
Unit
V
Programming enable voltage
Programming enable current
Data and control valid before XTAL1 high
XTAL1 low to XTAL1 high
XTAL1 pulse width high
11.5
IPP
µA
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
µs
ms
ms
ns
ns
ns
ns
tDVXH
tXLXH
tXHXL
tXLDX
tXLWL
tXLPH
tPLXH
tBVPH
tPHPL
tPLBX
tWLBX
tPLWL
tBVWL
tWLWH
tWLRL
tWLRH
tWLRH_CE
tXLOL
tBVDV
tOLDV
tOHDZ
67
200
150
67
0
Data and control hold after XTAL1 low
XTAL1 low to WR low
XTAL1 low to PAGEL high
PAGEL low to XTAL1 high
BS1 valid before PAGEL high
PAGEL pulse width high
0
150
67
150
67
67
67
67
150
0
BS1 hold after PAGEL low
BS2/1 hold after WR low
PAGEL low to WR low
BS2/1 valid to WR low
WR pulse width low
WR low to RDY/BSY low
1
4.5
9
WR low to RDY/BSY high(1)
WR low to RDY/BSY high for chip erase(2)
XTAL1 low to OE low
3.7
7.5
0
BS1 valid to DATA valid
0
250
250
250
OE low to DATA valid
OE high to DATA tri-stated
Notes: 1. tWLRH is valid for the write flash, Write EEPROM, write fuse bits and write lock bits commands.
2. WLRH_CE is valid for the chip erase command.
t
Figure 27-7. Parallel Programming Timing, Including some General Timing Requirements
tXLWL
XTAL1
tXHXL
tDVXH
tXLDX
Data and Control
(DATA, XA0/1, BS1, BS2)
tBVPH
tPLBX
tBVWL
tWLBX
PAGEL
WR
tPHPL
tWLWH
tPLWL
tWLRL
RDY/BSY
tWLRH
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Figure 27-8. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)
Load Address
(Low Byte)
Load Data
(Low Byte)
Load Data
(High Byte)
Load Address
(Low Byte)
Load Data
tXLPH
tXLXH
tPLXH
XTAL1
BS1
PAGEL
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1
Note:
The timing requirements shown in Figure 27-7 on page 268 (i.e., tDVXH, tXHXL, and tXLDX) also apply to loading
operation.
Figure 27-9. Parallel Programming Timing, Reading Sequence (within the Same Page) with Timing Requirements(1)
Load Address
(Low Byte)
Read Data
(Low Byte)
Read Data
(High Byte)
Load Address
(Low Byte)
tXLOL
XTAL1
BS1
tBVDV
tOLDV
OE
tOHDZ
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1
Note:
1. The timing requirements shown in Table 27-7 on page 268 (i.e., tDVXH, tXHXL, and tXLDX) also apply to reading
operation.
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27.8 Serial Downloading
Both the flash and EEPROM memory arrays can be programmed using a serial programming bus while RESET is pulled to
GND. The serial programming interface consists of pins SCK, MOSI (input) and MISO (output). After RESET is set low, the
programming enable instruction needs to be executed first before program/erase operations can be executed. NOTE, in
Table 27-15, the pin mapping for serial programming is listed. Not all packages use the SPI pins dedicated for the internal
serial peripheral interface - SPI.
27.8.1 Serial Programming Pin Mapping
Table 27-15. Pin Mapping Serial Programming
Symbol
MOSI
MISO
SCK
Pins (PDIP-40)
Pins (TQFP/MLF-44)
I/O
Description
Serial data in
Serial data out
Serial clock
PB5
PB6
PB7
PB5
PB6
PB7
I
O
I
Figure 27-10. Serial Programming and Verify(1)
+ 2.7V to 5.5V
VCC
+ 2.7V to 5.5V(2)
MOSI
MISO
SCK
AVCC
XTAL1
RESET
GND
Notes: 1. If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the XTAL1 pin.
2. VCC – 0.3V < AVCC < VCC + 0.3V, however, AVCC should always be within 2.7 to 5.5V
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the serial mode
ONLY) and there is no need to first execute the chip erase instruction. The chip erase operation turns the content of every
memory location in both the program and EEPROM arrays into 0xFF.
Depending on CKSEL fuses, a valid clock must be present. The minimum low and high periods for the serial clock (SCK)
input are defined as follows:
Low:
> 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck ≥ 12MHz
High:
> 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck ≥ 12MHz
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27.8.2 Serial Programming Algorithm
When writing serial data to the Atmel® ATmega164P-B/324P-B/644P-B, data is clocked on the rising edge of SCK.
When reading data from the Atmel ATmega164P-B/324P-B/644P-B, data is clocked on the falling edge of SCK.
See Figure 27-12 on page 273 for timing details.
To program and verify the ATmega164P-B/324P-B/644P-B in the serial programming mode, the following sequence is
recommended (see four byte instruction formats in Table 27-17 on page 272):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some systems, the programmer can
not guarantee that SCK is held low during power-up. In this case, RESET must be given a positive pulse of at
least two CPU clock cycles duration after SCK has been set to “0”.
2. Wait for at least 20ms and enable serial programming by sending the programming enable serial instruction to pin
MOSI.
3. The serial programming instructions will not work if the communication is out of synchronization. When in sync.
the second byte (0x53), will echo back when issuing the third byte of the programming enable instruction. Whether
the echo is correct or not, all four bytes of the instruction must be transmitted. If the 0x53 did not echo back, give
RESET a positive pulse and issue a new programming enable command.
4. The flash is programmed one page at a time. The memory page is loaded one byte at a time by supplying the 7
LSB of the address and data together with the load program memory page instruction. To ensure correct loading
of the page, the data low byte must be loaded before data high byte is applied for a given address. The program
memory page is stored by loading the write program memory page instruction with the address lines 15.8. Before
issuing this command, make sure the instruction load extended address byte has been used to define the MSB of
the address. The extended address byte is stored until the command is re-issued, i.e., the command needs only
be issued for the first page, and when crossing the 64KWord boundary. If polling (RDY/BSY) is not used, the user
must wait at least tWD_FLASH before issuing the next page. (See Table 27-16 on page 271.) Accessing the serial
programming interface before the flash write operation completes can result in incorrect programming.
5. The EEPROM array is programmed one byte at a time by supplying the address and data together with the
appropriate write instruction. An EEPROM memory location is first automatically erased before new data is
written. If polling is not used, the user must wait at least tWD_EEPROM before issuing the next byte.
(See Table 27-16 on page 271.) In a chip erased device, no 0xFFs in the data file(s) need to be programmed.
6. Any memory location can be verified by using the read instruction which returns the content at the selected
address at serial output MISO. When reading the flash memory, use the instruction load extended address byte to
define the upper address byte, which is not included in the read program memory instruction. The extended
address byte is stored until the command is re-issued, i.e., the command needs only be issued for the first page,
and when crossing the 64KWord boundary.
7. At the end of the programming session, RESET can be set high to commence normal operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
Table 27-16. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol
tWD_FLASH
tWD_EEPROM
tWD_ERASE
Minimum Wait Delay
4.5ms
3.6ms
9.0ms
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27.9 Serial Programming Instruction set
Table 27-17 and Figure 27-11 on page 273 describes the instruction set.
Table 27-17. Serial Programming Instruction Set (Hexadecimal values)
Instruction Format
Instruction/Operation
Byte 1
$AC
Byte 2
Byte 3
$00
Byte4
$00
Programming enable
$53
$80
$00
Chip erase (program memory/EEPROM)
Poll RDY/BSY
$AC
$00
$00
$F0
$00
data byte out
Load instructions
Load extended address byte(1)
Load program memory page, high byte
Load program memory page, low byte
$4D
$48
$40
$00
$00
$00
Extended adr
adr LSB
$00
high data byte in
low data byte in
adr LSB
Load EEPROM memory Page (page
access)
$C1
$00
0000 000aa
data byte in
Read instructions
Read program memory, high byte
Read program memory, low byte
Read EEPROM memory
Read lock bits
$28
$20
$A0
$58
$30
$50
$58
$50
$38
adr MSB
adr MSB
0000 00aa
$00
adr LSB
adr LSB
aaaa aaaa
$00
high data byte out
low data byte out
data byte out
data byte out
data byte out
data byte out
data byte out
data byte out
data byte out
Read signature byte
$00
0000 000aa
$00
Read fuse bits
$00
Read fuse high bits
$08
$00
Read extended fuse its
Read calibration byte
Write instructions(6)
$08
$00
$00
$00
Write program memory page
Write EEPROM memory
$4C
$C0
adr MSB
adr LSB
$00
0000 00aa
aaaa aaaa
data byte in
Write EEPROM memory page (page
access)
$C2
0000 00aa
aaaa aa00
$00
Write lock bits
$AC
$AC
$AC
$AC
$E0
$A0
$A8
$A4
$00
$00
$00
$00
data byte in
data byte in
data byte in
data byte in
Write fuse bits
Write fuse high bits
Write extended fuse bits
Notes: 1. Not all instructions are applicable for all parts.
2. a = address.
3. Bits are programmed ‘0’, unprogrammed ‘1’.
4. To ensure future compatibility, unused fuses and lock bits should be unprogrammed (‘1’).
5. Refer to the corresponding section for fuse and lock bits, calibration and signature bytes and page size.
6. Instructions accessing program memory use a word address. This address may be random within the page
range.
7. See http://www.atmel.com/avr for application notes regarding programming and programmers.
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If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until this bit returns ‘0’ before the
next instruction is carried out.
Within the same page, the low data byte must be loaded prior to the high data byte.
After data is loaded to the page buffer, program the EEPROM page, see Figure 27-11 on page 273.
Figure 27-11. Serial Programming Instruction Example
Serial Programming Instruction
Load Program Memory Page (High/Low Byte)/
Load EEPROM Memory Page (page access)
Write Program Memory Page /
Write EEPROM Memory Page
Byte 1
Byte 2
Byte 3
Byte 4
Byte 1
Byte 2
Byte 3
Byte 4
Adr MBS
Adr LBS
Adr MBS
Adr LBS
Bit 15 B
0
Bit 15 B
0
Page Buffer
Page Offset
Page 0
Page 1
Page 2
Page Number
Page N-1
Program Memory /
EEPROM Memory
27.9.1 Serial Programming Characteristics
For characteristics of the serial programming module See Section 28.7 “SPI Timing Characteristics” on page 292.
Figure 27-12. Serial Programming Waveforms
SERIAL DATA INPUT
MSB
LSB
LSB
(MOSI)
SERIAL DATA OUTPUT
(MISO)
MSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
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27.10 Programming via the JTAG Interface
Programming through the JTAG interface requires control of the four JTAG specific pins: TCK, TMS, TDI, and TDO. Control
of the reset and clock pins is not required.
To be able to use the JTAG interface, the JTAGEN fuse must be programmed. The device is default shipped with the fuse
programmed. In addition, the JTD bit in MCUCR must be cleared. Alternatively, if the JTD bit is set, the external reset can be
forced low. Then, the JTD bit will be cleared after two chip clocks, and the JTAG pins are available for programming. This
provides a means of using the JTAG pins as normal port pins in running mode while still allowing in-system programming via
the JTAG interface. Note that this technique can not be used when using the JTAG pins for boundary-scan or on-chip debug.
In these cases the JTAG pins must be dedicated for this purpose.
During programming the clock frequency of the TCK Input must be less than the maximum frequency of the chip. The
system clock prescaler can not be used to divide the TCK Clock Input into a sufficiently low frequency.
As a definition in this datasheet, the LSB is shifted in and out first of all shift registers.
27.10.1 Programming Specific JTAG Instructions
The instruction register is 4-bit wide, supporting up to 16 instructions. The JTAG instructions useful for programming are
listed below.
The OPCODE for each instruction is shown behind the instruction name in hex format. The text describes which data
register is selected as path between TDI and TDO for each instruction.
The run-test/Idle state of the TAP controller is used to generate internal clocks. It can also be used as an idle state between
JTAG sequences. The state machine sequence for changing the instruction word is shown in Figure 27-13 on page 275.
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Figure 27-13. State Machine Sequence for Changing the Instruction Word
1
Test Logic Reset
0
1
1
1
0
Run Test/Idle
Select DR Scan
0
Select IR Scan
0
1
1
Capture DR
0
Capture IR
0
Shift DR
1
0
Shift IR
1
0
1
1
Exit1 DR
0
Exit1 IR
0
Pause DR
1
0
Pause IR
1
0
0
0
Exit2 DR
1
Exit2 IR
1
Update DR
Update IR
1
0
1
0
27.10.2 AVR_RESET (0xC)
The AVR® specific public JTAG instruction for setting the AVR device in the reset mode or taking the device out from the
reset mode. The TAP controller is not reset by this instruction. The one bit reset register is selected as data register. Note
that the reset will be active as long as there is a logic “one” in the reset chain. The output from this chain is not latched.
The active states are:
●
Shift-DR: The reset register is shifted by the TCK input.
27.10.3 PROG_ENABLE (0x4)
The AVR specific public JTAG instruction for enabling programming via the JTAG port. The 16-bit programming enable
register is selected as data register. The active states are the following:
●
●
Shift-DR: The programming enable signature is shifted into the data register.
Update-DR: The programming enable signature is compared to the correct value, and programming mode is entered
if the signature is valid.
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27.10.4 PROG_COMMANDS (0x5)
The AVR® specific public JTAG instruction for entering programming commands via the JTAG port. The 15-bit programming
command register is selected as data register. The active states are the following:
●
●
Capture-DR: The result of the previous command is loaded into the data register.
Shift-DR: The data register is shifted by the TCK input, shifting out the result of the previous command and shifting in
the new command.
●
●
Update-DR: The programming command is applied to the flash inputs
Run-test/Idle: One clock cycle is generated, executing the applied command
27.10.5 PROG_PAGELOAD (0x6)
The AVR specific public JTAG instruction to directly load the flash data page via the JTAG port. An 8-bit flash data byte
register is selected as the data register. This is physically the 8 LSBs of the programming command register. The active
states are the following:
●
●
Shift-DR: The flash data byte register is shifted by the TCK input.
Update-DR: The content of the flash data byte register is copied into a temporary register. A write sequence is
initiated that within 11 TCK cycles loads the content of the temporary register into the flash page buffer. The AVR
automatically alternates between writing the low and the high byte for each new update-DR state, starting with the low
byte for the first update-DR encountered after entering the PROG_PAGELOAD command. The program counter is
pre-incremented before writing the low byte, except for the first written byte. This ensures that the first data is written
to the address set up by PROG_COMMANDS, and loading the last location in the page buffer does not make the
program counter increment into the next page.
27.10.6 PROG_PAGEREAD (0x7)
The AVR specific public JTAG instruction to directly capture the flash content via the JTAG port. An 8-bit flash data byte
register is selected as the data register. This is physically the 8 LSBs of the programming command register. The active
states are the following:
●
Capture-DR: The content of the selected flash byte is captured into the flash data byte register. The AVR
automatically alternates between reading the low and the high byte for each new capture-DR state, starting with the
low byte for the first capture-DR encountered after entering the PROG_PAGEREAD command. The program counter
is post-incremented after reading each high byte, including the first read byte. This ensures that the first data is
captured from the first address set up by PROG_COMMANDS, and reading the last location in the page makes the
program counter increment into the next page.
●
Shift-DR: The flash data byte register is shifted by the TCK input.
27.10.7 Data Registers
The data registers are selected by the JTAG instruction registers described in section Section 27.10.1 “Programming
Specific JTAG Instructions” on page 274. The data registers relevant for programming operations are:
●
●
●
●
Reset register
Programming enable register
Programming command register
Flash data byte register
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27.10.8 Reset Register
The reset register is a test data register used to reset the part during programming. It is required to reset the part before
entering programming mode.
A high value in the reset register corresponds to pulling the external reset low. The part is reset as long as there is a high
value present in the reset register. Depending on the fuse settings for the clock options, the part will remain reset for a reset
time-out period (refer to Section 9.2 “Clock Sources” on page 24) after releasing the reset register. The output from this data
register is not latched, so the reset will take place immediately, as shown in Figure 25-2 on page 232.
27.10.9 Programming Enable Register
The programming enable register is a 16-bit register. The contents of this register is compared to the programming enable
signature, binary code 0b1010_0011_0111_0000. When the contents of the register is equal to the programming enable
signature, programming via the JTAG port is enabled. The register is reset to 0 on power-on reset, and should always be
reset when leaving programming mode.
Figure 27-14. Programming Enable Register
TDI
0xA370
D
A
T
A
D
Q
Programming Enable
=
ClockDR and PROG_ENABLE
TDO
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27.10.10 Programming Command Register
The programming command register is a 15-bit register. This register is used to serially shift in programming commands, and
to serially shift out the result of the previous command, if any. The JTAG programming instruction Set is shown in
Table 27-18 on page 279. The state sequence when shifting in the programming commands is illustrated in
Figure 27-16 on page 282.
Figure 27-15. Programming Command Register
TDI
S
T
R
O
B
E
S
Flash
A
D
EEPROM
Fuses
D
Lock Bits
R
E
S
S
/
D
A
T
A
TDO
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Table 27-18. JTAG Programming Instruction
Set a = address high bits, b = address low bits, c = address extended bits, H = 0 - Low byte, 1 - High byte,
o = data out, i = data in, x = don’t care
Instruction
TDI Sequence
TDO Sequence
Notes
0100011_10000000
0110001_10000000
0110011_10000000
0110011_10000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
1a. Chip erase
1b. Poll for chip erase complete
2a. Enter flash write
0110011_10000000
0100011_00010000
0001011_cccccccc
0000111_aaaaaaaa
0000011_bbbbbbbb
0010011_iiiiiiii
xxxxxox_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(2)
2b. Load address extended high byte
2c. Load address high byte
2d. Load address low byte
2e. Load data low byte
(10)
2f. Load data high byte
0010111_iiiiiiii
0110111_00000000
1110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
2g. Latch data
(1)
(1)
0110111_00000000
0110101_00000000
0110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
2h. Write flash page
2i. Poll for page write complete
3a. Enter flash read
0110111_00000000
0100011_00000010
0001011_cccccccc
0000111_aaaaaaaa
0000011_bbbbbbbb
xxxxxox_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(2)
3b. Load address extended high byte
3c. Load address high byte
3d. Load address low byte
(10)
0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
Low byte
High byte
3e. Read data low and high byte
4a. Enter EEPROM write
4b. Load address high byte
4c. Load address low byte
4d. Load data byte
0100011_00010001
0000111_aaaaaaaa
0000011_bbbbbbbb
0010011_iiiiiiii
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(10)
Notes: 1. This command sequence is not required if the seven MSB are correctly set by the previous command
sequence (which is normally the case).
2. Repeat until o = “1”.
3. Set bits to “0” to program the corresponding Fuse, “1” to unprogram the fuse.
4. Set bits to “0” to program the corresponding lock bit, “1” to leave the lock bit unchanged.
5. “0” = programmed, “1” = unprogrammed.
6. The bit mapping for fuses extended byte is listed in Table 27-3 on page 256
7. The bit mapping for fuses high byte is listed in Table 27-4 on page 257
8. The bit mapping for fuses low byte is listed in Table 27-5 on page 257
9. The bit mapping for lock bits byte is listed in Table 27-1 on page 255
10. Address bits exceeding PCMSB and EEAMSB (Table 27-7 on page 258 and Table 27-8 on page 258) are
don’t care
11. All TDI and TDO sequences are represented by binary digits (0b...).
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Table 27-18. JTAG Programming Instruction (Continued)
Set a = address high bits, b = address low bits, c = address extended bits, H = 0 - Low byte, 1 - High byte,
o = data out, i = data in, x = don’t care
Instruction
TDI Sequence
TDO Sequence
Notes
0110111_00000000
1110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
4e. Latch data
(1)
0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
4f. Write EEPROM page
(1)
4g. Poll for page write complete
5a. Enter EEPROM read
0110011_00000000
0100011_00000011
0000111_aaaaaaaa
0000011_bbbbbbbb
xxxxxox_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(2)
5b. Load address high byte
5c. Load address Low Byte
(10)
0110011_bbbbbbbb
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
5d. Read data byte
6a. Enter fuse write
6b. Load data low byte(6)
0100011_01000000
0010011_iiiiiiii
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(3)
(1)
0111011_00000000
0111001_00000000
0111011_00000000
0111011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
6c. Write fuse extended byte
6d. Poll for fuse write complete
6e. Load data low byte(7)
0110111_00000000
0010011_iiiiiiii
xxxxxox_xxxxxxxx
xxxxxxx_xxxxxxxx
(2)
(3)
0110111_00000000
0110101_00000000
0110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
6f. Write fuse high byte
(1)
6g. Poll for fuse write complete
6h. Load data low byte(7)
0110111_00000000
0010011_iiiiiiii
xxxxxox_xxxxxxxx
xxxxxxx_xxxxxxxx
(2)
(3)
0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
6i. Write fuse low byte
(1)
(2)
6j. Poll for fuse write complete
0110011_00000000
xxxxxox_xxxxxxxx
Notes: 1. This command sequence is not required if the seven MSB are correctly set by the previous command
sequence (which is normally the case).
2. Repeat until o = “1”.
3. Set bits to “0” to program the corresponding Fuse, “1” to unprogram the fuse.
4. Set bits to “0” to program the corresponding lock bit, “1” to leave the lock bit unchanged.
5. “0” = programmed, “1” = unprogrammed.
6. The bit mapping for fuses extended byte is listed in Table 27-3 on page 256
7. The bit mapping for fuses high byte is listed in Table 27-4 on page 257
8. The bit mapping for fuses low byte is listed in Table 27-5 on page 257
9. The bit mapping for lock bits byte is listed in Table 27-1 on page 255
10. Address bits exceeding PCMSB and EEAMSB (Table 27-7 on page 258 and Table 27-8 on page 258) are
don’t care
11. All TDI and TDO sequences are represented by binary digits (0b...).
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Table 27-18. JTAG Programming Instruction (Continued)
Set a = address high bits, b = address low bits, c = address extended bits, H = 0 - Low byte, 1 - High byte,
o = data out, i = data in, x = don’t care
Instruction
TDI Sequence
0100011_00100000
0010011_11iiiiii
TDO Sequence
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
Notes
7a. Enter lock bit write
7b. Load data byte(9)
(4)
0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
7c. Write lock bits
(1)
(2)
7d. Poll for lock bit write complete
8a. Enter fuse/lock bit read
0110011_00000000
0100011_00000100
xxxxxox_xxxxxxxx
xxxxxxx_xxxxxxxx
0111010_00000000
0111011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8b. Read extended fuse byte(6)
8c. Read fuse high byte(7)
8d. Read fuse low byte(8)
8e. Read lock bits(9)
0111110_00000000
0111111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxoooooo
(5)
0111010_00000000
0111110_00000000
0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
(5)
Fuse ext. byte
Fuse high byte
Fuse low byte lock
bits
8f. Read fuses and lock bits
9a. Enter signature byte read
9b. Load address byte
0100011_00001000
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
9c. Read signature byte
10a. Enter calibration byte read
10b. Load address byte
0100011_00001000
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
10c. Read calibration byte
0100011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
11a. Load no operation command
Notes: 1. This command sequence is not required if the seven MSB are correctly set by the previous command
sequence (which is normally the case).
2. Repeat until o = “1”.
3. Set bits to “0” to program the corresponding Fuse, “1” to unprogram the fuse.
4. Set bits to “0” to program the corresponding lock bit, “1” to leave the lock bit unchanged.
5. “0” = programmed, “1” = unprogrammed.
6. The bit mapping for fuses extended byte is listed in Table 27-3 on page 256
7. The bit mapping for fuses high byte is listed in Table 27-4 on page 257
8. The bit mapping for fuses low byte is listed in Table 27-5 on page 257
9. The bit mapping for lock bits byte is listed in Table 27-1 on page 255
10. Address bits exceeding PCMSB and EEAMSB (Table 27-7 on page 258 and Table 27-8 on page 258) are
don’t care
11. All TDI and TDO sequences are represented by binary digits (0b...).
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Figure 27-16. State Machine Sequence for Changing/Reading the Data Word
1
Test Logic Reset
0
1
1
1
0
Run Test/Idle
Select DR Scan
0
Select IR Scan
0
1
1
Capture DR
0
Capture IR
0
Shift DR
1
0
Shift IR
1
0
1
1
Exit1 DR
0
Exit1 IR
0
Pause DR
1
0
Pause IR
1
0
0
0
Exit2 DR
1
Exit2 IR
1
Update DR
Update IR
1
0
1
0
27.10.11 Flash Data Byte Register
The flash data byte register provides an efficient way to load the entire flash page buffer before executing page write, or to
read out/verify the content of the flash. A state machine sets up the control signals to the flash and senses the strobe signals
from the flash, thus only the data words need to be shifted in/out.
The flash data byte register actually consists of the 8-bit scan chain and a 8-bit temporary register. During page load, the
update-DR state copies the content of the scan chain over to the temporary register and initiates a write sequence that within
11 TCK cycles loads the content of the temporary register into the flash page buffer. The AVR® automatically alternates
between writing the low and the high byte for each new update-DR state, starting with the low byte for the first update-DR
encountered after entering the PROG_PAGELOAD command. The program counter is pre-incremented before writing the
low byte, except for the first written byte. This ensures that the first data is written to the address set up by
PROG_COMMANDS, and loading the last location in the page buffer does not make the program counter increment into the
next page.
During page read, the content of the selected flash byte is captured into the flash data byte register during the capture-DR
state. The AVR automatically alternates between reading the low and the high byte for each new capture-DR state, starting
with the low byte for the first capture-DR encountered after entering the PROG_PAGEREAD command. The program
counter is post-incremented after reading each high byte, including the first read byte. This ensures that the first data is
captured from the first address set up by PROG_COMMANDS, and reading the last location in the page makes the program
counter increment into the next page.
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Figure 27-17. Flash Data Byte Register
STROBES
ADDRESS
State
Machine
TDI
Flash
EEPROM
Fuses
Lock Bits
D
A
T
A
TDO
The state machine controlling the flash data byte register is clocked by TCK. During normal operation in which eight bits are
shifted for each flash byte, the clock cycles needed to navigate through the TAP controller automatically feeds the state
machine for the flash data byte register with sufficient number of clock pulses to complete its operation transparently for the
user. However, if too few bits are shifted between each update-DR state during page load, the TAP controller should stay in
the run-test/idle state for some TCK cycles to ensure that there are at least 11 TCK cycles between each update-DR state.
27.10.12 Programming Algorithm
All references below of type “1a”, “1b”, and so on, refer to Table 27-18 on page 279.
27.10.13 Entering Programming Mode
1. Enter JTAG instruction AVR_RESET and shift 1 in the reset register.
2. Enter instruction PROG_ENABLE and shift 0b1010_0011_0111_0000 in the programming enable register.
27.10.14 Leaving Programming Mode
1. Enter JTAG instruction PROG_COMMANDS.
2. Disable all programming instructions by using no operation instruction 11a.
3. Enter instruction PROG_ENABLE and shift 0b0000_0000_0000_0000 in the programming enable register.
4. Enter JTAG instruction AVR_RESET and shift 0 in the reset register.
27.10.15 Performing Chip Erase
1. Enter JTAG instruction PROG_COMMANDS.
2. Start chip erase using programming instruction 1a.
3. Poll for chip erase complete using programming instruction 1b, or wait for tWLRH_CE (refer to
Table 27-14 on page 268).
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27.10.16 Programming the Flash
Before programming the flash a chip erase must be performed, see Section 27.10.15 “Performing Chip Erase” on page 283.
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable flash write using programming instruction 2a.
3. Load address extended high byte using programming instruction 2b.
4. Load address high byte using programming instruction 2c.
5. Load address low byte using programming instruction 2d.
6. Load data using programming instructions 2e, 2f and 2g.
7. Repeat steps 5 and 6 for all instruction words in the page.
8. Write the page using programming instruction 2h.
9. Poll for flash write complete using programming instruction 2i, or wait for tWLRH (refer to Table 27-14 on page 268).
10. Repeat steps 3 to 9 until all data have been programmed.
A more efficient data transfer can be achieved using the PROG_PAGELOAD instruction:
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable flash write using programming instruction 2a.
3. Load the page address using programming instructions 2b, 2c and 2d. PCWORD (refer to Table 27-7 on page
258) is used to address within one page and must be written as 0.
4. Enter JTAG instruction PROG_PAGELOAD.
5. Load the entire page by shifting in all instruction words in the page byte-by-byte, starting with the LSB of the first
instruction in the page and ending with the MSB of the last instruction in the page. Use update-DR to copy the
contents of the flash data byte register into the flash page location and to auto-increment the program counter
before each new word.
6. Enter JTAG instruction PROG_COMMANDS.
7. Write the page using programming instruction 2h.
8. Poll for flash write complete using programming instruction 2i, or wait for tWLRH (refer to Table 27-14 on page 268).
9. Repeat steps 3 to 8 until all data have been programmed.
27.10.17 Reading the Flash
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable flash read using programming instruction 3a.
3. Load address using programming instructions 3b, 3c and 3d.
4. Read data using programming instruction 3e.
5. Repeat steps 3 and 4 until all data have been read.
A more efficient data transfer can be achieved using the PROG_PAGEREAD instruction:
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable flash read using programming instruction 3a.
3. Load the page address using programming instructions 3b, 3c and 3d. PCWORD (refer to
Table 27-7 on page 258) is used to address within one page and must be written as 0.
4. Enter JTAG instruction PROG_PAGEREAD.
5. Read the entire page (or flash) by shifting out all instruction words in the page (or flash), starting with the LSB of
the first instruction in the page (flash) and ending with the MSB of the last instruction in the page (flash). The
capture-DR state both captures the data from the flash, and also auto-increments the program counter after each
word is read. Note that capture-DR comes before the shift-DR state. Hence, the first byte which is shifted out con-
tains valid data.
6. Enter JTAG instruction PROG_COMMANDS.
7. Repeat steps 3 to 6 until all data have been read.
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27.10.18 Programming the EEPROM
Before programming the EEPROM a chip erase must be performed, See Section 27.10.15 “Performing Chip Erase” on page
283.
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM write using programming instruction 4a.
3. Load address high byte using programming instruction 4b.
4. Load address low byte using programming instruction 4c.
5. Load data using programming instructions 4d and 4e.
6. Repeat steps 4 and 5 for all data bytes in the page.
7. Write the data using programming instruction 4f.
8. Poll for EEPROM write complete using programming instruction 4g, or wait for tWLRH (refer to
Table 27-14 on page 268).
9. Repeat steps 3 to 8 until all data have been programmed.
Note that the PROG_PAGELOAD instruction can not be used when programming the EEPROM.
27.10.19 Reading the EEPROM
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM read using programming instruction 5a.
3. Load address using programming instructions 5b and 5c.
4. Read data using programming instruction 5d.
5. Repeat steps 3 and 4 until all data have been read.
Note that the PROG_PAGEREAD instruction can not be used when reading the EEPROM.
27.10.20 Programming the Fuses
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable fuse write using programming instruction 6a.
3. Load data high byte using programming instructions 6b. A bit value of “0” will program the corresponding fuse, a
“1” will unprogram the fuse.
4. Write fuse high byte using programming instruction 6c.
5. Poll for fuse write complete using programming instruction 6d, or wait for tWLRH (refer to Table 27-14 on page 268).
6. Load data low byte using programming instructions 6e. A “0” will program the fuse, a “1” will unprogram the fuse.
7. Write fuse low byte using programming instruction 6f.
8. Poll for fuse write complete using programming instruction 6g, or wait for tWLRH (refer to Table 27-14 on page 268).
27.10.21 Programming the Lock Bits
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable lock bit write using programming instruction 7a.
3. Load data using programming instructions 7b. A bit value of “0” will program the corresponding lock bit, a “1” will
leave the lock bit unchanged.
4. Write lock bits using programming instruction 7c.
5. Poll for lock bit write complete using programming instruction 7d, or wait for tWLRH (refer to Table 27-14 on page
268).
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27.10.22 Reading the Fuses and Lock Bits
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable fuse/lock bit read using programming instruction 8a.
3. To read all fuses and lock bits, use programming instruction 8e.
To only read fuse high byte, use programming instruction 8b.
To only read fuse low byte, use programming instruction 8c.
To only read lock bits, use programming instruction 8d.
27.10.23 Reading the Signature Bytes
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable signature byte read using programming instruction 9a.
3. Load address 0x00 using programming instruction 9b.
4. Read first signature byte using programming instruction 9c.
5. Repeat steps 3 and 4 with address 0x01 and address 0x02 to read the second and third signature bytes,
respectively.
27.10.24 Reading the Calibration Byte
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable calibration byte read using programming instruction 10a.
3. Load address 0x00 using programming instruction 10b.
4. Read the calibration byte using programming instruction 10c.
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28. Electrical Characteristics
28.1 Absolute Maximum Ratings*
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Parameters
Min.
–55
–65
Typ.
Max.
+125
+150
Unit
°C
Operating temperature
Storage temperature
°C
Voltage on any pin except RESET
with respect to ground to
–0.5
–0.5
VCC + 0.5
V
Voltage on RESET with respect to ground
Maximum operating voltage
DC current per I/O Pin
+13.0
6.0
V
V
40.0
200.0
±5.0(1)
±1.0
mA
mA
mA
mA
DC current VCC and GND pins
Injection current at VCC = 0V
Injection current at VCC = 5V
Note:
1. Maximum current per port = ±30mA
28.2 DC Characteristics
Table 28-1. TA = –40°C to 125°C, VCC = 2.7V to 5.5V (Unless otherwise Noted)
Parameters
Condition
Symbol
Min.
Typ.
Max.
Unit
Input low voltage, except
XTAL1 and reset pin
(1)
(1)
(1)
VCC = 2.7V – 5.5V
VIL
–0.5
0.3VCC
0.1VCC
0.2VCC
V
V
V
V
V
V
Input low voltage,
XTAL1 pin
VCC = 2.7V – 5.5V
VCC = 2.7V – 5.5V
VCC = 2.7V – 5.5V
VCC = 2.7V – 5.5V
VCC = 2.7V – 5.5V
VIL1
VIL2
VIH
–0.5
–0.5
Input low voltage, RESET
pin
Input high voltage, except
XTAL1 and RESET pins
(2)
(2)
(2)
0.6VCC
0.7VCC
0.9VCC
VCC + 0.5
VCC + 0.5
VCC + 0.5
Input high voltage, XTAL1
pin
VIH1
VIH2
Input high voltage, RESET
pin
Notes: 1. “Max” means the highest value where the pin is guaranteed to be read as low
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
1.) The sum of all IOL, for ports PB0-PB7, XTAL2, PD0-PD7 should not exceed 100mA.
2.) The sum of all IOL, for ports PA0-PA3, PC0-PC7 should not exceed 100mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current
greater than the listed test condition.
4. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
1.) The sum of all IOH, for ports PB0-PB7, XTAL2, PD0-PD7 should not exceed 100mA.
2.) The sum of all IOH, for ports PA0-PA3, PC0-PC7 should not exceed 100mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
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Table 28-1. TA = –40°C to 125°C, VCC = 2.7V to 5.5V (Unless otherwise Noted) (Continued)
Parameters
Condition
Symbol
Min.
Typ.
Max.
Unit
IOL = 20mA, VCC = 5V
IOL = 10mA, VCC = 3V
0.8
0.5
Output low voltage(3)
VOL
V
IOH = –20mA, VCC = 5V
IOH = –10mA, VCC = 3V
4.1
2.3
Output high voltage(4)
VOH
IIL
V
Input leakage
Current I/O pin
VCC = 5.5V, pin low
(absolute value)
1
1
µA
µA
Input leakage
Current I/O pin
VCC = 5.5V, pin high
(absolute value)
IIH
Reset pull-up resistor
I/O pin pull-up resistor
RRST
RPU
30
20
60
50
kΩ
kΩ
Analog comparator
Input offset voltage
VCC = 5V, 0.1VCC < Vin <
VCC – 100mV
VACIO
IACLK
tACID
<10
40
50
mV
nA
ns
Analog comparator
Input leakage current
VCC = 5V
Vin = VCC/2
–50
Analog comparator
Propagation delay
VCC = 2.7V
VCC = 4.0V
750
500
Notes: 1. “Max” means the highest value where the pin is guaranteed to be read as low
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
1.) The sum of all IOL, for ports PB0-PB7, XTAL2, PD0-PD7 should not exceed 100mA.
2.) The sum of all IOL, for ports PA0-PA3, PC0-PC7 should not exceed 100mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current
greater than the listed test condition.
4. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
1.) The sum of all IOH, for ports PB0-PB7, XTAL2, PD0-PD7 should not exceed 100mA.
2.) The sum of all IOH, for ports PA0-PA3, PC0-PC7 should not exceed 100mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
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Table 28-2. TA = –40°C to 125°C, VCC = 2.7V to 5.5V (Unless otherwise Noted)
Parameter
Condition
Symbol
Min.
Typ.(2)
Max.
Unit
Active 4MHz, VCC = 3V
1.4
2.75
mA
Active 8MHz, VCC = 5V
Active 16MHz, VCC = 5V
4.8
8.6
10
15
mA
mA
Power supply current(1)
Idle 4MHz, VCC = 3V
0.25
1.5
mA
Idle 8MHz, VCC = 5V
Idle 16MHz, VCC = 5V
1.0
1.9
3.0
4.0
mA
mA
ICC
Power-save mode(3)
Power-down mode(3)
32kHz TOSC enabled, VCC = 3V
0.6
µA
WDT enabled, VCC = 3V
WDT enabled, VCC = 5V
WDT disabled, VCC = 3V
WDT disabled, VCC = 5V
4.8
7.3
0.3
0.6
60
95
54
85
µA
µA
µA
µA
Notes: 1. All bits set in the Section 10.12.3 “PRR0 – Power Reduction Register 0” on page 39.
2. Typical values at 25°C. maximum values are test limits in production.
3. The current consumption values include input leakage current.
28.3 Speed Grades
Maximum frequency is depending on VCC. As shown in Figure 28-1, the maximum frequency versus VCC curve is linear
between 2.7V < VCC < 4.5V.
Figure 28-1. Maximum Frequency versus VCC, ATmega164P-B/324P-B/644P-B
16MHz
8MHz
Safe Operating Area
2.7V
4.5V
5.5V
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28.4 Clock Characteristics
Table 28-3. Calibration Accuracy of Internal RC Oscillator
Frequency
8.0MHz
8.0MHz
8.0MHz
8.0MHz
128KHz
VCC
Temperature
25°C
Calibration Accuracy
3V
±1.5%
±14%
±1.5%
±10%
±40%
Default 3V factory
calibration
2.7 - 5.5V(1)
–40°C / +125°C
25°C
5V
5V factory
calibration
4.5 - 5.5V(1)
2.7 - 5.5V(1)
–40°C / +125°C
–40°C / +125°C
Watchdog oscillator
Note:
1. Voltage range for Atmel® ATmega164P-B/324P-B/644P-B.
28.4.1 External Clock Drive Waveforms
Figure 28-2. External Clock Drive Waveforms
tCHCX
tCLCH
tCHCL
tCHCX
VIH1
VIL1
tCLCX
tCLCL
28.4.2 External Clock Drive
Table 28-4. External Clock Drive
VCC = 2.7 to 5.5V
Min. Max.
VCC = 4.5 to 5.5V
Parameter
Oscillator frequency
Clock period
High time
Symbol
1/tCLCL
tCLCL
Min.
0
Max.
Unit
MHz
ns
0
8
16
125
40
62.5
20
tCHCX
tCLCX
ns
Low time
40
20
ns
Rise time
tCLCH
1.6
1.6
0.5
0.5
µs
Fall time
tCHCL
µs
Change in period from one clock
cycle to the next
ΔtCLCL
2
2
%
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28.5 System and Reset Characteristics
Table 28-5. Reset, Brown-out and Internal Voltage Reference Characteristics
Parameter
Condition
Symbol
Min
1.1
Typ.
1.4
Max
1.6
Unit
V
Power-on reset threshold voltage (rising)
Power-on reset threshold voltage (falling)(1)
RESET pin threshold voltage
Minimum pulse width on RESET pin
Brown-out detector hysteresis
Min pulse width on brown-out reset
Bandgap reference voltage
VPOT
0.6
1.3
1.6
V
VRST
tRST
0.2VCC
2.5
0.9VCC
V
µs
mV
µs
V
VHYST
tBOD
VBG
80
2
VCC= 2.7V, TA = 25°C
VCC= 2.7V, TA = 25°C
0.98
1.1
40
1.22
70
Bandgap reference start-up time
tBG
µs
Note:
1. The power-on reset will not work unless the supply voltage has been below VPOT (falling).
Table 28-6. BODLEVEL Fuse Coding(1)
BODLEVEL 2:0 Fuses
Min VBOT
Typical VBOT
BOD disabled
Max VBOT
Unit
111
110
101
100
011
010
001
000
1.7
2.5
4.0
1.8
2.7
4.3
2.0
2.9
V
4.55
Reserved
Note:
1. VBOT may be below nominal minimum operating voltage for some devices. For devices where this is the case,
the device is tested down to VCC = VBOT during the production test. This guarantees that a brown-out reset will
occur before VCC drops to a voltage where correct operation of the microcontroller is no longer guaranteed.
The test is performed using BODLEVEL = 101 and BODLEVEL = 110.
28.6 External Interrupts Characteristics
Table 28-7. Asynchronous External Interrupt Characteristics
Parameter
Condition
Symbol
Min
Typ.
Max
Unit
Minimum pulse width for asynchronous external interrupt
tINT
50
ns
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28.7 SPI Timing Characteristics
See Figure 28-3 and Figure 28-4 on page 293 for details.
Table 28-8. SPI Timing Parameters
Description
Mode
Min
Typ.
Max
See Table 18-5 on
page 145
1
SCK period
Master
2
3
SCK high/low
Rise/fall time
Setup
Master
Master
Master
Master
Master
Master
Master
Slave
Slave
Slave
Slave
Slave
Slave
Slave
Slave
Slave
Slave
50% duty cycle
3.6
10
4
5
Hold
10
6
Out to SCK
SCK to out
SCK to out high
SS low to out
SCK period
SCK high/low(1)
Rise/fall time
Setup
0.5 × tsck
10
7
8
10
9
15
ns
10
11
12
13
14
15
16
17
4 × tck
2 × tck
1600
10
tck
Hold
SCK to out
SCK to SS high
SS high to tri-state
SS low to SCK
15
10
20
20
18
Note:
1. In SPI programming mode the minimum SCK high/low period is:
– 2 tCLCL for fCK < 12MHz
–3 tCLCL for fCK > 12MHz
Figure 28-3. SPI Interface Timing Requirements (Master Mode)
SS
6
1
SCK
(CPOL = 0)
2
2
SCK
(CPOL = 1)
4
5
3
MISO
MSB
...
...
LSB
(Data Input)
8
7
MOSI
(Data Output)
MSB
LSB
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Figure 28-4. SPI Interface Timing Requirements (Slave Mode)
SS
16
9
10
SCK
(CPOL = 0)
11
11
SCK
(CPOL = 1)
13
14
12
MOSI
MSB
...
...
LSB
(Data Input)
17
15
MISO
(Data Output)
MSB
LSB
X
28.8 2-wire Serial Interface Characteristics
Table 28-9 describes the requirements for devices connected to the 2-wire serial bus. The Atmel®
ATmega164P-B/324P-B/644P-B 2-wire serial interface meets or exceeds these requirements under the noted conditions.
Timing symbols refer to Figure 28-5 on page 294.
Table 28-9. 2-wire Serial Bus Requirements
Parameter
Condition
Symbol
VIL
Min
–0.5
Max
0.3 VCC
VCC + 0.5
–
Unit
V
Input low-voltage
Input high-voltage
VIH
0.7 VCC
V
(1)
(2)
Hysteresis of schmitt trigger inputs
Output low-voltage
Vhys
0.05 VCC
V
(1)
3mA sink current
10pF < Cb < 400pF(3)
VOL
0
0.4
V
(2)(3)
(2)(3)
Rise time for both SDA and SCL
Output fall time from VIHmin to VILmax
Spikes suppressed by input filter
Input current each I/O pin
Capacitance for each I/O pin
SCL clock frequency
tr(1)
20 + 0.1Cb
300
ns
ns
ns
µA
pF
kHz
(1)
tof
20 + 0.1Cb
250
50(2)
(1)
tSP
0
–10
–
0.1VCC < Vi < 0.9VCC
Ii
10
Ci(1)
10
fCK(4)> max(16fSCL, 250kHz)(5)
fSCL
0
400
Notes: 1. In ATmega164P-B/324P-B/644P-B, this parameter is characterized and not 100% tested.
2. Required only for fSCL > 100kHz.
3. Cb = capacitance of one bus line in pF.
4.
fCK = CPU clock frequency
5. This requirement applies to all ATmega164P-B/324P-B/644P-B two-wire serial interface operation. Other devices con-
nected to the two-wire serial bus need only obey the general fSCL requirement.
6. The actual low period generated by the ATmega164P-B/324P-B/644P-B two-wire serial interface is (1/fSCL – 2/fCK), thus
fCK must be greater than 6MHz for the low time requirement to be strictly met at fSCL = 100kHz.
7. The actual low period generated by the ATmega164P-B/324P-B/644P-B two-wire serial interface is
(1/fSCL – 2/fCK), thus the low time requirement will not be strictly met for fSCL > 308kHz when fCK = 8MHz. Still,
ATmega164P-B/324P-B/644P-B devices connected to the bus may communicate at full speed (400kHz) with other
ATmega164P-B/324P-B/644P-B devices, as well as any other device with a proper tLOW acceptance margin.
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Table 28-9. 2-wire Serial Bus Requirements (Continued)
Parameter
Condition
Symbol
Min
Max
Unit
1000ns
----------------
VCC – 0,4V
---------------------------
3mA
fSCL ≤ 100kHz
Rp
Ω
Cb
Value of pull-up resistor
VCC – 0,4V
---------------------------
3mA
300ns
-------------
fSCL > 100kHz
Rp
Ω
Cb
fSCL ≤ 100kHz
fSCL > 100kHz
fSCL ≤ 100kHz(6)
fSCL > 100kHz(7)
fSCL ≤ 100kHz
fSCL > 100kHz
fSCL ≤ 100kHz
fSCL > 100kHz
fSCL ≤ 100kHz
fSCL > 100kHz
fSCL ≤ 100kHz
fSCL > 100kHz
fSCL ≤ 100kHz
fSCL > 100kHz
fSCL ≤ 100kHz
fSCL > 100kHz
4.0
0.6
4.7
1.3
4.0
0.6
4.7
0.6
0
–
–
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
ns
ns
µs
µs
µs
µs
Hold time (repeated) START condition
Low period of the SCL clock
High period of the SCL clock
Set-up time for a repeated START condition
Data hold time
tHD;STA
–
tLOW
–
–
tHIGH
–
–
tSU;STA
tHD;DAT
tSU;DAT
tSU;STO
tBUF
–
3.45
0.9
–
0
250
100
4.0
0.6
4.7
1.3
Data setup time
–
–
Setup time for STOP condition
–
–
Bus free time between a STOP and START
condition
–
Notes: 1. In ATmega164P-B/324P-B/644P-B, this parameter is characterized and not 100% tested.
2. Required only for fSCL > 100kHz.
3. Cb = capacitance of one bus line in pF.
4.
fCK = CPU clock frequency
5. This requirement applies to all ATmega164P-B/324P-B/644P-B two-wire serial interface operation. Other devices con-
nected to the two-wire serial bus need only obey the general fSCL requirement.
6. The actual low period generated by the ATmega164P-B/324P-B/644P-B two-wire serial interface is (1/fSCL – 2/fCK), thus
fCK must be greater than 6MHz for the low time requirement to be strictly met at fSCL = 100kHz.
7. The actual low period generated by the ATmega164P-B/324P-B/644P-B two-wire serial interface is
(1/fSCL – 2/fCK), thus the low time requirement will not be strictly met for fSCL > 308kHz when fCK = 8MHz. Still,
ATmega164P-B/324P-B/644P-B devices connected to the bus may communicate at full speed (400kHz) with other
ATmega164P-B/324P-B/644P-B devices, as well as any other device with a proper tLOW acceptance margin.
Figure 28-5. 2-wire Serial Bus Timing
tof
tHIGH
tr
tLOW
tLOW
SCL
SDA
tHD,STA
tHD,DAT
tSU,DAT
tHD,STA
tSU,STA
tBUF
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28.9 ADC Characteristics
Table 28-10. ADC Characteristics, Single Ended Channel
Parameter
Condition
Symbol
Min
Typ.
Max
Unit
Resolution
Single ended conversion
10
Bit
VCC = 4V, VREF = 4V, ADC
clock = 200kHz
TUE
TUE
2.5
4
4
LSB
Absolute accuracy
VCC = 4V, VREF = 4V, ADC
clock = 200kHz, Noise
reduction mode on.
2.5
LSB
VCC = 4V, VREF = 4V, ADC
clock = 200kHz
Integral non linearity
Differential non linearity
Gain error
INL
0.5
0.3
–2
2
1.5
0.7
4
LSB
LSB
LSB
LSB
VCC = 4V, VREF = 4V, ADC
clock = 200kHz
DNL
VCC = 4V, VREF = 4V, ADC
clock = 200kHz
–4
4
VCC = 4V, VREF = 4V, ADC
clock = 200kHz
Offset error
4
Conversion time
Free running conversion
Single ended conversion
65
50
260
200
µs
kHz
V
Clock frequency
Analog supply voltage
Reference voltage
AVCC
VREF
VIN
VCC – 0.3
1.00
VCC + 0.3
AVCC
VREF
V
Input voltage
GND
0.96
V
Internal voltage reference
Internal voltage reference
Reference input resistance
Analog input resistance
1.1V
VINT1
VINT2
RREF
RAIN
1.1
2.56
1.2
V
2.56V, VCC > 2.7V
2.33
2.79
V
30 ±40%
100
kΩ
MΩ
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Table 28-11. ADC Characteristics, Differential Channels
Parameter
Condition
Gain = 1x
Symbol
Min
Typ.
Max
Unit
8
8
7
Resolution
Gain = 10x
Gain = 200x
Bit
Gain = 1x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
4.6
4.8
1.0
0.3
0.3
0.3
0.2
0.2
0.3
–9
7
8
Absolute accuracy (including INL,
DNL quantization error and offset
error)
Gain = 10x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
TUE
Gain = 200x
VCC = 5V, VREF = 4V
4
ADC clock = 200kHz
Gain = 1x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
1.5
1.5
1.5
1.0
1.0
1.0
–4
–4
3
Gain = 10x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
Integral non-linearity (INL)
Differential non-linearity (DNL)
Gain error
INL
LSB
Gain = 200x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
Gain = 1x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
Gain = 10x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
DNL
Gain = 200x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
Gain = 1x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
–12
–12
–3
Gain = 10x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
–9
Gain = 200x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
–1
LSB
Gain = 1x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
–4
0.3
0.2
-0.5
4
Gain = 10x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
Offset error
–4
4
Gain = 200x
VCC = 5V, VREF = 4V
ADC clock = 200kHz
–4
3
AVCC –
0.5
Reference voltage
VREF
2.56
V
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29. Typical Characteristics
The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption
measurements are performed with all I/O pins configured as inputs and with internal pull-ups enabled. A sine wave generator
with rail-to-rail output is used as clock source.
All active- and idle current consumption measurements are done with all bits in the PRR registers set and thus, the
corresponding I/O modules are turned off. Also the analog comparator is disabled during these measurements. The power
consumption in power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating frequency, loading of I/O pins,
switching rate of I/O pins, code executed and ambient temperature. The dominating factors are operating voltage and
frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL × VCC × f where CL = load capacitance,
VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to function properly at
frequencies higher than the ordering code indicates.
The difference between current consumption in power-down mode with watchdog timer enabled and power-down mode with
watchdog timer disabled represents the differential current drawn by the watchdog timer.
29.1 ATmega164P-B Typical Characteristics
29.1.1 Active Supply Current
Figure 29-1. ATmega164P-B: Active Supply Current versus Low Frequency (0.1 - 1.0MHz)
1.6
6.0
1.4
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
1.2
1.0
0.8
0.6
0.4
0.2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
Figure 29-2. ATmega164P-B: Active Supply Current versus Frequency (1 - 16MHz)
18
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
16
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
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29.1.2 Idle Supply Current
Figure 29-3. ATmega164P-B: Idle Supply Current versus Low Frequency (0.1 - 1.0MHz)
0.3
0.25
0.2
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
0.15
0.1
0.05
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
Figure 29-4. ATmega164P-B: Idle Supply Current versus Frequency (1 - 16MHz)
4
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
3.5
3
2.5
2
1.5
1
0.5
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
29.1.3 Power-down Supply Current
Figure 29-5. ATmega164P-B: Power-down Supply Current versus VCC (Watchdog Timer Disabled)
120
100
80
150
125
60
40
85
25
-40
20
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
298
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-6. ATmega164P-B: Power-down Supply Current versus VCC (Watchdog Timer Enabled)
120
100
80
150
125
60
40
85
25
-40
20
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
29.1.4 Pin Pull-up
Figure 29-7. ATmega164P-B: I/O Pin Pull-up Resistor Current versus Input Voltage (VCC = 5V)
160
140
120
100
80
150
125
85
25
-40
60
40
20
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VOP (V)
Figure 29-8. ATmega164P-B: Reset Pull-up Resistor Current versus Reset Pin Voltage (VCC =5V)
120
100
150
80
60
125
85
25
40
20
0
-40
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VRESET (V)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
299
9255E–AVR–08/14
29.1.5 Pin Driver Strength
Figure 29-9. ATmega164P-B: I/O Pin Output Voltage versus Sink Current (VCC = 3V)
1.4
1.2
1
150
125
85
0.8
0.6
25
-40
0.4
0.2
0
1
3
5
7
9
11
13
15
17
19
Load Current (mA)
Figure 29-10. ATmega164P-B: I/O Pin Output Voltage versus Sink Current (VCC = 5V)
1
0.9
0.8
150
125
85
0.7
0.6
0.5
25
0.4
0.3
0.2
-40
0.1
0
1
3
5
7
9
11
13
15
17
19
Load Current (mA)
Figure 29-11. ATmega164P-B: I/O Pin Output Voltage versus Source Current (VCC = 3V)
3.5
3
2.5
150
125
85
2
1.5
1
25
-40
0.5
0
0
2
4
6
8
10
12
14
16
18
20
Load Current (mA)
300
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-12. ATmega164P-B: I/O Pin Output Voltage versus Source Current (VCC = 5V)
5.2
5
150
125
85
4.8
4.6
4.4
25
-40
4.2
4
0
2
4
6
8
10
12
14
16
18
20
Load Current (mA)
29.1.6 Pin Threshold
Figure 29-13. ATmega164P-B: I/O Pin Input Threshold versus VCC (VIH, I/O Pin Read as ‘1’)
4
3.5
3
150
125
85
2.5
2
25
1.5
1
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-14. ATmega164P-B: I/O Pin Input Threshold versus VCC (VIL, I/O Pin Read as ‘0’)
3
2.5
150
125
85
2
1.5
1
25
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
301
9255E–AVR–08/14
Figure 29-15. ATmega164P-B: Reset Pin Input Threshold versus VCC (VIH, I/O Pin Read as ‘1’)
5
4.5
4
3.5
3
150
125
85
2.5
2
25
-40
1.5
1
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-16. ATmega164P-B: Reset Pin Input Threshold versus VCC (VIL, I/O Pin Read as ‘0’)
2.5
2
150
125
85
1.5
25
1
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
29.1.7 BOD Threshold
Figure 29-17. ATmega164P-B: BOD Threshold versus Temperature (VBOT = 4.3V)
4.6
4.5
4.4
1
0
4.3
4.2
4.1
4
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
302
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-18. ATmega164P-B: BOD Threshold versus Temperature (VBOT = 2.7V)
2.9
2.85
2.8
2.75
1
0
2.7
2.65
2.6
2.55
2.5
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
Figure 29-19. ATmega164P-B: Calibrated Bandgap Voltage versus VCC
1.2
1.18
1.16
1.14
1.12
150
125
85
1.10
1.08
25
-40
1.06
1.04
1.02
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 29-20. ATmega164P-B: Bandgap Voltage versus Temperature
1.2
1.18
1.16
5.5
1.14
1.12
1.1
5.0
4.5
3.6
3.0
1.08
2.7
1.8
1.06
1.04
1.02
1
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
303
9255E–AVR–08/14
29.1.8 Internal Oscillator Speed
Figure 29-21. ATmega164P-B: Watchdog Oscillator Frequency versus Temperature
140
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
1.8
135
130
125
120
115
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
Figure 29-22. ATmega164P-B: Watchdog Oscillator Frequency versus VCC
140
135
130
125
120
115
150
125
85
25
-40
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 29-23. ATmega164P-B: Calibrated 8MHz RC Oscillator versus VCC
8.15
8.1
8.05
150
125
85
8
7.95
7.9
25
7.85
7.8
-40
7.75
7.7
7.65
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
304
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-24. ATmega164P-B: Calibrated 8MHz RC Oscillator versus Temperature
8.15
8.1
5.5
5.0
8.05
8
7.95
7.9
4.5
4.0
3.6
7.85
3.0
2.7
7.8
1.8
7.75
7.7
7.65
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
Figure 29-25. ATmega164P-B: Calibrated 8MHz RC Oscillator versus OSCCAL Value
18
16
14
12
10
8
150
125
85
25
-40
6
4
2
0
0
16
32
48
64
80
96
112 128 144 160 176 192 208 224 240
OSCCAL (X1)
29.2 ATmega324P-B Typical Characteristics
29.2.1 Active Supply Current
Figure 29-26. ATmega324P-B: Active Supply Current versus Low Frequency (0.1 - 1.0MHz)
1.6
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
305
9255E–AVR–08/14
Figure 29-27. ATmega324P-B: Active Supply Current versus Frequency (1 - 16MHz)
18
16
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
29.2.2 Idle Supply Current
Figure 29-28. ATmega324P-B: Idle Supply Current versus Low Frequency (0.1 - 1.0MHz)
0.35
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
1.6
0.3
0.25
0.2
0.15
0.1
0.05
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
Figure 29-29. ATmega324P-B: Idle Supply Current versus Frequency (1 - 16MHz)
4
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.3
2.7
2.4
2.2
2.0
1.8
3.5
3
2.5
2
1.5
1
0.5
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
306
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
29.2.3 Power-down Supply Current
Figure 29-30. ATmega324P-B: Power-down Supply Current versus VCC (Watchdog Timer Disabled)
120
100
80
150
125
85
60
40
25
20
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-31. ATmega324P-B: Power-down Supply Current versus VCC (Watchdog Timer Enabled)
120
100
80
150
125
85
60
40
25
20
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
29.2.4 Pin Pull-up
Figure 29-32. ATmega324P-B: I/O Pin Pull-up Resistor Current versus Input Voltage (VCC = 5V)
160
140
120
150
125
100
80
85
25
-40
60
40
20
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VOP (V)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
307
9255E–AVR–08/14
Figure 29-33. ATmega324P-B: Reset Pull-up Resistor Current versus Reset Pin Voltage (VCC = 5V)
120
100
80
60
150
125
85
40
20
0
25
-40
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VRESET (V)
29.2.5 Pin Driver Strength
Figure 29-34. ATmega324P-B: I/O Pin Output Voltage versus Sink Current (VCC = 3V)
1.4
1.2
1
150
125
85
0.8
0.6
25
-40
0.4
0.2
0
1
3
5
7
9
11
13
15
17
19
Load Current (mA)
Figure 29-35. ATmega324P-B: I/O Pin Output Voltage versus Sink Current (VCC = 5V)
1.4
1.2
1
150
125
85
0.8
0.6
25
-40
0.4
0.2
0
1
3
5
7
9
11
13
15
17
19
Load Current (mA)
308
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-36. ATmega324P-B: I/O Pin Output Voltage versus Source Current (VCC = 3V)
3.5
3
2.5
150
125
85
2
1.5
1
25
-40
0.5
0
0
2
4
6
8
10
12
14
16
18
20
Load Current (mA)
Figure 29-37. ATmega324P-B: I/O Pin Output Voltage versus Source Current (VCC = 5V)
5.2
5
4.8
4.6
4.4
150
125
85
25
-40
4.2
4
0
2
4
6
8
10
12
14
16
18
20
Load Current (mA)
29.2.6 Pin Threshold
Figure 29-38. ATmega324P-B: I/O Pin Input Threshold versus VCC (VIH, I/O Pin Read as ‘1’)
4
3.5
3
150
125
85
2.5
2
25
1.5
1
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
309
9255E–AVR–08/14
Figure 29-39. ATmega324P-B: I/O Pin Input Threshold versus VCC (VIL, I/O Pin Read as ‘0’)
3
2.5
150
125
85
2
1.5
1
25
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-40. ATmega324P-B: Reset Pin Input Threshold versus VCC (VIH, I/O Pin Read as ‘1’)
5
4.5
4
3.5
3
150
125
85
2.5
2
25
-40
1.5
1
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-41. ATmega324P-B: Reset Pin Input Threshold versus VCC (VIL, I/O Pin Read as ‘0’)
2.5
2
1.5
1
150
125
85
25
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
310
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
29.2.7 BOD Threshold
Figure 29-42. ATmega324P-B: BOD Threshold versus Temperature (VBOT = 4.3V)
4.6
4.5
4.4
4.3
1
0
4.2
4.1
4
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
Figure 29-43. ATmega324P-B: BOD Threshold versus Temperature (VBOT = 2.7V)
2.9
2.85
2.8
1
2.75
2.7
0
2.65
2.6
2.55
2.5
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
Figure 29-44. ATmega324P-B: Calibrated Bandgap Voltage versus VCC
1.2
1.18
1.16
1.14
1.12
150
125
85
1.10
1.08
25
1.06
-40
1.04
1.02
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
311
9255E–AVR–08/14
Figure 29-45. ATmega324P-B: Bandgap Voltage versus Temperature
1.2
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
1.8
1.18
1.16
1.14
1.12
1.1
1.08
1.06
1.04
1.02
1
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (V)
29.2.8 Internal Oscillator Speed
Figure 29-46. ATmega324P-B: Watchdog Oscillator Frequency versus Temperature
140
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
1.8
135
130
125
120
115
110
105
100
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
Figure 29-47. ATmega324P-B: Watchdog Oscillator Frequency versus VCC
140
135
130
125
150
125
85
120
115
25
-40
110
105
100
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
312
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-48. ATmega324P-B: Calibrated 8MHz RC Oscillator versus VCC
8.6
150
125
85
8.4
8.2
8
25
-40
7.8
7.6
7.4
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 29-49. ATmega324P-B: Calibrated 8MHz RC Oscillator versus Temperature
8.6
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
1.8
8.4
8.2
8
7.8
7.6
7.4
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
Figure 29-50. ATmega324P-B: Calibrated 8MHz RC Oscillator versus OSCCAL Value
16
14
12
10
150
125
85
8
6
25
-40
4
2
0
0
16
32
48
64
80
96
112 128 144 160 176 192 208 224 240
OSCCAL (X1)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
313
9255E–AVR–08/14
29.3 ATmega644P-B Typical Characteristics
29.3.1 Active Supply Current
Figure 29-51. ATmega644P-B: Active Supply Current versus Low Frequency (0.1 - 1.0MHz)
1.6
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
Figure 29-52. ATmega644P-B: Active Supply Current versus Frequency (1 - 16MHz)
18
16
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
29.3.2 Idle Supply Current
Figure 29-53. ATmega644P-B: Idle Supply Current versus Low Frequency (0.1 - 1.0MHz)
0.35
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
0.3
0.25
0.2
0.15
0.1
0.05
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
314
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-54. ATmega644P-B: Idle Supply Current versus Frequency (1 - 16MHz)
4
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
2.4
2.2
2.0
1.8
3.5
3
2.5
2
1.5
1
0.5
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
29.3.3 Power-down Supply Current
Figure 29-55. ATmega644P-B: Power-down Supply Current versus VCC (Watchdog Timer Disabled)
120
100
80
150
125
85
60
40
25
20
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-56. ATmega644P-B: Power-down Supply Current versus VCC (Watchdog Timer Enabled)
140
120
100
150
125
85
80
60
40
25
20
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
315
9255E–AVR–08/14
29.3.4 Pin Pull-up
Figure 29-57. ATmega644P-B: I/O Pin Pull-up Resistor Current versus Input Voltage (VCC = 5V)
160
140
120
150
125
100
80
85
25
60
-40
40
20
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VOP (V)
Figure 29-58. ATmega644P-B: Reset Pull-up Resistor Current versus Reset Pin Voltage (VCC = 5V)
120
100
80
60
150
125
85
40
20
0
25
-40
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VRESET (V)
29.3.5 Pin Driver Strength
Figure 29-59. ATmega644P-B: I/O Pin Output Voltage versus Sink Current (VCC = 3V)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
150
125
85
25
-40
1
3
5
7
9
11
13
15
17
19
Load Current (mA)
316
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-60. ATmega644P-B: I/O Pin Output Voltage versus Sink Current (VCC = 5V)
1.4
1.2
1
150
125
85
0.8
0.6
25
-40
0.4
0.2
0
1
3
5
7
9
11
13
15
17
19
Load Current (mA)
Figure 29-61. ATmega644P-B: I/O Pin Output Voltage versus Source Current (VCC = 3V)
3.5
3
2.5
2
150
125
85
1.5
25
1
-40
0.5
0
0
2
4
6
8
10
12
14
16
18
20
Load Current (mA)
Figure 29-62. ATmega644P-B: I/O Pin Output Voltage versus Source Current (VCC = 5V)
5.2
5
4.8
4.6
4.4
150
125
85
25
-40
4.2
4
0
2
4
6
8
10
12
14
16
18
20
Load Current (mA)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
317
9255E–AVR–08/14
29.3.6 Pin Threshold
Figure 29-63. ATmega644P-B: I/O Pin Input Threshold versus VCC (VIH, I/O Pin Read as ‘1’)
4
3.5
3
150
125
85
2.5
2
25
1.5
1
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-64. ATmega644P-B: I/O Pin Input Threshold versus VCC (VIL, I/O Pin Read as ‘0’)
3
2.5
150
125
85
2
1.5
1
25
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-65. ATmega644P-B: Reset Pin Input Threshold versus VCC (VIH, I/O Pin Read as ‘1’)
5
4.5
4
3.5
3
150
125
85
2.5
2
25
-40
1.5
1
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
318
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-66. ATmega644P-B: Reset Pin Input Threshold versus VCC (VIL, I/O Pin Read as ‘0’)
2.5
2
1.5
1
150
125
85
25
-40
0.5
0
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
29.3.7 BOD Threshold
Figure 29-67. ATmega644P-B: BOD Threshold versus Temperature (VBOT = 4.3V)
4.6
4.5
4.4
4.3
1
0
4.2
4.1
4
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
Figure 29-68. ATmega644P-B: BOD Threshold versus Temperature (VBOT = 2.7V)
2.9
2.85
2.8
1
0
2.75
2.7
2.65
2.6
2.55
2.5
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
319
9255E–AVR–08/14
Figure 29-69. ATmega644P-B: Calibrated Bandgap Voltage versus VCC
1.2
1.18
1.16
1.14
1.12
150
125
85
1.1
1.08
25
1.06
-40
1.04
1.02
1
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-70. ATmega644P-B: Bandgap Voltage versus Temperature
1.2
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
1.8
1.18
1.16
1.14
1.12
1.1
1.08
1.06
1.04
1.02
1
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (V)
29.3.8 Internal Oscillator Speed
Figure 29-71. ATmega644P-B: Watchdog Oscillator Frequency versus Temperature
160
6.0
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
1.8
150
140
130
120
110
100
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
320
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
Figure 29-72. ATmega644P-B: Watchdog Oscillator Frequency versus VCC
160
150
140
130
120
110
150
125
85
25
-40
100
1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
VCC (V)
Figure 29-73. ATmega644P-B: Calibrated 8MHz RC Oscillator versus VCC
8.6
8.4
8.2
8
150
125
85
25
-40
7.8
7.6
7.4
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 29-74. ATmega644P-B: Calibrated 8MHz RC Oscillator versus Temperature
8.6
5.5
5.0
4.5
4.0
3.6
3.3
3.0
2.7
1.8
8.4
8.2
8
7.8
7.6
7.4
-40
-20 -10
0
10 20 30 40
60 70 80 90 100 110 120 130 140 150
-30
50
Temperature (°C)
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
321
9255E–AVR–08/14
Figure 29-75. ATmega644P-B: Calibrated 8MHz RC Oscillator versus OSCCAL Value
25
150
125
85
20
15
25
-40
10
5
0
0
16
32
48
64
80
96
112 128 144 160 176 192 208 224 240
OSCCAL (X1)
322
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
30. Register Summary
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
(0xFF)
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
(0xFE)
-
-
(0xFD) Reserved
Reserved
(0xFC)
-
-
-
-
-
-
-
-
TCCR2B
(0xFB)
(0xFA)
(0xF9)
(0xF8)
(0xF7)
Reserved
Reserved
Reserved
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Reserved
TCCR2B
(0xF6)
-
-
-
-
-
-
-
-
(0xF5)
(0xF4)
(0xF3)
Reserved
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Reserved
TCCR2B
(0xF2)
-
-
-
-
-
-
-
-
(0xF1)
(0xF0)
(0xEF)
Reserved
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
(0xEE) Reserved
(0xED) Reserved
-
-
Reserved
(0xEC)
-
-
-
-
-
-
-
-
TCCR2B
(0xEB) Reserved
(0xEA) Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
(0xE9)
Reserved
Reserved
TCCR2B
(0xE8)
-
-
-
-
-
-
-
-
(0xE7)
(0xE6)
(0xE5)
Reserved
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Reserved
TCCR2B
(0xE4)
-
-
-
-
-
-
-
-
(0xE3)
(0xE2)
(0xE1)
(0xE0)
Reserved
Reserved
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate
on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O
registers as data space using LD and ST instructions, $20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from $60 - $FF,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. USART in SPI master mode.
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
323
9255E–AVR–08/14
30. Register Summary (Continued)
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
(0xDF) Reserved
(0xDE) Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Reserved
(0xDD)
-
-
-
-
-
-
-
-
TCCR2B
(0xDC) Reserved
(0xDB) Reserved
(0xDA) Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
(0xD9)
(0xD8)
(0xD7)
(0xD6)
(0xD5)
(0xD4)
(0xD3)
(0xD2)
(0xD1)
(0xD0)
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
(0xCF) Reserved
USART1 I/O data register
USART0 I/O data register
(0xCE)
UDR1
163
(0xCD)
(0xCC)
UBRR1H
UBRR1L
-
-
-
-
-
-
-
USART1 baud rate register high byte
166/175
166/175
USART1 baud rate Register low byte
(0xCB) Reserved
-
-
-
-
-
(0xCA)
(0xC9)
(0xC8)
(0xC7)
UCSR1C UMSEL11 UMSEL10 UPM11
UPM10
RXEN1
FE1
USBS1
TXEN1
DOR1
-
UCSZ11/UDORD0(5) UCSZ10/UCPHA0(5) UCPOL1 165/175
UCSR1B RXCIE1
TXCIE1
TXC1
-
UDRIE1
UDRE1
-
UCSZ12
UPE1
-
RXB81
U2X1
-
TXB81 164/174
UCSR1A
Reserved
RXC1
-
MPCM1 163/173
-
-
USART0 I/O data register
USART0 I/O data register
(0xC6)
UDR0
163
(0xC5)
(0xC4)
(0xC3)
(0xC2)
(0xC1)
(0xC0)
(0xBF)
UBRR0H
UBRR0L
Reserved
-
-
-
-
-
-
-
USART0 baud rate register high byte
166/175
USART0 baud rate register low byte
166/175
-
-
-
USBS0
TXEN0
DOR0
-
-
-
UCSR0C UMSEL01 UMSEL00 UPM01
UPM00
UCSZ01/UDORD0(5) UCSZ00/UCPHA0(5) UCPOL0 165/175
UCSR0B RXCIE0
TXCIE0
UDRIE0
RXEN0
UCSZ02
RXB80
TXB80 164/174
UCSR0A
Reserved
RXC0
TXC0
UDRE0
FE0
UPE0
U2X0
MPCM0 163/173
-
-
-
-
-
-
-
-
-
-
-
-
-
-
(0xBE) Reserved
-
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate
on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O
registers as data space using LD and ST instructions, $20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from $60 - $FF,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. USART in SPI master mode.
324
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
30. Register Summary (Continued)
Address
(0xBD)
(0xBC)
(0xBB)
(0xBA)
(0xB9)
(0xB8)
(0xB7)
(0xB6)
(0xB5)
(0xB4)
(0xB3)
(0xB2)
(0xB1)
(0xB0)
(0xAF)
Name
TWAMR
TWCR
Bit 7
Bit 6
TWAM5
TWEA
Bit 5
Bit 4
Bit 3
Bit 2
TWAM1
TWEN
Bit 1
TWAM0
-
Bit 0
-
Page
203
200
202
203
202
200
TWAM6
TWINT
TWAM4
TWSTA
TWAM3
TWSTO
TWAM2
TWWC
TWIE
TWDR
2-wire serial interface data register
TWAR
TWA6
TWS7
TWA5
TWS6
TWA4
TWS5
TWA3
TWS4
TWA2
TWS3
TWA1
-
TWA0
TWGCE
TWPS0
TWSR
TWPS1
TWBR
2-wire serial interface bit rate register
Reserved
ASSR
-
-
-
-
-
AS2
-
-
-
-
-
-
EXCLK
-
TCN2UB
-
OCR2AB
-
OCR2BUB
-
TCR2AUB
-
TCR2BB
-
136
Reserved
OCR2B
OCR2A
TCNT2
TCCR2B
Timer/Counter2 output compare register B
Timer/Counter2 output compare register A
Timer/Counter2 (8 bit)
136
136
136
135
132
FOC2A
FOC2B
-
-
WGM22
CS22
CS21
CS20
TCCR2A COM2A1 COM2A0 COM2B1 COM2B0
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
WGM21
WGM20
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
(0xAE) Reserved
(0xAD) Reserved
(0xAC) Reserved
(0xAB) Reserved
(0xAA) Reserved
(0xA9)
(0xA8)
(0xA7)
(0xA6)
(0xA5)
(0xA4)
(0xA3)
(0xA2)
(0xA1)
(0xA0)
(0x9F)
(0x9E)
(0x9D)
(0x9C)
(0x9B)
(0x9A)
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
OCR3BH
OCR3BL
Timer/Counter3 - output compare register B high byte
Timer/Counter3 - output compare register B low byte
114
114
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate
on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O
registers as data space using LD and ST instructions, $20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from $60 - $FF,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. USART in SPI master mode.
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
325
9255E–AVR–08/14
30. Register Summary (Continued)
Address
(0x99)
(0x98)
(0x97)
(0x96)
(0x95)
(0x94)
(0x93)
(0x92)
(0x91)
(0x90)
(0x8F)
(0x8E)
(0x8D)
(0x8C)
(0x8B)
(0x8A)
(0x89)
(0x88)
(0x87)
(0x86)
(0x85)
(0x84)
(0x83)
(0x82)
(0x81)
(0x80)
(0x7F)
(0x7E)
(0x7D)
(0x7C)
(0x7B)
(0x7A)
(0x79)
(0x78)
(0x77)
(0x76)
Name
OCR3AH
OCR3AL
ICR3H
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
113
113
114
114
113
113
Timer/Counter3 - output compare register A high byte
Timer/Counter3 - output compare register A low byte
Timer/Counter3 - input capture register high byte
Timer/Counter3 - input capture register low byte
Timer/Counter3 - counter register high byte
ICR3L
TCNT3H
TCNT3L
Reserved
TCCR3C
TCCR3B
Timer/Counter3 - counter register low byte
-
-
-
-
-
-
-
-
-
-
FOC3A
ICNC3
FOC3B
ICES3
-
-
-
-
-
112
111
109
WGM33
WGM32
CS32
CS31
CS30
TCCR3A COM3A1 COM3A0 COM3B1 COM3B0
-
-
-
-
-
-
-
-
-
-
WGM31
WGM30
Reserved
Reserved
Reserved
Reserved
OCR1BH
OCR1BL
OCR1AH
OCR1AL
ICR1H
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Timer/Counter1 - output compare register B high byte
Timer/Counter1 - output compare register B low byte
Timer/Counter1 - output compare register A high byte
Timer/Counter1 - output compare register A low byte
Timer/Counter1 - input capture register high byte
Timer/Counter1 - input capture register low byte
Timer/Counter1 - counter register high byte
114
114
113
113
114
114
113
113
ICR1L
TCNT1H
TCNT1L
Reserved
TCCR1C
TCCR1B
Timer/Counter1 - counter register low byte
-
-
-
-
-
-
-
-
-
-
FOC1A
ICNC1
FOC1B
ICES1
-
-
-
CS12
-
-
-
112
111
109
206
224
WGM13
WGM12
CS11
WGM11
AIN1D
ADC1D
-
CS10
WGM10
AIN0D
ADC0D
-
TCCR1A COM1A1 COM1A0 COM1B1 COM1B0
-
DIDR1
DIDR0
-
ADC7D
-
-
-
-
ADC4D
-
-
ADC3D
-
-
ADC6D
-
ADC5D
-
ADC2D
-
Reserved
ADMUX
ADCSRB
ADCSRA
ADCH
REFS1
-
REFS0
ACME
ADSC
ADLAR
-
MUX4
-
MUX3
-
MUX2
ADTS2
ADPS2
MUX1
ADTS1
ADPS1
MUX0
ADTS0
ADPS0
220
205
222
223
223
ADEN
ADATE
ADIF
ADIE
ADC data register high byte
ADC data register low byte
ADCL
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate
on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O
registers as data space using LD and ST instructions, $20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from $60 - $FF,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. USART in SPI master mode.
326
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
30. Register Summary (Continued)
Address
(0x75)
(0x74)
(0x73)
(0x72)
(0x71)
(0x70)
(0x6F)
(0x6E)
(0x6D)
(0x6C)
(0x6B)
(0x6A)
(0x69)
(0x68)
(0x67)
(0x66)
(0x65)
(0x64)
(0x63)
(0x62)
(0x61)
(0x60)
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
-
Bit 1
-
Bit 0
-
Page
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
PCMSK3 PCINT31 PCINT30 PCINT29 PCINT28 PCINT27
PCINT26
-
PCINT25
-
PCINT24
-
55
Reserved
TIMSK3
TIMSK2
TIMSK1
TIMSK0
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
ICIE3
OCIE3B
OCIE2B
OCIE1B
OCIE0B
PCINT18
PCINT10
PCINT2
-
OCIE3A
OCIE2A
OCIE1A
OCIE0A
PCINT17
PCINT9
PCINT1
-
TOIE3
TOIE2
TOIE1
TOIE0
PCINT16
PCINT8
PCINT0
-
116
137
115
89
-
ICIE1
-
PCMSK2 PCINT23 PCINT22 PCINT21 PCINT20 PCINT19
56
PCMSK1 PCINT15 PCINT14 PCINT13 PCINT12
PCINT11
PCINT3
-
56
PCMSK0 PCINT7
PCINT6
PCINT5
PCINT4
56
Reserved
EICRA
-
-
-
-
-
-
-
-
-
-
ISC21
ISC20
ISC11
PCIE3
-
ISC10
PCIE2
-
ISC01
PCIE1
-
ISC00
PCIE0
-
53
54
PCICR
-
-
-
-
Reserved
OSCCAL
Reserved
PRR
Oscillator calibration register
32
39
-
-
-
-
-
-
PRSPI
-
-
-
PRADC
-
PRTWI
PRTIM2 PRTIM0 PRUSART1 PRTIM1
PRUSART0
Reserved
Reserved
CLKPR
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
CLKPCE
WDIF
-
CLKPS3
WDE
CLKPS2
WDP2
CLKPS1
WDP1
CLKPS0
WDP0
32
47
WDTCSR
WDIE
WDP3
WDCE
0x3F
(0x5F)
SREG
SPH
I
T
H
S
V
N
Z
C
10
10
10
0x3E
(0x5E)
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
0x3D
(0x5D)
SPL
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
0x3C
(0x5C)
Reserved
Reserved
Reserved
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0x3B
(0x5B)
0x3A
(0x5A)
0x39
(0x59)
0x38
(0x58)
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate
on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O
registers as data space using LD and ST instructions, $20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from $60 - $FF,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. USART in SPI master mode.
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
327
9255E–AVR–08/14
30. Register Summary (Continued)
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
0x37
(0x57)
SPMCSR
SPMIE
RWWSB
SIGRD
RWWSRE BLBSET
PGWRT
PGERS
SPMEN
253
0x36
(0x56)
Reserved
MCUCR
MCUSR
SMCR
-
-
-
-
-
-
-
-
IVCE
PORF
SE
0x35
(0x55)
JTD
BODS
BODSE
PUD
-
WDRF
SM2
-
-
BORF
SM1
-
IVSEL
EXTRF
SM0
-
72/239
47/239
38
0x34
(0x54)
-
-
-
-
-
-
-
-
-
JTRF
0x33
(0x53)
-
-
0x32
(0x52)
Reserved
OCDR
-
0x31
(0x51)
On-chip debug register
230
222
0x30
(0x50)
ACSR
ACD
-
ACBG
-
ACO
-
ACI
-
ACIE
ACIC
ACIS1
-
ACIS0
-
0x2F
(0x4F)
Reserved
SPDR
-
-
0x2E
(0x4E)
SPI 0 data register
146
145
144
22
0x2D
(0x4D)
SPSR
SPIF0
SPIE0
WCOL0
SPE0
-
-
-
-
-
SPI2X0
SPR00
0x2C
(0x4C)
SPCR
DORD0
MSTR0
CPOL0
CPHA0
SPR01
0x2B
(0x4B)
GPIOR2
GPIOR1
Reserved
OCR0B
OCR0A
TCNT0
TCCR0B
General purpose I/O register 2
General purpose I/O register 1
0x2A
(0x4A)
22
0x29
(0x49)
-
-
-
-
-
-
-
-
0x28
(0x48)
Timer/Counter0 output compare register B
Timer/Counter0 output compare register A
Timer/Counter0 (8 bit)
88
88
88
87
88
0x27
(0x47)
0x26
(0x46)
0x25
(0x45)
FOC0A
FOC0B
-
-
WGM02
-
CS02
-
CS01
CS00
0x24
(0x44)
TCCR0A COM0A1 COM0A0 COM0B1 COM0B0
WGM01
WGM00
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate
on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O
registers as data space using LD and ST instructions, $20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from $60 - $FF,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. USART in SPI master mode.
328
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
30. Register Summary (Continued)
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
0x23
(0x43)
PSRSYN
C
GTCCR
TSM
-
-
-
-
-
PSRASY
138
0x22
(0x42)
EEARH
EEARL
EEDR
-
-
-
-
EEPROM address register high byte
19
19
19
19
22
54
54
55
0x21
(0x41)
EEPROM address register low byte
EEPROM data register
0x20
(0x40)
0x1F
(0x3F)
EECR
-
-
EEPM1
EEPM0
EERIE
EEMPE
EEPE
EERE
0x1E
(0x3E)
GPIOR0
EIMSK
General purpose I/O register 0
0x1D
(0x3D)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
INT2
INT1
INT0
0x1C
(0x3C)
EIFR
-
-
INTF2
INTF1
INTF0
0x1B
(0x3B)
PCIFR
-
PCIF3
PCIF2
PCIF1
PCIF0
0x1A
(0x3A)
Reserved
Reserved
TIFR3
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0x19
(0x39)
-
-
-
-
0x18
(0x38)
ICF3
OCF3B
OCF3A
TOV3
118
138
117
89
0x17
(0x37)
TIFR2
-
OCF2B
OCF2A
TOV2
0x16
(0x36)
TIFR1
ICF1
OCF1B
OCF1A
TOV1
0x15
(0x35)
TIFR0
-
-
-
-
-
-
OCF0B
OCF0A
TOV0
0x14
(0x34)
Reserved
Reserved
Reserved
Reserved
Reserved
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0x13
(0x33)
0x12
(0x32)
0x11
(0x31)
0x10
(0x30)
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate
on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O
registers as data space using LD and ST instructions, $20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from $60 - $FF,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. USART in SPI master mode.
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
329
9255E–AVR–08/14
30. Register Summary (Continued)
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
0x0F
(0x2F)
Reserved
-
-
-
-
-
-
-
-
0x0E
(0x2E)
Reserved
Reserved
Reserved
PORTD
DDRD
PIND
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0x0D
(0x2D)
-
-
-
-
0x0C
(0x2C)
-
-
-
-
0x0B
(0x2B)
PORTD7 PORTD6 PORTD5 PORTD4
PORTD3
DDD3
PIND3
PORTC3
DDC3
PINC3
PORTB3
DDB3
PINB3
PORTA3
DDA3
PINA3
PORTD2
DDD2
PIND2
PORTC2
DDC2
PINC2
PORTB2
DDB2
PINB2
PORTA2
DDA2
PINA2
PORTD1
DDD1
PIND1
PORTC1
DDC1
PINC1
PORTB1
DDB1
PINB1
PORTA1
DDA1
PINA1
PORTD0
DDD0
PIND0
PORTC0
DDC0
PINC0
PORTB0
DDB0
PINB0
PORTA0
DDA0
PINA0
74
74
74
73
74
74
73
73
73
73
73
73
0x0A
(0x2A)
DDD7
PIND7
DDD6
PIND6
DDD5
PIND5
DDD4
PIND4
0x09
(0x29)
0x08
(0x28)
PORTC
DDRC
PINC
PORTC7 PORTC6 PORTC5 PORTC4
0x07
(0x27)
DDC7
PINC7
DDC6
PINC6
DDC5
PINC5
DDC4
PINC4
0x06
(0x26)
0x05
(0x25)
PORTB
DDRB
PORTB7 PORTB6 PORTB5 PORTB4
0x04
(0x24)
DDB7
PINB7
DDB6
PINB6
DDB5
PINB5
DDB4
PINB4
PORTA4
DDA4
0x03
(0x23)
PINB
0x02
(0x22)
PORTA
DDRA
PORTA7 PORTA6 PORTA5
0x01
(0x21)
DDA7
PINA7
DDA6
PINA6
DDA5
PINA5
0x00
(0x20)
PINA
PINA4
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate
on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O
registers as data space using LD and ST instructions, $20 must be added to these addresses.
The ATmega164P-B/324P-B/644P-B is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from $60 - $FF,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. USART in SPI master mode.
330
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
9255E–AVR–08/14
31. Instruction Set Summary
Mnemonics Operands Description
Arithmetic and Logic Instructions
Operation
Flags #Clocks
ADD
ADC
Rd, Rr
Rd, Rr
Rdl,K
Rd, Rr
Rd, K
Rd, Rr
Rd, K
Rdl,K
Rd, Rr
Rd, K
Rd, Rr
Rd, K
Rd, Rr
Rd
Add two registers
Rd ← Rd + Rr
Z,C,N,V,H
Z,C,N,V,H
Z,C,N,V,S
Z,C,N,V,H
Z,C,N,V,H
Z,C,N,V,H
Z,C,N,V,H
Z,C,N,V,S
Z,N,V
1
1
2
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
Add with carry two registers
Add immediate to word
Subtract two registers
Subtract constant from register
Subtract with carry two registers
Subtract with carry constant from reg.
Subtract immediate from word
Logical AND registers
Logical AND register and constant
Logical OR registers
Rd ← Rd + Rr + C
Rdh: Rdl ← Rdh: Rdl + K
Rd ← Rd – Rr
ADIW
SUB
SUBI
SBC
Rd ← Rd – K
Rd ← Rd – Rr – C
Rd ← Rd – K – C
Rdh: Rdl ← Rdh: Rdl – K
Rd ← Rd × Rr
SBCI
SBIW
AND
ANDI
OR
Rd ← Rd × K
Z,N,V
Rd ← Rd v Rr
Z,N,V
ORI
Logical OR register and constant
Exclusive OR registers
One’s complement
Rd ← Rd v K
Z,N,V
EOR
COM
NEG
SBR
Rd ← Rd Rr
Z,N,V
Rd ← 0xFF − Rd
Rd ← 0x00 − Rd
Rd ← Rd v K
Z,C,N,V
Z,C,N,V,H
Z,N,V
Rd
Two’s complement
Rd,K
Rd,K
Rd
Set bit(s) in register
CBR
Clear bit(s) in register
Increment
Rd ← Rd × (0xFF – K)
Rd ← Rd + 1
Z,N,V
INC
Z,N,V
DEC
Rd
Decrement
Rd ← Rd – 1
Z,N,V
TST
Rd
Test for zero or minus
Clear register
Rd ← Rd × Rd
Z,N,V
CLR
Rd
Rd ← Rd Rd
Rd ← 0xFF
Z,N,V
SER
Rd
Set register
None
MUL
Rd, Rr
Rd, Rr
Rd, Rr
Rd, Rr
Rd, Rr
Rd, Rr
Multiply unsigned
R1:R0 ← Rd x Rr
R1:R0 ← Rd x Rr
R1:R0 ← Rd x Rr
R1:R0 ← (Rd x Rr) << 1
R1:R0 ← (Rd x Rr) << 1
Z,C
MULS
MULSU
FMUL
FMULS
FMULSU
Multiply signed
Z,C
Multiply signed with unsigned
Fractional multiply unsigned
Fractional multiply signed
Z,C
Z,C
Z,C
Fractional multiply signed with unsigned R1:R0 ← (Rd x Rr) << 1
Z,C
Branch Instructions
RJMP
k
Relative jump
PC ← PC + k + 1
PC ← Z
None
None
2
2
IJMP
Indirect jump to (Z)
Direct jump
JMP
k
k
PC ← k
None
3
RCALL
ICALL
Relative subroutine call
Indirect call to (Z)
Direct subroutine call
Subroutine return
Interrupt return
PC ← PC + k + 1
PC ← Z
None
4
None
4
CALL
k
PC ← k
None
5
RET
PC ← STACK
PC ← STACK
if (Rd = Rr) PC ← PC + 2 or 3
Rd − Rr
None
5
RETI
I
5
CPSE
CP
Rd, Rr
Rd, Rr
Rd, Rr
Rd, K
Compare, skip if equal
Compare
None
1/2/3
1
Z,N,V,C,H
Z,N,V,C,H
Z,N,V,C,H
CPC
CPI
Compare with carry
Compare register with immediate
Rd − Rr − C
Rd − K
1
1
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31. Instruction Set Summary (Continued)
Mnemonics Operands Description
Operation
Flags #Clocks
SBRC
SBRS
SBIC
Rr, b
Skip if bit in register cleared
Skip if bit in register is set
Skip if bit in I/O register cleared
Skip if bit in I/O register is set
Branch if status flag set
Branch if status flag cleared
Branch if equal
if (Rr(b)=0) PC ← PC + 2 or 3
if (Rr(b)=1) PC ← PC + 2 or 3
if (P(b)=0) PC ← PC + 2 or 3
if (P(b)=1) PC ← PC + 2 or 3
if (SREG (s) = 1) then PC ← PC + k + 1
if (SREG (s) = 0) then PC ← PC + k + 1
if (Z = 1) then PC ← PC + k + 1
if (Z = 0) then PC ← PC + k + 1
if (C = 1) then PC ← PC + k + 1
if (C = 0) then PC ← PC + k + 1
if (C = 0) then PC ← PC + k + 1
if (C = 1) then PC ← PC + k + 1
if (N = 1) then PC ← PC + k + 1
if (N = 0) then PC ← PC + k + 1
if (N V= 0) then PC ← PC + k + 1
if (N V= 1) then PC ← PC + k + 1
if (H = 1) then PC ← PC + k + 1
if (H = 0) then PC ← PC + k + 1
if (T = 1) then PC ← PC + k + 1
if (T = 0) then PC ← PC + k + 1
if (V = 1) then PC ← PC + k + 1
if (V = 0) then PC ← PC + k + 1
if (I = 1) then PC ← PC + k + 1
if (I = 0) then PC ← PC + k + 1
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
1/2/3
1/2/3
1/2/3
1/2/3
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
Rr, b
P, b
P, b
s, k
s, k
k
SBIS
BRBS
BRBC
BREQ
BRNE
BRCS
BRCC
BRSH
BRLO
BRMI
BRPL
BRGE
BRLT
BRHS
BRHC
BRTS
BRTC
BRVS
BRVC
BRIE
k
Branch if not equal
k
Branch if carry set
k
Branch if carry cleared
Branch if same or higher
Branch if lower
k
k
k
Branch if minus
k
Branch if plus
k
Branch if greater or equal, signed
Branch if less than zero, signed
Branch if half carry flag set
Branch if half carry flag cleared
Branch if T flag set
k
k
k
k
k
Branch if T flag cleared
Branch if overflow flag is set
Branch if overflow flag is cleared
Branch if interrupt enabled
Branch if interrupt disabled
k
k
k
BRID
k
Bit and Bit-test Instructions
SBI
CBI
P, b
P, b
Rd
Rd
Rd
Rd
Rd
Rd
s
Set bit in I/O register
Clear bit in I/O register
Logical shift left
I/O (P, b) ← 1
None
None
Z,C,N,V
Z,C,N,V
Z,C,N,V
Z,C,N,V
Z,C,N,V
None
SREG (s)
SREG (s)
T
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I/O (P, b) ← 0
LSL
Rd(n+1) ← Rd (n), Rd(0) ← 0
LSR
ROL
ROR
ASR
SWAP
BSET
BCLR
BST
BLD
SEC
CLC
SEN
CLN
SEZ
Logical shift right
Rotate left through carry
Rotate right through carry
Arithmetic shift right
Swap nibbles
Rd (n) ← Rd(n+1), Rd(7) ← 0
Rd(0) ← C,Rd(n+1)← Rd (n), C←Rd(7)
Rd(7) ← C, Rd (n)← Rd(n+1),C←Rd(0)
Rd (n) ← Rd(n+1), n=0..6
Rd(3..0) ← Rd(7..4),Rd(7..4)←Rd(3..0)
Flag set
SREG (s) ← 1
SREG (s) ← 0
T ← Rr (b)
Rd (b) ← T
C ← 1
s
Flag clear
Rr, b
Rd, b
Bit store from register to T
Bit load from T to register
Set carry
None
C
Clear carry
C ← 0
C
Set negative flag
Clear negative flag
Set zero flag
N ← 1
N
N ← 0
N
Z ← 1
Z
332
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
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31. Instruction Set Summary (Continued)
Mnemonics Operands Description
Operation
Z ← 0
I ← 1
Flags #Clocks
CLZ
Clear zero flag
Z
I
1
1
1
1
1
1
1
1
1
1
1
SEI
Global interrupt enable
Global interrupt disable
Set signed test flag
CLI
I ← 0
I
SES
S ← 1
S ← 0
V ← 1
V ← 0
T ← 1
T ← 0
H ← 1
H ← 0
S
S
V
V
T
T
H
H
CLS
Clear signed test flag
Set twos complement overflow.
Clear twos complement overflow
Set T in SREG
SEV
CLV
SET
CLT
Clear T in SREG
SEH
Set half carry flag in SREG
Clear half carry flag in SREG
CLH
Data Transfer Instructions
MOV
MOVW
LDI
LD
Rd, Rr
Rd, Rr
Rd, K
Move between registers
Copy register word
Rd ← Rr
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
Rd+1:Rd ← Rr+1:Rr
Rd ← K
Load immediate
Rd, X
Load indirect
Rd ← (X)
LD
Rd, X+
Rd, - X
Rd, Y
Load indirect and post-inc.
Load indirect and pre-dec.
Load indirect
Rd ← (X), X ← X + 1
X ← X – 1, Rd ← (X)
Rd ← (Y)
LD
LD
LD
Rd, Y+
Rd, -Y
Load indirect and post-inc.
Load indirect and pre-dec.
Rd ← (Y), Y ← Y + 1
Y ← Y – 1, Rd ← (Y)
Rd ← (Y + q)
LD
LDD
LD
Rd, Y+q Load indirect with displacement
Rd, Z
Rd, Z+
Rd, -Z
Load indirect
Rd ← (Z)
LD
Load indirect and post-inc.
Load indirect and pre-dec.
Rd ← (Z), Z ← Z+1
Z ← Z - 1, Rd ← (Z)
Rd ← (Z + q)
LD
LDD
LDS
ST
Rd, Z+q Load indirect with displacement
Rd, k
X, Rr
Load direct from SRAM
Store indirect
Rd ← (k)
(X) ← Rr
ST
X+, Rr
-X, Rr
Y, Rr
Store indirect and post-inc.
Store indirect and pre-dec.
Store indirect
(X) ← Rr, X ← X + 1
X ← X – 1, (X) ← Rr
(Y) ← Rr
ST
ST
ST
Y+, Rr
-Y, Rr
Y+q, Rr
Z, Rr
Store indirect and post-inc.
Store indirect and pre-dec.
Store indirect with displacement
Store indirect
(Y) ← Rr, Y ← Y + 1
Y ← Y – 1, (Y) ← Rr
(Y + q) ← Rr
ST
STD
ST
(Z) ← Rr
ST
Z+, Rr
-Z, Rr
Z+q, Rr
k, Rr
Store indirect and post-inc.
Store indirect and pre-dec.
Store indirect with displacement
Store direct to SRAM
(Z) ← Rr, Z ← Z + 1
Z ← Z – 1, (Z) ← Rr
(Z + q) ← Rr
ST
STD
STS
LPM
LPM
LPM
(k) ← Rr
Load program memory
Load program memory
Load program memory and post-inc
R0 ← (Z)
Rd, Z
Rd ← (Z)
Rd, Z+
Rd ← (Z), Z ← Z+1
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
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31. Instruction Set Summary (Continued)
Mnemonics Operands Description
Operation
(Z) ← R1:R0
Rd ← P
Flags #Clocks
SPM
IN
Store program memory
In port
None
None
None
None
None
-
Rd, P
P, Rr
Rr
1
1
2
2
OUT
PUSH
POP
Out port
P ← Rr
Push register on stack
Pop register from stack
STACK ← Rr
Rd ← STACK
Rd
MCU Control Instructions
NOP
SLEEP
WDR
No operation
Sleep
None
None
None
None
1
1
(see specific descr. for sleep function)
(see specific descr. for WDR/timer)
For on-chip debug only
Watchdog reset
Break
1
BREAK
N/A
334
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32. Ordering Information
Speed (MHz)(3)
Power Supply
Ordering Code(2)
Package(1)
Operational Range
ATmega164P-B15AZ
ATmega164P-B15MZ
ATmega324P-B15AZ
ATmega324P-B15MZ
ATmega644P-B15AZ
ATmega644P-B15MZ
ML
PW
ML
PW
ML
PW
Automotive
16
2.7 – 5.5V
(–40oC to 125oC)
Notes: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering infor-
mation and minimum quantities.
2. Pb-free packaging, complies to the European directive for restriction of hazardous substances (RoHS directive). Also
halide free and fully green.
3. For speed versus VCC see Section 28.3 “Speed Grades” on page 289.
33. Packaging Information
Table 33-1. Package Types
Package Type
ML
44-lead, Thin (1.0mm) plastic gull wing quad flat package (TQFP)
PW
44-pad, 7 x 7 x 1.0mm body, lead pitch 0.50mm, quad flat no-lead/micro lead frame package (QFN/MLF)
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9255E–AVR–08/14
Figure 33-1. ML
Drawings not scaled
A
A2
A1
D1
44
E1
e
L
0°~7°
Top View
C
Side View
D
COMMON DIMENSIONS
(Unit of Measure = mm)
Symbol MIN
NOM
MAX NOTE
A
A1
A2
D/E
D1/E1
C
1.20
0.15
1.05
12.25
10.10
0.20
0.75
0.45
0.05
0.95
11.75
9.90
0.09
0.45
0.30
E
1.00
12.00
10.00
2
b
L
b
e
n
0.80 TYP.
44
Bottom View
Notes: 1. This drawing is for general information only. Refer to JEDEC Drawing MS-026, Variation ACB.
2. Dimensions D1 and E1 do not include mold protrusion. Allowable protrusion is 0.25mm per side.
Dimensions D1 and E1 are maximum plastic body size dimensions including mold mismatch.
3. Lead coplanarity is 0.10mm maximum.
02/28/12
REV.
TITLE
DRAWING NO.
ML
GPC
AIX
ML, 44 Lds - 0.80mm Pitch, 10x10x1.00mm Body size
Thin Profile Plastic Quad Flat Package (TQFP)
Package Drawing Contact:
packagedrawings@atmel.com
I
336
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Figure 33-2. PW
Drawings not scaled
0.08
D
Seating Plane
Marked PIN# 1D
E
A3
A1
Top View
A
Side View
L
K
D2
COMMON DIMENSIONS
(Unit of Measure = mm)
Pin 1#
Triangle
Option A
Option B
Option C
Symbol MIN
NOM
MAX NOTE
A
A1
A3
D/E
D2/E2
L
0.80
1.00
0.02
0.20 REF
7.00
0.05
Pin 1#
Chamfer
(C 0.30)
E2
3
6.90
5.00
0.45
7.10
5.40
0.65
5.20
2
0.55
1
Pin 1#
Notch
K
0.35
(C 0.20 R)
b
0.18
0.23
0.30
2
b
e
K
e
n
0.50 BSC
44
PIN# 1 Corner
Bottom View
Notes: 1. This drawing is for general information only. Refer to JEDEC Drawing MO-220, Variation VKKD-1, for proper dimensions, tolerances, datums, etc.
2. Dimensions b applies to metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip.
If the terminal has the optical radius on the other end of the terminal, the dimensions should not be measured in that radius area.
02/17/12
REV.
TITLE
DRAWING NO.
PW
GPC
ZCP
PW, 44 Leads - 0.50mm Pitch, 7x7x1mm Body size
Very Thin Quad Flat Package (Punched) (VQFN) Sawn
Package Drawing Contact:
packagedrawings@atmel.com
H
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34. Errata
34.1 Errata for ATmega164P-B
34.1.1 Rev. E
No known errata.
34.2 Errata for ATmega324P-B
34.2.1 Rev. F
No known errata.
34.3 Errata for ATmega644P-B
34.3.1 Rev. G
No known errata.
35. Revision History
Please note that the following page numbers referred to in this section refer to the specific revision mentioned, not to this
document.
Revision No.
History
9255E-AVR-08/14
• Put datasheet in the latest template
338
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36. Table of Contents
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.
Pin Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1
Pinout - TQFP/QFN/MLF for ATmega164P-B/324P-B/644P-B . . . . . . . . . . . . . . . . . . . . . . . . 3
2.
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Automotive Quality Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Comparison Between ATmega164P-B, ATmega324P-B and ATmega644P-B. . . . . . . . . . . . 5
Pin Descriptions 6
2.2
2.3
2.4
3.
4.
5.
6.
7.
Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
About Code Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Data Retention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Capacitive Touch Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
AVR CPU Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
ALU – Arithmetic Logic Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
General Purpose Register File. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Stack Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Instruction Execution Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Reset and Interrupt Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.2
7.3
7.4
7.5
7.6
7.7
8.
9.
AVR Memories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
In-System Reprogrammable Flash Program Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
SRAM Data Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
EEPROM Data Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
I/O Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.2
8.3
8.4
8.5
8.6
System Clock and Clock Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1
Clock Systems and their Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Low Power Crystal Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Full Swing Crystal Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Low Frequency Crystal Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Calibrated Internal RC Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
128kHz Internal Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
External Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Timer/Counter Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.2
9.3
9.4
9.5
9.6
9.7
9.8
9.9
9.10 Clock Output Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.11 System Clock Prescaler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.12 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
10. Power Management and Sleep Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10.2 Sleep Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10.3 BOD Disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
10.4 Idle Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
10.5 ADC Noise Reduction Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
ATmega164P-B/ATmega324P-B/ATmega644P-B [DATASHEET]
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10.6 Power-down Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
10.7 Power-save Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.8 Standby Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.9 Extended Standby Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.10 Power Reduction Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.11 Minimizing Power Consumption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.12 Register Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
11. System Control and Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
11.1 Resetting the AVR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
11.2 Internal Voltage Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
11.3 Watchdog Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
11.4 Register Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
12. Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
12.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
12.2 Interrupt Vectors in ATmega164P-B/324P-B/644P-B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
12.3 Register Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
13. External Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
13.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
13.2 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
14. I/O-Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
14.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
14.2 Ports as General Digital I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
14.3 Alternate Port Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
14.4 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
15. 8-bit Timer/Counter0 with PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
15.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
15.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
15.3 Timer/Counter Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
15.4 Counter Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
15.5 Output Compare Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
15.6 Compare Match Output Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
15.7 Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
15.8 Timer/Counter Timing Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
15.9 Register Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
16. 16-bit Timer/Counter1 and Timer/Counter3 with PWM . . . . . . . . . . . . . . . . . . . . . . . . . 90
16.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
16.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
16.3 Accessing 16-bit Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
16.4 Timer/Counter Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
16.5 Counter Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
16.6 Input Capture Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
16.7 Output Compare Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
16.8 Compare Match Output Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
16.9 Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
16.10 Timer/Counter Timing Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
16.11 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
17. 8-bit Timer/Counter2 with PWM and Asynchronous Operation . . . . . . . . . . . . . . . . . 119
17.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
17.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
17.3 Timer/Counter Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
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17.4 Counter Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
17.5 Output Compare Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
17.6 Compare Match Output Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
17.7 Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
17.8 Timer/Counter Timing Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
17.9 Asynchronous Operation of Timer/Counter2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
17.10 Timer/Counter Prescaler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
17.11 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
18. SPI – Serial Peripheral Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
18.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
18.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
18.3 SS Pin Functionality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
18.4 Data Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
18.5 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
19. USART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
19.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
19.2 USART1 and USART0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
19.3 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
19.4 Clock Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
19.5 Frame Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
19.6 USART Initialization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
19.7 Data Transmission – The USART Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
19.8 Data Reception – The USART Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
19.9 Asynchronous Data Reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
19.10 Multi-processor Communication Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
19.11 Register Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
19.12 Examples of Baud Rate Setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
20. USART in SPI Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
20.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
20.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
20.3 Clock Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
20.4 SPI Data Modes and Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
20.5 Frame Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
20.6 Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
20.7 AVR USART MSPIM versus AVR SPI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
20.8 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
21. Two-wire Serial Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
21.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
21.2 Two-wire Serial Interface Bus Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
21.3 Data Transfer and Frame Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
21.4 Multi-master Bus Systems, Arbitration and Synchronization . . . . . . . . . . . . . . . . . . . . . . . . 179
21.5 Overview of the TWI Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
21.6 Using the TWI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
21.7 Transmission Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
21.8 Multi-master Systems and Arbitration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
21.9 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
22. AC - Analog Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
22.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
22.2 Analog Comparator Multiplexed Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
22.3 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
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23. ADC - Analog-to-digital Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
23.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
23.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
23.3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
23.4 Starting a Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
23.5 Prescaling and Conversion Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
23.6 Changing Channel or Reference Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
23.7 ADC Noise Canceler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
23.8 ADC Conversion Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
23.9 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
24. JTAG Interface and On-chip Debug System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
24.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
24.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
24.3 TAP – Test Access Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
24.4 TAP Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
24.5 Using the Boundary-scan Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
24.6 Using the On-chip Debug System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
24.7 On-chip Debug Specific JTAG Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
24.8 Using the JTAG Programming Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
24.9 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
24.10 Register Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
25. IEEE 1149.1 (JTAG) Boundary-scan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
25.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
25.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
25.3 Data Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
25.4 Boundary-scan Specific JTAG Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
25.5 Boundary-scan Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
25.6 ATmega164P-B/324P-B/644P-B Boundary-scan Order . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
25.7 Boundary-scan Description Language Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
25.8 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
26. Boot Loader Support – Read-While-Write Self-Programming . . . . . . . . . . . . . . . . . . 240
26.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
26.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
26.3 Application and Boot Loader Flash Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
26.4 Read-While-Write and No Read-While-Write Flash Sections . . . . . . . . . . . . . . . . . . . . . . . 241
26.5 Boot Loader Lock Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
26.6 Entering the Boot Loader Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
26.7 Addressing the Flash During Self-Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
26.8 Self-Programming the Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
26.9 Register Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
27. Memory Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
27.1 Program And Data Memory Lock Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
27.2 Fuse Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
27.3 Signature Bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
27.4 Calibration Byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
27.5 Page Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
27.6 Parallel Programming Parameters, Pin Mapping, and Commands . . . . . . . . . . . . . . . . . . . 259
27.7 Parallel Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
27.8 Serial Downloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
27.9 Serial Programming Instruction set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
27.10 Programming via the JTAG Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
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28. Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
28.1 Absolute Maximum Ratings* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
28.2 DC Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
28.3 Speed Grades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
28.4 Clock Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
28.5 System and Reset Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
28.6 External Interrupts Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
28.7 SPI Timing Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
28.8 2-wire Serial Interface Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
28.9 ADC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
29. Typical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
29.1 ATmega164P-B Typical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
29.2 ATmega324P-B Typical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
29.3 ATmega644P-B Typical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
30. Register Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
31. Instruction Set Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
32. Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
33. Packaging Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
34. Errata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
34.1 Errata for ATmega164P-B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
34.2 Errata for ATmega324P-B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
34.3 Errata for ATmega644P-B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
35. Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
36. Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
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Atmel Corporation
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