ATTINY102-SSFR [ATMEL]
RISC Microcontroller, CMOS,;
| 型号： | ATTINY102-SSFR |
| 厂家： | 
ATMEL |
| 描述： | RISC Microcontroller, CMOS, 时钟 ATM 异步传输模式 微控制器 光电二极管 外围集成电路 装置 |
| 文件： | 总255页 (文件大小：3713K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
8-bit AVR Microcontroller
ATtiny102 / ATtiny104
DATASHEET COMPLETE
Introduction
The Atmel® ATtiny102/ATtiny104 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 ATtiny102/ATtiny104 achieves
throughputs close to 1 MIPS per MHz. This empowers system designer to
optimize the device for power consumption versus processing speed.
Feature
®
®
High Performance, Low Power Atmel AVR 8-Bit Microcontroller Family
•
Advanced RISC Architecture
–
–
–
–
–
54 Powerful Instructions
Mostly Single Clock Cycle Execution
16 x 8 General Purpose Working Registers
Fully Static Operation
Up to 12 MIPS Throughput at 12MHz
•
Non-volatile Program and Data Memories
–
–
–
–
–
1024 Bytes of In-system Programmable Flash Program Memory
32 Bytes Internal SRAM
Flash Write/Erase Cycles: 10,000
Data Retention: 20 Years at 85°C / 100 Years at 25°C
Self-programming Flash on Full Operating Voltage Range (1.8 –
5.5V)
•
Peripheral Features
–
One 16-bit Timer/Counter (TC) with Prescaler, Input Capture,
Two Output Capture and Two PWM Channels
–
Programmable Watchdog Timer (WDT) with Separate On-chip
Oscillator
–
–
Selectable Internal Voltage References: 1.1V, 2.2V and 4.3V
10-bit ADC with 8-channels/14-pin and 5-channel/8-pin Package
Options
–
–
On-chip Analog Comparator (AC)
Serial Communication Module: USART
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
•
Special Microcontroller Features
–
In-system Programmable
•
•
External Programming (2.7 – 5.5V)
Self Programming (1.8 – 5.5V)
–
–
–
–
–
–
–
External and Internal Interrupt Sources
Low Power Idle, ADC Noise Reduction, and Power-pown Modes
Enhanced Power-on Reset Circuit
Programmable Supply Voltage Level Monitor with Interrupt and Reset
Accurate Internal Calibrated Oscillator
Fast and Normal Start-up Time Options Available
Individual Serial Number to Represent a Unique ID.
•
I/O and Packages
–
–
–
–
12 Programmable I/O Lines for ATtiny104 and 6 Programmable I/O Lines for ATtiny102
8-pin UDFN (ATtiny102)
8-pin SOIC150 (ATtiny102)
14-pin SOIC150 (ATtiny104)
•
•
•
Operating Voltage
1.8 - 5.5V
Temperature Range
-40 to +125°C
Speed Grades
–
–
–
–
–
0 – 4MHz at 1.8 – 5.5V
0 – 8MHz at 2.7 – 5.5V
0 – 12MHz at 4.5 – 5.5V
Atmel ATtiny102 / ATtiny104 [DATASHEET]
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Table of Contents
Introduction......................................................................................................................1
Feature............................................................................................................................ 1
1. Description.................................................................................................................8
2. Configuration Summary.............................................................................................9
3. Ordering Information ...............................................................................................10
4. Block Diagram..........................................................................................................11
5. Pin Configurations................................................................................................... 12
5.1. Pin Descriptions..........................................................................................................................12
6. I/O Multiplexing........................................................................................................14
7. General Information.................................................................................................15
7.1. Resources.................................................................................................................................. 15
7.2. Data Retention............................................................................................................................15
7.3. About Code Examples................................................................................................................15
8. AVR CPU Core........................................................................................................ 16
8.1. Overview.....................................................................................................................................16
8.2. Features..................................................................................................................................... 16
8.3. Block Diagram............................................................................................................................16
8.4. ALU – Arithmetic Logic Unit........................................................................................................18
8.5. Status Register...........................................................................................................................18
8.6. General Purpose Register File...................................................................................................18
8.7. The X-register, Y-register, and Z-register................................................................................... 19
8.8. Stack Pointer..............................................................................................................................19
8.9. Accessing 16-bit Registers.........................................................................................................20
8.10. Instruction Execution Timing...................................................................................................... 21
8.11. Reset and Interrupt Handling..................................................................................................... 21
8.12. Register Description...................................................................................................................22
9. AVR Memories.........................................................................................................27
9.1. Overview.....................................................................................................................................27
9.2. Features..................................................................................................................................... 27
9.3. In-System Reprogrammable Flash Program Memory................................................................27
9.4. SRAM Data Memory...................................................................................................................27
9.5. I/O Memory.................................................................................................................................29
10. Clock System...........................................................................................................30
10.1. Overview.....................................................................................................................................30
10.2. Clock Distribution........................................................................................................................30
10.3. Clock Subsystems......................................................................................................................30
10.4. Clock Sources............................................................................................................................ 31
10.5. System Clock Prescaler............................................................................................................. 32
10.6. Starting.......................................................................................................................................33
10.7. Register Description...................................................................................................................34
11. Power Management and Sleep Modes....................................................................39
11.1. Overview.....................................................................................................................................39
11.2. Features..................................................................................................................................... 39
11.3. Sleep Modes...............................................................................................................................39
11.4. Power Reduction Register..........................................................................................................40
11.5. Minimizing Power Consumption.................................................................................................41
11.6. Register Description...................................................................................................................42
12. SCRST - System Control and Reset....................................................................... 45
12.1. Overview.....................................................................................................................................45
12.2. Features..................................................................................................................................... 45
12.3. Resetting the AVR...................................................................................................................... 45
12.4. Reset Sources............................................................................................................................46
12.5. Watchdog Timer......................................................................................................................... 48
12.6. Register Description...................................................................................................................50
13. Interrupts................................................................................................................. 55
13.1. Overview.....................................................................................................................................55
13.2. Interrupt Vectors ........................................................................................................................55
13.3. External Interrupts......................................................................................................................56
13.4. Register Description...................................................................................................................57
14. I/O-Ports.................................................................................................................. 65
14.1. Overview.....................................................................................................................................65
14.2. Features..................................................................................................................................... 65
14.3. I/O Pin Equivalent Schematic.....................................................................................................65
14.4. Ports as General Digital I/O........................................................................................................66
14.5. Register Description...................................................................................................................79
15. USART - Universal Synchronous Asynchronous Receiver Transceiver..................89
15.1. Overview.....................................................................................................................................89
15.2. Features..................................................................................................................................... 89
15.3. Block Diagram............................................................................................................................89
15.4. Clock Generation........................................................................................................................90
15.5. Frame Formats...........................................................................................................................93
15.6. USART Initialization....................................................................................................................94
15.7. Data Transmission – The USART Transmitter........................................................................... 95
15.8. Data Reception – The USART Receiver.................................................................................... 97
15.9. Asynchronous Data Reception.................................................................................................100
15.10. Multi-Processor Communication Mode.................................................................................... 104
15.11. Examples of Baud Rate Setting............................................................................................... 105
15.12. Register Description.................................................................................................................108
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16. USARTSPI - USART in SPI Mode.........................................................................119
16.1. Overview...................................................................................................................................119
16.2. Features....................................................................................................................................119
16.3. Clock Generation......................................................................................................................119
16.4. SPI Data Modes and Timing.....................................................................................................120
16.5. Frame Formats.........................................................................................................................120
16.6. Data Transfer............................................................................................................................122
16.7. AVR USART MSPIM vs. AVR SPI............................................................................................123
16.8. Register Description.................................................................................................................123
17. TC0 - 16-bit Timer/Counter0 with PWM.................................................................124
17.1. Overview...................................................................................................................................124
17.2. Features................................................................................................................................... 124
17.3. Block Diagram..........................................................................................................................124
17.4. Definitions.................................................................................................................................125
17.5. Registers.................................................................................................................................. 126
17.6. Accessing 16-bit Timer/Counter Registers...............................................................................127
17.7. Timer/Counter Clock Sources.................................................................................................. 129
17.8. Counter Unit............................................................................................................................. 131
17.9. Input Capture Unit.................................................................................................................... 132
17.10. Output Compare Units............................................................................................................. 134
17.11. Compare Match Output Unit.....................................................................................................136
17.12. Modes of Operation..................................................................................................................137
17.13. Timer/Counter Timing Diagrams.............................................................................................. 145
17.14. Register Description.................................................................................................................146
18. AC - Analog Comparator....................................................................................... 160
18.1. Overview...................................................................................................................................160
18.2. Features................................................................................................................................... 160
18.3. Block Diagram..........................................................................................................................160
18.4. Register Description.................................................................................................................161
19. ADC - Analog to Digital Converter.........................................................................166
19.1. Overview...................................................................................................................................166
19.2. Features................................................................................................................................... 166
19.3. Block Diagram..........................................................................................................................166
19.4. Operation..................................................................................................................................167
19.5. Starting a Conversion...............................................................................................................168
19.6. Prescaling and Conversion Timing...........................................................................................169
19.7. Changing Channel or Reference Selection..............................................................................172
19.8. ADC Input Channels.................................................................................................................172
19.9. ADC Voltage Reference........................................................................................................... 172
19.10. ADC Noise Canceler................................................................................................................173
19.11. Analog Input Circuitry...............................................................................................................173
19.12. Analog Noise Canceling Techniques........................................................................................174
19.13. ADC Accuracy Definitions........................................................................................................174
19.14. ADC Conversion Result........................................................................................................... 176
19.15. Register Description.................................................................................................................176
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20. MEMPROG- Memory Programming......................................................................185
20.1. Overview...................................................................................................................................185
20.2. Features................................................................................................................................... 185
20.3. Non-Volatile Memories (NVM)..................................................................................................186
20.4. Accessing the NVM..................................................................................................................191
20.5. Self programming.....................................................................................................................194
20.6. External Programming..............................................................................................................194
20.7. Register Description.................................................................................................................195
21. TPI-Tiny Programming Interface............................................................................198
21.1. Overview...................................................................................................................................198
21.2. Features................................................................................................................................... 198
21.3. Block Diagram..........................................................................................................................198
21.4. Physical Layer of Tiny Programming Interface.........................................................................199
21.5. Instruction Set...........................................................................................................................203
21.6. Accessing the Non-Volatile Memory Controller........................................................................ 205
21.7. Control and Status Space Register Descriptions..................................................................... 206
22. Electrical Characteristics ...................................................................................... 210
22.1. Absolute Maximum Ratings*.................................................................................................... 210
22.2. DC Characteristics....................................................................................................................210
22.3. Speed.......................................................................................................................................212
22.4. Clock Characteristics................................................................................................................213
22.5. System and Reset Characteristics........................................................................................... 214
22.6. Analog Comparator Characteristics..........................................................................................215
22.7. ADC Characteristics ................................................................................................................216
22.8. Serial Programming Characteristics.........................................................................................217
23. Typical Characteristics...........................................................................................218
23.1. Active Supply Current...............................................................................................................218
23.2. Idle Supply Current...................................................................................................................221
23.3. Supply Current of I/O Modules.................................................................................................222
23.4. Power-down Supply Current.....................................................................................................223
23.5. Pin Driver Strength...................................................................................................................224
23.6. Pin Threshold and Hysteresis...................................................................................................228
23.7. Analog Comparator Offset........................................................................................................232
23.8. Pin Pull-up................................................................................................................................233
23.9. Internal Oscillator Speed..........................................................................................................236
23.10. VLM Thresholds.......................................................................................................................238
23.11. Current Consumption of Peripheral Units.................................................................................240
23.12. Current Consumption in Reset and Reset Pulsewidth.............................................................243
24. Register Summary.................................................................................................244
24.1. Note..........................................................................................................................................245
25. Instruction Set Summary....................................................................................... 246
26. Packaging Information...........................................................................................250
26.1. 8-pin UDFN...............................................................................................................................250
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26.2. 8-pin SOIC150..........................................................................................................................251
26.3. 14-pin SOIC150........................................................................................................................252
27. Errata.....................................................................................................................253
27.1. ATtiny102..................................................................................................................................253
27.2. ATtiny104..................................................................................................................................253
28. Datasheet Revision History................................................................................... 254
28.1. Rev D - 10/2016....................................................................................................................... 254
28.2. Rev C - 07/2016....................................................................................................................... 254
28.3. Rev B - 06/2016........................................................................................................................254
28.4. Rev A - 02/2016........................................................................................................................254
Atmel ATtiny102 / ATtiny104 [DATASHEET]
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1.
Description
®
®
The Atmel AVR core combines a rich instruction set with 16 general purpose working registers. All the
16 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.
The device provides the following features: 1024 Bytes of In-System Programmable Flash with Read-
While-Write capabilities, 32 Bytes SRAM, 6/12 general purpose I/O lines for ATtiny102/ATtiny104, 16
general purpose working registers, a 16-bit Timer/Counters (TC) with compare modes, internal and
external interrupts, one serial programmable USART, a programmable Watchdog Timer with internal
Oscillator and three software selectable power saving modes. The Idle mode stops the CPU while
allowing the SRAM, TC, USART, ADC, Analog Comparator (AC), and interrupt system to continue
functioning. ADC Noise Reduction mode minimizes switching noise during ADC conversions by stopping
the CPU and all I/O modules except the ADC. The Power-down mode saves the register contents but
freezes the Oscillator, disabling all other chip functions until the next interrupt or hardware reset.
The device is manufactured using Atmel’s high density Non-Volatile Memory (NVM) technology. The on-
chip, in-system programmable Flash allows program memory to be re-programmed in-system by a
conventional, NVM programmer.
The device 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 kit.
Atmel ATtiny102 / ATtiny104 [DATASHEET]
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Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
2.
Configuration Summary
ATtiny102
ATtiny104
Pin Count
8
14
1024
32
-
Flash (Bytes)
1024
SRAM (Bytes)
32
-
EEPROM (Bytes)
General Purpose I/O-pins (GPIOs)
USART
6
12
1
1
Analog-to-Digital Converter (ADC) / Channels
10-bit ADC with 5-channel 10-bit ADC with 8-channels
Analog Comparators (AC) Channels
AC Propagation Delay
16-bit Timer Counter (TC) Instances
PWM Channels
1
1
75-750ns
1
75-750ns
1
2
2
RC Oscillator
+/-2 %
+/-2 %
Internal Voltage Reference
Operating Voltage
1.1V/2.2V/4.3V
1.8 - 5.5V
12
1.1V/2.2V/4.3V
Max Operating Frequency (MHz)
Temperature Range
-40°C to +125°C
8-pin UDFN
8-pin SOIC150
Packages
14-pin SOIC150
Atmel ATtiny102 / ATtiny104 [DATASHEET]
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Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
3.
Ordering Information
Speed [MHz] Power Supply [V]
Ordering Code
Package
Operational Range
12 1.8 -5.5
ATtiny102-M7R
8 pad UDFN
Industrial (-40°C to +105°C)
ATtiny102F-M7R(1)
ATtiny102-SSNR
ATtiny102F-SSNR(1)
ATtiny104-SSNR
ATtiny104F-SSNR(1)
ATtiny102-M8R
8 pad UDFN
8 pin SOIC150
8 pin SOIC150
14 pin SOIC150
14 pin SOIC150
8 pad UDFN
Industrial (-40°C to +125°C)
ATtiny102F-M8R(1)
ATtiny102-SSFR
ATtiny102F-SSFR(1)
ATtiny104-SSFR
ATtiny104F-SSFR(1)
8 pad UDFN
8 pin SOIC150
8 pin SOIC150
14 pin SOIC150
14 pin SOIC150
Note:ꢀ
1. ATtiny104F-xxx and ATtiny102F-xxx have the fast start-up time option.
Package Type
8 pad UDFN 8-pad, 2 x 3 x 0.6mm Body, Thermally Enhanced Plastic Ultra Thin Dual Flat No-Lead Package (UDFN)
8 pin
8-lead, 0.150” Wide Body, Plastic Gull Wing Small Outline (JEDEC SOIC)
SOIC150
14 pin
14-lead, 1.27mm Pitch, 8.65 x 3.90 x 1.60mm Body Size, Plastic Small Outline Package (SOIC)
SOIC150
Related Links
Starting from Reset on page 33
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4.
Block Diagram
Figure 4-1.ꢀBlock Diagram
SRAM
FLASH
CPU
Clock generation
Power
management
and clock
control
8MHz Calib Osc
External clock
PA[7:0]
PB[3:0]
I/O
PORTS
128 kHz Internal Osc
PCINT[11:0]
INT0
D
A
T
A
B
U
S
Interrupt
ADC
Vcc
Watchdog
Timer
ADC[7:0]
Vcc
Power
Supervision
POR & RESET
RESET
GND
AIN0
Internal
Reference
AIN1
ACO
ACPMUX
AC
RxD0
TxD0
XCK0
OC0A/B
T0
ICP0
TC 0
USART 0
(16-bit)
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5.
Pin Configurations
Figure 5-1.ꢀPin-Out of 8-Pin UDFN
Caution:ꢀ The thermal pad on the rear of the package should not be connected.
Figure 5-2.ꢀPin-Out of 8-Pin SOIC150
VCC
1
2
3
4
8
7
6
5
GND
(PCINT0/T0/CLKI/AIN0/ADC0/TPICLK) PA0
(PCINT1/OC0B/AIN1/ADC1/TPIDATA ) PA1
(PCINT2/RESET) PA2
PB3 (ADC7/T0/RxD0/ACO/PCINT11)
PB2 (ADC6/ICP0/TxD0/PCINT10)
PB1 (ADC5/CLKO/INT0/OC0A/PCINT9)
Figure 5-3.ꢀPin-Out of 14-Pin SOIC150
VCC
(PCINT0/T0/CLKI/AN0/ADC0/TPICLK) PA0
(PCINT1/OC0B/AIN1/ADC1/TPIDATA ) PA1
(PCINT2/RESET) PA2
1
2
3
4
5
6
7
14
13
12
11
10
9
GND
PB3 (ADC7/ACO/RxD0/T0*/PCINT11)
PB2 (ADC6/ICP0/TxD0/PCINT10)
PB1 (ADC5/CLKO/INT0/OC0A/PCINT9)
PB0 (ADC4/PCINT8)
(PCINT3/OC0A*) PA3
(PCINT4/ICP0*) PA4
PA7 (PCINT7)
(PCINT5/OC0B*/ADC2) PA5
8
PA6 (ADC3/PCINT6)
Power
Programming
Ext clock
Digital
Analog
Ground
5.1.
Pin Descriptions
5.1.1.
VCC
Digital supply voltage.
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5.1.2.
5.1.3.
GND
Ground.
Port A (PA[7:0])
This is a 8-bit, bi-directional I/O port with internal pull-up resistors, individually selectable for each bit. The
output buffers have symmetrical drive characteristics, with both high sink and source capability. As inputs,
the port pins that are externally pulled low will source current if pull-up resistors are activated. Port pins
are tri-stated when a reset condition becomes active, even if the clock is not running.
5.1.4.
5.1.5.
Port B (PB[3:0])
This is a 4-bit, bi-directional I/O port with internal pull-up resistors, individually selectable for each bit. The
output buffers have symmetrical drive characteristics, with both high sink and source capability. As inputs,
the port pins that are externally pulled low will source current if pull-up resistors are activated. Port pins
are tri-stated when a reset condition becomes active, even if the clock is not running.
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 and provided the reset pin has not been disabled. The minimum pulse length is
given in System and Reset Characteristics of Electrical Characteristics. Shorter pulses are not
guaranteed to generate a reset.
The reset pin can also be used as a (weak) I/O pin.
Related Links
System and Reset Characteristics on page 214
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6.
I/O Multiplexing
Each pin is by default controlled by the PORT as a general purpose I/O and alternatively it can be
assigned to one of the peripheral functions. The following table describes the peripheral signals
multiplexed to the PORT I/O pins.
Table 6-1.ꢀPORT Function Multiplexing
(3)
(3)
(8)
14-pin 8-pin Pin name
Special INT
ADC
AC
USART Timer Programming
(1)
1
1
2
3
4
-
V
CC
(2)
(5)
2
PA[0]
PA[1]
PA[2]
PA[3]
PA[4]
PA[5]
PA[6]
PA[7]
PB[0]
PB[1]
PB[2]
PB[3]
GND
CLKI
PCINT0
PCINT1
ADC0
ADC1
AIN0
AIN1
T0
TPICLK
3
OC0B TPIDATA
RESET
4
RESET PCINT2
PCINT3
(9)
5
OC0A
(9)
6
-
PCINT4
ICP0
(5)(9)
7
-
PCINT5
ADC2
ADC3
OC0B
8
-
PCINT6
9
-
PCINT7
10
11
12
13
14
-
PCINT8
ADC4
(6)
5
6
7
8
CLKO
PCINT9/INT0 ADC5
XCK0
TxD0
OC0A
ICP0
T0
(7)
PCINT10
PCINT11
ADC6
ADC7
(4)(9)
ACO RxD0
Note:ꢀ
1. On the 8-pin UDFN package, the thermal pad should not be connected as well.
2. Priority of CLKI is higher than ADC0. When EXT_CLK is enabled, ADC channel will not work and
DIDR0 will not disable the digital input buffer.
3. When both PCINT and the corresponding ADC channel are enabled, the digital input buffer will not
be disabled.
4. When ACO is enabled, ADC, TC and USART RX inputs are not disabled.
5. When OC0B is enabled, ADC and AC will continue to receive inputs on that channel if enabled.
6. When CLKO is enable in PB[1], OCA will get lower priority.
7. When USART is enabled, the users must ensure that ADC channel corresponding to the TxD0 pin
is not used. Because DIDR0 register will only control the input buffer, not the output part.
8. During reset/external programming, all pins are treated as inputs and outputs are disabled.
9. Alternative location when enabling T/C Remap
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7.
General Information
7.1.
Resources
A comprehensive set of development tools, application notes, and datasheets are available for download
on http://www.atmel.com/avr.
7.2.
7.3.
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.
About Code Examples
This documentation contains simple code examples that briefly show how to use various parts of the
device. These code examples assume that the part specific header file is included before compilation. Be
aware that not all C compiler vendors include bit definitions in the header files and interrupt handling in C
is compiler dependent. Confirm with the C compiler documentation for more details.
Related Links
Reset and Interrupt Handling on page 21
Code Examples on page 50
Atmel ATtiny102 / ATtiny104 [DATASHEET]
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Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
8.
AVR CPU Core
8.1.
Overview
®
®
The Atmel AVR core combines a rich instruction set with 16 general purpose working registers. All the
16 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.
8.2.
Features
•
•
•
•
•
•
Advanced RISC Architecture
54 Powerful Instructions
Mostly Single Clock Cycle Execution
16 x 8 General Purpose Working Registers
Fully Static Operation
Up to 12 MIPS Throughput at 12MHz
8.3.
Block Diagram
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.
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Figure 8-1.ꢀBlock Diagram of the AVR Architecture
Program
counter
Register file
Flash program
memory
R31 (ZH)
R29 (YH)
R27 (XH)
R25
R30 (ZL)
R28 (YL)
R26 (XL)
R24
R23
R22
R21
R20
R19
R17
R18
R16
Instruction
register
Instruction
decode
Data memory
Stack
pointer
Status
register
ALU
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 16 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 16 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 but 32-bit wide
instructions also exist. The actual instruction set varies, as some devices only implement a part of the
instruction set.
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 four 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 as the data space locations, 0x0000 - 0x003F.
See Instruction Set Summary section for a detailed description.
8.4.
ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 16 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 Instruction Set
Summary section for a detailed description.
8.5.
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. 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.
8.6.
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
One 16-bit output operand and one 16-bit result input
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Figure 8-2.ꢀAVR CPU General Purpose Working Registers
7
0
R16
R17
R18
…
General
Purpose
Working
Registers
R26
R27
R28
R29
R30
R31
X-register Low Byte
X-register High Byte
Y-register Low Byte
Y-register High Byte
Z-register Low Byte
Z-register High Byte
Note:ꢀ A typical implementation of the AVR register file includes 32 general purpose registers but
ATtiny102/ATtiny104 implement only 16 registers. For reasons of compatibility the registers are numbered
R16...R31, not R0...R15.
Most of the instructions operating on the Register File have direct access to all registers, and most of
them are single cycle instructions.
8.7.
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 the figure.
Figure 8-3.ꢀThe X-, Y-, and Z-registers
15
XH
XL
0
0
X-register
7
0
0
7
7
R27
YH
R26
YL
15
7
0
0
Y-register
R29
ZH
R28
ZL
15
7
0
0
Z-register
0
7
R31
R30
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).
8.8.
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. The Stack is implemented as growing from higher to
lower memory locations. The Stack Pointer Register always points to the top of the Stack, and the Stack
Pointer must be set to point above 0x40.
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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 the table for Stack Pointer details.
Table 8-1.ꢀStack Pointer Instructions
Instruction Stack pointer
Description
PUSH
Decremented by 1 Data is pushed onto the stack
Decremented by 2 Return address is pushed onto the stack with a subroutine call or
interrupt
ICALL
RCALL
POP
Incremented by 1 Data is popped from the stack
Incremented by 2 Return address is popped from the stack with return from subroutine or
return from interrupt
RET
RETI
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. 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.
Related Links
SPL and SPH on page 24
SRAM Data Memory on page 27
8.9.
Accessing 16-bit Registers
The AVR data bus is 8 bits wide, and so accessing 16-bit registers requires atomic operations. These
registers must be byte-accessed using two read or write operations. 16-bit registers are connected to the
8-bit bus and a temporary register using a 16-bit bus.
For a write operation, the low byte of the 16-bit register must be written before the high byte. The low byte
is then written into the temporary register. When the high byte of the 16-bit register is written, the
temporary register is copied into the low byte of the 16-bit register in the same clock cycle.
For a read operation, the low byte of the 16-bit register must be read before the high byte. When the low
byte 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. When the high byte is read, it is then read from the
temporary register.
This ensures that the low and high bytes of 16-bit registers are always accessed simultaneously when
reading or writing the register.
Interrupts can corrupt the timed sequence if an interrupt is triggered and accesses the same 16-bit
register during an atomic 16-bit read/write operation. To prevent this, interrupts can be disabled when
writing or reading 16-bit registers.
The temporary registers can also be read and written directly from user software.
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8.10. 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. The Figure below 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 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
Figure 8-4.ꢀ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
The following Figure 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 8-5.ꢀSingle Cycle ALU Operation
T1
T2
T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
8.11. 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.
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 Interrupts. They have determined priority levels: The
lower the address the higher is the priority level. RESET has the highest priority, and next is INT0 – the
External Interrupt Request 0.
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
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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.
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.
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)
Note:ꢀ See Code Examples
Related Links
Interrupts on page 55
8.11.1. Interrupt Response Time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles minimum. After
four clock cycles the program vector address for the actual interrupt handling routine is executed. During
this four 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 four 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 four clock cycles. During these four clock cycles, the Program Counter
(two bytes) is popped back from the Stack, the Stack Pointer is incremented by two, and the I-bit in SREG
is set.
8.12. Register Description
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8.12.1. Configuration Change Protection Register
Name:ꢀ CCP
Offset:ꢀ 0x3C
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
0
5
0
4
0
3
0
2
0
1
0
0
0
CCP[7:0]
Access
Reset
0
Bits 7:0 – CCP[7:0]:ꢀConfiguration Change Protection
In order to change the contents of a protected I/O register, the CCP register must first be written with the
correct signature. After CCP is written, the protected I/O registers may be written to during the next four
CPU instruction cycles. All interrupts are ignored during these cycles. After these cycles interrupts are
automatically handled again by the CPU, and any pending interrupts will be executed according to their
priority.
When the protected I/O register signature is written, CCP[0] will read as one as long as the protected
feature is enabled, while CCP[7:1] will always read as zero.
When the NVM self-programming signature is written, CCP[1] will read as one for four CPU instruction
cycles , other bits will read as zero and CCP[1] will be cleared automatically after four cycles. The
software should write data to flash high byte within this four clock cycles to execute self-programming.
Table 8-2.ꢀSignatures Recognized by the Configuration Change Protection Register
Signature
0xD8
Group
Description
IOREG: CLKMSR, CLKPSR, WDTCSR
SPM
Protected I/O register
NVM self-programming enable
0xE7
Note:ꢀ Bit 0 and 1 have R/W access. The other bits only have W access.
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8.12.2. Stack Pointer Register Low and High byte
The SPL and SPH register pair represents the 16-bit value, SP.The low byte [7:0] (suffix L) is accessible
at the original offset. The high byte [15:8] (suffix H) can be accessed at offset + 0x01. For more details on
reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
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 offset
addresses.
Name:ꢀ SPL and SPH
Offset:ꢀ 0x3D
Reset:ꢀ 0x5F
Property: -
ꢀ
Bit
15
14
13
12
11
10
9
8
Access
Reset
R
0
R
0
R
0
R
0
R
0
R
0
Bit
7
6
SP6
RW
1
5
SP5
RW
0
4
SP4
RW
1
3
SP3
RW
1
2
SP2
RW
1
1
SP1
RW
1
0
SP0
RW
1
Access
Reset
Bits 0, 1, 2, 3, 4, 5, 6 – SPn:ꢀStack Pointer Register
SPL and SPH are combined into SP.
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8.12.3. Status Register
When addressing I/O Registers as data space using LD and ST instructions, the provided offset must be
used. When using the I/O specific commands IN and OUT, the offset is reduced by 0x20, resulting in an
I/O address offset within 0x00 - 0x3F.
Name:ꢀ SREG
Offset:ꢀ 0x5F
Reset:ꢀ 0x00
Property: When addressing as I/O Register: address offset is 0x3F
ꢀ
Bit
7
I
6
T
5
H
4
S
3
V
2
N
1
Z
0
C
Access
Reset
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:ꢀ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.
Bit 5 – H:ꢀHalf Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Flag is useful in
BCD arithmetic. See the Instruction Set Description for detailed information.
Bit 4 – S:ꢀSign Flag, S = N ㊉ 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 arithmetic. 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.
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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.
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9.
AVR Memories
9.1.
Overview
This section describes the different memory types in the device. The AVR architecture has two main
memory spaces, the Data Memory and the Program Memory space. All memory spaces are linear and
regular.
9.2.
Features
•
•
•
•
•
•
Non-volatile Program and Data Memories
1024 Bytes of In-system Programmable Flash Program Memory
32 Bytes Internal SRAM
Flash Write/Erase Cycles: 10,000
Data Retention: 20 Years at 85°C / 100 Years at 25°C
Self-programming Flash on Full Operating Voltage Range (1.8 – 5.5V)
9.3.
In-System Reprogrammable Flash Program Memory
The ATtiny102/ATtiny104 contains 1024 Bytes 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 512 x 16.
The device Program Counter (PC) is 9 bits wide, thus addressing the 512 program memory locations,
starting at 0x000. Memory Programming contains a detailed description on Flash data serial downloading.
Constant tables can be allocated within the entire address space of program memory by using load/store
instructions. Since program memory can not be accessed directly, it has been mapped to the data
memory. The mapped program memory begins at byte address 0x4000 in data memory. Although
programs are executed starting from address 0x000 in program memory it must be addressed starting
from 0x4000 when accessed via the data memory.
Timing diagrams of instruction fetch and execution are presented in Instruction Execution Timing section.
Related Links
Instruction Execution Timing on page 21
MEMPROG- Memory Programming on page 185
9.4.
SRAM Data Memory
Data memory locations include the I/O memory, the internal SRAM memory, the Non-Volatile Memory
(NVM) Lock bits, and the Flash memory. The following figure shows how the ATtiny102/ATtiny104 SRAM
Memory is organized.
The first 64 locations are reserved for I/O memory, while the following 32 data memory locations address
the internal data SRAM.
The Non-Volatile Memory (NVM) Lock bits and all the Flash memory sections are mapped to the data
memory space. These locations appear as read-only for device firmware.
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The four different addressing modes for data memory are direct, indirect, indirect with pre-decrement, and
indirect with post-increment. In the register file, registers R26 to R31 function as pointer registers for
indirect addressing.
The IN and OUT instructions can access all 64 locations of I/O memory. Direct addressing using the LDS
and STS instructions reaches the 128 locations between 0x0040 and 0x00BF.
The indirect addressing reaches the entire data memory space. When using indirect addressing modes
with automatic pre-decrement and post-increment, the address registers X, Y, and Z are decremented or
incremented.
Figure 9-1.ꢀData Memory Map (Byte Addressing)
I/O SPACE
SRAM DATA MEMORY
(reserved)
0x0000 ... 0x003F
0x0040 ... 0x005F
0x0060 ... 0x3EFF
0x3F00 ... 0x3F01
0x3F02 ... 0x3F3F
0x3F40 ... 0x3F41
0x3F42 ... 0x3F7F
0x3F80 ... 0x3F81
0x3F82 ... 0x3FBF
0x3FC0 ... 0x3FC3
0x3FC4 ... 0x3FFF
NVM LOCK BITS
(reserved)
CONFIGURATION BITS
(reserved)
CALIBRATION BITS
(reserved)
DEVICE ID BITS
(reserved)
FLASH PROGRAM MEMORY 0x4000 ... 0x41FF/0x43FF
(reserved) 0x4400 ... 0xFFFF
9.4.1.
Data Memory Access Times
The internal data SRAM access is performed in two clkCPU cycles as described in the following Figure.
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Figure 9-2.ꢀOn-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address valid
Compute Address
Address
Data
WR
Data
RD
Memory Access Instruction
Next Instruction
9.5.
I/O Memory
The I/O space definition of the device is shown in the Register Summary.
All ATtiny102/ATtiny104 I/Os and peripherals are placed in the I/O space. All I/O locations may be
accessed by the LD and ST instructions, transferring data between the 16 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, except USART registers. In these registers, the value of single bits
can be checked by using the SBIS and SBIC instructions. Refer to the Instruction Set Summary section
for more details.
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 '1' to them; this is described in the flag descriptions.
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 0x00-0x1F only.
The I/O and Peripherals Control Registers are explained in later sections.
Related Links
Register Summary on page 244
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10.
Clock System
10.1. Overview
This chapter summarizes the clock distribution and terminology in the ATtiny102/ATtiny104 device.
10.2. Clock Distribution
All 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 the section on
Power Management and Sleep Modes. The clock systems are detailed below.
Figure 10-1.ꢀClock Distribution
ANALOG-TO-DIGITAL
CONVERTER
GENERAL
I/O MODULES
CPU
CORE
RAM
NVM
clkADC
clkI/O
clkNVM
clkCPU
CLOCK CONTROL UNIT
SOURCE CLOCK
RESET
LOGIC
WATCHDOG
CLOCK
WATCHDOG
TIMER
CLOCK
PRESCALER
CLOCK
SWITCH
EXTERNAL
CLOCK
WATCHDOG
OSCILLATOR
CALIBRATED
OSCILLATOR
Related Links
Power Management and Sleep Modes on page 39
10.3. Clock Subsystems
10.3.1. 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 System Registers and the SRAM data memory.
Halting the CPU clock inhibits the core from performing general operations and calculations.
10.3.2. I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counter. 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.
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10.3.3. NVM Clock – clkNVM
The NVM clock controls operation of the Non-Volatile Memory Controller. The NVM clock is usually active
simultaneously with the CPU clock.
10.3.4. 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.
10.4. Clock Sources
The device has the following clock source options, selectable by Clock Main Select Bits in Clock Main
Settings Register (CLKMSR.CLKMS). All synchronous clock signals are derived from the main clock. The
three alternative sources for the main clock are as follows:
•
•
•
Calibrated Internal 8MHz Oscillator
External Clock
Internal 128kHz Oscillator.
Refer to description of Clock Main Select Bits in Clock Main Settings Register (CLKMSR.CLKMS) for how
to select and change the active clock source.
10.4.1. Calibrated Internal 8MHz Oscillator
The calibrated internal oscillator provides an approximately 8MHz clock signal. Though voltage and
temperature dependent, this clock can be very accurately calibrated by the user.
During reset, hardware loads the calibration byte into the Oscillator Calibration Register (OSCCAL)
register and thereby automatically calibrates the oscillator. The accuracy of this calibration is shown as
Factory calibration in Accuracy of Calibrated Internal Oscillator of Electrical Characteristics chapter.
When this oscillator is used as the main clock, the watchdog oscillator will still be used for the watchdog
timer and reset time-out. For more information on the pre-programmed calibration value, see section
Calibration Section.
It is possible to reach higher accuracies than factory defaults, especially when the application allows
temperature and voltage ranges to be narrowed. The firmware can reprogram the calibration data in
OSCCAL either at start-up or during run-time. The continuous, run-time calibration method allows
firmware to monitor voltage and temperature and compensate for any detected variations.
When this oscillator is used as the chip clock, it will still be used for the Watchdog Timer and for the Reset
Time-out.
Related Links
Calibration Section on page 191
Accuracy of Calibrated Internal Oscillator on page 213
Internal Oscillator Speed on page 236
10.4.2. External Clock
To drive the device from an external clock source, CLKI should be driven as shown in the Figure below.
To run the device on an external clock, the CLKMSR.CLKMS must be programmed to '0b10'.
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Table 10-1.ꢀExternal Clock Frequency
Frequency
CLKMSR.CLKMS
0 - 12MHz
0b10
Figure 10-2.ꢀExternal Clock Drive Configuration
EXTERNAL
CLOCK
EXTCLK
GND
SIGNAL
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. It is required to ensure that the MCU is kept in Reset during the
changes.
10.4.3. Internal 128kHz Oscillator
The internal 128kHz oscillator is a low power oscillator providing a clock of 128kHz. The frequency
depends on supply voltage, temperature and batch variations. This clock may be select as the main clock
by setting the CLKMSR.CLKMS to 0b01.
10.4.4. Switching Clock Source
The main clock source can be switched at run-time using the CLKMSR – Clock Main Settings Register.
When switching between any clock sources, the clock system ensures that no glitch occurs in the main
clock.
10.4.5. Default Clock Source
The calibrated internal 8MHz oscillator is always selected as main clock when the device is powered up
or has been reset. The synchronous system clock is the main clock divided by 8, controlled by the
System Clock Prescaler. The Clock Prescaler Select Bits in Clock Prescale Register (CLKPSR.CLKPS)
can be written later to change the system clock frequency. See section “System Clock Prescaler”.
10.5. System Clock Prescaler
The system clock is derived from the main clock via the System Clock Prescaler. The system clock can
be divided by setting the “CLKPSR – Clock Prescale Register”. The system clock prescaler can be used
to decrease power consumption at times when requirements for processing power is low or to bring the
system clock within limits of maximum frequency. The prescaler can be used with all main clock source
options, and it will affect the clock frequency of the CPU and all synchronous peripherals.
The System Clock Prescaler can be used to implement run-time changes of the internal clock frequency
while still ensuring stable operation.
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10.5.1. Switching Prescaler Setting
When switching between prescaler settings, the system clock prescaler ensures that no glitch occurs in
the system clock and that no intermediate frequency is higher than neither the clock frequency
corresponding the previous setting, nor the clock frequency corresponding to the new setting.
The ripple counter that implements the prescaler runs at the frequency of the main 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 another cannot be
exactly predicted.
From the time the CLKPSR.CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before the
new clock frequency is active. In this interval, two active clock edges are produced. Here, T1 is the
previous clock period, and T2 is the period corresponding to the new prescaler setting.
10.6. Starting
10.6.1. Starting from Reset
The internal reset is immediately asserted when a reset source goes active. The internal reset is kept
asserted until the reset source is released and the start-up sequence is completed. The start-up
sequence includes three steps, as follows.
1. The first step after the reset source has been released consists of the device counting the reset
start-up time. The purpose of this reset start-up time is to ensure that supply voltage has reached
sufficient levels. The reset start-up time is counted using the internal 128kHz oscillator.
Note:ꢀ The actual supply voltage is not monitored by the start-up logic. The device will count until
the reset start-up time has elapsed even if the device has reached sufficient supply voltage levels
earlier.
2. The second step is to count the oscillator start-up time, which ensures that the calibrated internal
oscillator has reached a stable state before it is used by the other parts of the system. The
calibrated internal oscillator needs to oscillate for a minimum number of cycles before it can be
considered stable.
3. The last step before releasing the internal reset is to load the calibration and the configuration
values from the Non-Volatile Memory to configure the device properly. The configuration time is
listed in the next table.
There are two start-up time options which will be supported :
•
•
Normal start-up time: 64ms
Fast start-up time: 8ms
Table 10-2.ꢀStart-up Times when Using the Internal Calibrated Oscillator with Normal start-up time
Reset Oscillator Configuration
64ms 6cycles 21cycles
Total start-up time
64ms + 6 oscillator cycles + 21 system clock cycles (1)
Table 10-3.ꢀStart-up Times when Using the Internal Calibrated Oscillator with shorter startup time
Reset Oscillator
Configuration
Total start-up time
8ms
6cycles
21cycles
8 ms + 6 oscillator cycles + 21 system clock cycles (1)
Note:ꢀ
1. After powering up the device or after a reset the system clock is automatically set to calibrated
internal 8MHz oscillator, divided by 8
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10.6.2. Starting from Power-Down Mode
When waking up from Power-Down sleep mode, the supply voltage is assumed to be at a sufficient level
and only the oscillator start-up time is counted to ensure the stable operation of the oscillator. The
oscillator start-up time is counted on the selected main clock, and the start-up time depends on the clock
selected.
Table 10-4.ꢀStart-up Time from Power-Down Sleep Mode.
Oscillator start-up time
Total start-up time
6 cycles
6 oscillator cycles (1)
Note:ꢀ 1. The start-up time is measured in main clock oscillator cycles.
10.6.3. Starting from Idle / ADC Noise Reduction / Standby Mode
When waking up from Idle, ADC Noise Reduction or Standby Mode, the oscillator is already running and
no oscillator start-up time is introduced.
10.7. Register Description
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10.7.1. Clock Main Settings Register
Name:ꢀ CLKMSR
Offset:ꢀ 0x37
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
CLKMS[1:0]
Access
Reset
R/W
0
R/W
0
Bits 1:0 – CLKMS[1:0]:ꢀClock Main Select Bits
These bits select the main clock source of the system. The bits can be written at run-time to switch the
source of the main clock. The clock system ensures glitch free switching of the main clock source.
Table 10-5.ꢀSelection of Main Clock
CLKM
00
Main Clock Source
Calibrated Internal 8MHz Oscillator
Internal 128kHz Oscillator (WDT Oscillator)
External clock
01
10
11
Reserved
To avoid unintentional switching of main clock source, a protected change sequence must be followed to
change the CLKMS bits, as follows:
1. Write the signature for change enable of protected I/O register to register CCP.
2. Within four instruction cycles, write the CLKMS bits with the desired value.
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10.7.2. Oscillator Calibration Register
Name:ꢀ OSCCAL
Offset:ꢀ 0x39
Reset:ꢀ xxxxxxxx
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
CAL[7:0]
Access
Reset
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
Bits 7:0 – CAL[7:0]:ꢀ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 Accuracy of
Calibrated Internal Oscillator section of Electrical Characteristics chapter.
The application software can write this register to change the oscillator frequency. The oscillator can be
calibrated to frequencies as specified in Accuracy of Calibrated Internal Oscillator section of Electrical
Characteristics chapter. Calibration outside that range is not guaranteed.
The lowest oscillator frequency is reached by programming these bits to zero. Increasing the register
value increases the oscillator frequency.
Note that this oscillator is used to time Flash write accesses, and write times will be affected accordingly.
Do not calibrate to more than 8.8MHz if Flash is to be written. Otherwise, the Flash write may fail.
To ensure stable operation of the MCU the calibration value should be changed in small steps. A step
change in frequency of more than 2% from one cycle to the next can lead to unpredictable behavior. Also,
the difference between two consecutive register values should not exceed 0x20. If these limits are
exceeded the MCU must be kept in reset during changes to clock frequency.
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10.7.3. Clock Prescaler Register
Name:ꢀ CLKPSR
Offset:ꢀ 0x36
Reset:ꢀ 0x00000011
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
CLKPS[3:0]
Access
Reset
R/W
0
R/W
0
R/W
1
R/W
1
Bits 3:0 – CLKPS[3:0]:ꢀClock Prescaler Select
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 the table below.
Table 10-6.ꢀClock Prescaler Select
CLKPS[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
Clock Division Factor
1
2
4
8 (default)
16
32
64
128
1000
1001
1010
1011
1100
1101
1110
256
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
1111
To avoid unintentional changes of clock frequency, a protected change sequence must be followed to
change the CLKPS bits:
1. Write the signature for change enable of protected I/O register to register CCP
2. Within four instruction cycles, write the desired value to CLKPS bits
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At start-up, CLKPS bits are reset to 0b0011 to select the clock division factor of 8. If the selected clock
source has a frequency higher than the maximum allowed the application software must make sure a
sufficient division factor is used. To make sure the write procedure is not interrupted, interrupts must be
disabled when changing prescaler settings.
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11.
Power Management and Sleep Modes
11.1. Overview
The high performance and industry leading code efficiency makes the AVR microcontrollers an ideal
choise for low power applications. In addition, 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.
11.2. Features
•
Minimizing Power Consumption
•
Sleep modes:
–
–
–
–
Idle
ADC Noise Reduction Mode
Power-Down Mode
Standby Mode
11.3. Sleep Modes
The following Table shows the different sleep modes and their wake up
Table 11-1.ꢀActive Clock Domains and Wake-up Sources in the Different Sleep Modes.
Active Clock Domains
Oscillators
Main Clock
Wake-up Sources
INT0 and Pin
Sleep Mode clk
clk
NVM
clk
IO
clk
ADC
ADC Other I/O Watchdog
Interrupt
VLM Interrupt
CPU
Source Enabled Change
Idle
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes Yes
Yes
Yes
Yes
Yes
Yes
(1)
ADC Noise
Reduction
(1)
(1)
Standby
Yes
Yes
Yes
Yes
Power-down
Yes
Note:ꢀ
1. For INT0, only level interrupt.
To enter any of the four sleep modes (Idle, ADC Noise Reduction, Power-down or Standby), the Sleep
Enable bit in the Sleep Mode Control Register (SMCR.SE) must be written to '1' and a SLEEP instruction
must be executed. Sleep Mode Select bits (SMCR.SM) select which sleep mode will be activated by the
SLEEP instruction.
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.
Note:ꢀ If a level triggered interrupt is used for wake-up the changed level must be held for some time to
wake up the MCU (and for the MCU to enter the interrupt service routine). See External Interrupts for
details.
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Related Links
SMCR on page 43
Interrupts on page 55
11.3.1. Idle Mode
When the SMCR.SM is written to '0x000', the SLEEP instruction makes the MCU enter Idle mode,
stopping the CPU but allowing the Analog Comparator, Timer/Counters, Watchdog, and the interrupt
system to continue operating. This sleep mode basically halts clkCPU and clkNVM, 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. 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.ACD). This will reduce power consumption in Idle mode. If the ADC is enabled , a conversion
starts automatically when this mode is entered.
Related Links
ACSRA on page 162
11.3.2. ADC Noise Reduction Mode
When the SMCR.SM is written to '0x001', the SLEEP instruction makes the MCU enter ADC Noise
Reduction mode, stopping the CPU but allowing the ADC, the external interrupts and the Watchdog to
continue operating (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkNVM, 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.
This mode is available in all devices equipped with an ADC.
11.3.3. Power-Down Mode
When the SMCR.SM is written to '0x010', the SLEEP instruction makes the MCU enter Power-Down
mode. In this mode, the external Oscillator is stopped, while the external interrupts and the Watchdog
continue operating (if enabled).
Only an these events can wake up the MCU:
•
•
•
Watchdog System Reset
External level interrupt on INT0
Pin change interrupt
This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.
11.3.4. Standby Mode
When the SMCR.SM is written to '0x100', 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. This reduces
wake-up time, because the oscillator is already running and doesn't need to be started up.
11.4. Power Reduction Register
The Power Reduction Register (PRR) provides a method to stop the clock to individual peripherals to
reduce power consumption. When the clock for a peripheral is stopped then:
•
The current state of the peripheral is frozen.
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•
•
The associated registers can not be read or written.
Resources used by the peripheral will remain occupied.
The peripheral should in most cases be disabled before stopping the clock. Clearing the PRR bit wakes
up the peripheral and puts it in the same state as before shutdown.
Peripheral module 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.
Related Links
PRR on page 44
Supply Current of I/O Modules on page 222
11.5. Minimizing Power Consumption
There are several possibilities 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.
11.5.1. Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. In the power-down
mode, the analog comparator is automatically disabled. See Analog Comparator for further details.
When entering ADC Noise Reduction mode, the Analog Comparator should be 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.
Related Links
AC - Analog Comparator on page 160
11.5.2. 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.
Related Links
ADC - Analog to Digital Converter on page 166
11.5.3. Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by 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.
11.5.4. 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.
Related Links
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Watchdog Timer on page 48
11.5.5. 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) is 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 Digital Input Enable and Sleep
Modes 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 0 (DIDR0).
Related Links
Digital Input Enable and Sleep Modes on page 69
DIDR0 on page 165
11.6. Register Description
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11.6.1. Sleep Mode Control Register
The Sleep Mode Control Register contains control bits for power management.
Name:ꢀ SMCR
Offset:ꢀ 0x3A
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
6
5
4
3
2
SM[2:0]
R/W
0
1
0
SE
R/W
0
Access
Reset
R/W
0
R/W
0
Bits 3:1 – SM[2:0]:ꢀSleep Mode Select
The SM[2:0] bits select between the five available sleep modes.
Table 11-2.ꢀSleep Mode Select
SM[2:0]
000
Sleep Mode
Idle
001
ADC Noise Reduction
Power-down
Reserved
010
011
100
Standby
101
Reserved
110
Reserved
111
Reserved
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.
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11.6.2. Power Reduction Register
Name:ꢀ PRR
Offset:ꢀ 0x35
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
PRUSART0
R/W
1
PRADC
R/W
0
0
PRTIM0
R/W
0
Access
Reset
0
Bit 2 – PRUSART0:ꢀPower Reduction USART0
Writing a logic one to this bit shuts down the USART by stopping the clock to the module. When waking
up the USART again, the USART should be re initialized to ensure proper operation.
Bit 1 – 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.
Bit 0 – 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.
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12.
SCRST - System Control and Reset
12.1. Overview
The reset logic manages the reset of the microcontroller. It issues a microcontroller reset, sets the device
to its initial state and allows the reset source to be identified by software.
12.2. Features
•
Reset The Microcontroller to Initial State.
•
Multiple Reset Sources:
–
–
–
–
Power-on Reset
VCC Level Monitoring (VLM) Reset
External Reset
Watchdog System Reset
12.3. 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 an Relative Jump instruction (RJMP) 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. The circuit diagram in the next shows
the reset logic. Electrical parameters of the reset circuitry are defined in section System and Reset
Characteristics.
Figure 12-1.ꢀReset Logic
DATA BUS
Reset Flag Register
VLM
(RSTFLR)
Power-on Reset
Circuit
Pull-up Resistor
SPIKE
FILTER
Watchdog
Oscillator
Delay Counters
Clock
CK
Generator
TIMEOUT
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.
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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.
Related Links
Starting from Reset on page 33
System and Reset Characteristics on page 214
12.4. Reset Sources
The device has four sources of reset:
•
•
•
•
Power-on Reset. The MCU is reset when the supply voltage is less than the Power-on Reset
threshold (VPOT).
VLM (VCC Level Monitoring) Reset. The MCU is reset when voltage on the VCC pin is below the
selected trigger level.
External Reset. The MCU is reset when a low level is present on the RESET pin for longer than the
minimum pulse length.
Watchdog System Reset. The MCU is reset when the Watchdog Timer period expires and the
Watchdog System Reset mode is enabled.
12.4.1. Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. 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 12-2.ꢀMCU Start-up, RESET Tied to VCC
VPOT
VCC
VRST
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
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Figure 12-3.ꢀMCU Start-up, RESET Extended Externally
VPOT
VCC
VRST
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
Related Links
System and Reset Characteristics on page 214
12.4.2. VCC Level Monitoring
ATtiny102/ATtiny104 have a VCC Level Monitoring (VLM) circuit that compares the voltage level at the
VCC pin against fixed trigger levels. The trigger levels are set with VLM[2:0] bits, see VLMCSR – VCC
Level Monitoring Control and Status register.
The VLM circuit provides a status flag, VLMF, that indicates if voltage on the VCC pin is below the
selected trigger level. The flag can be read from VLMCSR, but it is also possible to have an interrupt
generated when the VLMF status flag is set. This interrupt is enabled by the VLMIE bit in the VLMCSR
register. The flag can be cleared by changing the trigger level or by writing it to zero. The flag is
automatically cleared when the voltage at VCC rises back above the selected trigger level.
The VLM can also be used to improve reset characteristics at falling supply. Without VLM, the Power-On
Reset (POR) does not activate before supply voltage has dropped to a level where the MCU is not
necessarily functional any more. With VLM, it is possible to generate a reset earlier.
When active, the VLM circuit consumes some power, as illustrated in the figure of VCC Level Monitor
Current vs. VCC in Typical Characteristics. To save power the VLM circuit can be turned off completely, or
it can be switched on and off at regular intervals. However, detection takes some time and it is therefore
recommended to leave the circuitry on long enough for signals to settle. See VCC Level Monitor.
When VLM is active and voltage at VCC is above the selected trigger level operation will be as normal and
the VLM can be shut down for a short period of time. If voltage at VCC drops below the selected threshold
the VLM will either flag an interrupt or generate a reset, depending on the configuration.
When the VLM has been configured to generate a reset at low supply voltage it will keep the device in
reset as long as VCC is below the reset level. If supply voltage rises above the reset level the condition is
removed and the MCU will come out of reset, and initiate the power-up start-up sequence.
If supply voltage drops enough to trigger the POR then PORF is set after supply voltage has been
restored.
Related Links
VLMCSR on page 53
Electrical Characteristics on page 210
VCC Level Monitor on page 215
Typical Characteristics on page 218
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12.4.3. External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the minimum
pulse width 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. The External Reset
can be disabled by the RSTDISBL fuse.
Figure 12-4.ꢀExternal Reset During Operation
CC
Related Links
System and Reset Characteristics on page 214
12.4.4. Watchdog System 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
.
Figure 12-5.ꢀWatchdog System Reset During Operation
CC
CK
12.5. 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 Watchdog System Reset for details on how to configure the watchdog timer.
12.5.1. Overview
The Watchdog Timer is clocked from an on-chip oscillator, which runs at 128kHz, as the next figure. By
controlling the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted. The Watchdog
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Reset (WDR) instruction resets the Watchdog Timer. The Watchdog Timer is also reset when it is
disabled and when a device reset occurs. Ten different clock cycle periods can be selected to determine
the reset period. If the reset period expires without another Watchdog Reset, the device resets and
executes from the Reset Vector.
Figure 12-6.ꢀWatchdog Timer
WATCHDOG
PRESCALER
128 kHz
OSCILLATOR
WATCHDOG
RESET
WDP0
WDP1
WDP2
WDP3
MUX
WDE
MCU RESET
The Watchdog Timer can also be configured to generate an interrupt instead of a reset. This can be very
helpful when using the Watchdog to wake-up from Power-down.
To prevent unintentional disabling of the Watchdog or unintentional change of time-out period, two
different safety levels are selected by the fuse WDTON. See Procedure for Changing the Watchdog Timer
Configuration for details.
Table 12-1.ꢀWDT Configuration as a Function of the Fuse Settings of WDTON
WDTON
Safety Level WDT Initial
State
How to Disable the
WDT
How to Change Time-
out
Unprogrammed 1
Disabled
Protected change
sequence
No limitations
Programmed
2
Enabled
Always enabled
Protected change
sequence
12.5.2. Procedure for Changing the Watchdog Timer Configuration
The sequence for changing configuration differs between the two safety levels, as follows:
12.5.2.1. Safety Level 1
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit to one
without any restriction. A special sequence is needed when disabling an enabled Watchdog Timer. To
disable an enabled Watchdog Timer, the following procedure must be followed:
1. Write the signature for change enable of protected I/O registers to register CCP
2. Within four instruction cycles, in the same operation, write WDE and WDP bits
12.5.2.2. Safety Level 2
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A
protected change is needed when changing the Watchdog Time-out period. To change the Watchdog
Time-out, the following procedure must be followed:
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1. Write the signature for change enable of protected I/O registers to register CCP
2. Within four instruction cycles, write the WDP bit. The value written to WDE is irrelevant
12.5.3. Code Examples
The following code example shows how to turn off the WDT. The example assumes that interrupts are
controlled (e.g., by disabling interrupts globally) so that no interrupts will occur during execution of these
functions.
Assembly Code Example
WDT_off:
wdr
; Clear WDRF in RSTFLR
in r16, RSTFLR
andi r16, ~(1<<WDRF)
out RSTFLR, r16
; Write signature for change enable of protected I/O register
ldi r16, 0xD8
out CCP, r16
; Within four instruction cycles, turn off WDT
ldi r16, (0<<WDE)
out WDTCSR, r16
ret
Note:ꢀ See About Code Examples.
12.6. Register Description
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12.6.1. Watchdog Timer Control Register
Name:ꢀ WDTCSR
Offset:ꢀ 0x31
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
WDIF
R/W
0
6
WDIE
R/W
0
5
WDP3
R/W
0
4
3
WDE
R/W
x
2
WDP2
R/W
0
1
WDP1
R/W
0
0
WDP0
R/W
0
Access
Reset
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.
Table 12-2.ꢀWatchdog Timer Configuration
WDTON(1) WDE WDIE Mode
Action on Time-out
None
1
1
1
1
0
0
0
1
1
X
0
1
0
1
X
Stopped
Interrupt Mode
System Reset Mode
Interrupt
Reset
Interrupt and System Reset Mode Interrupt, then go to System Reset Mode
System Reset Mode Reset
Note:ꢀ
1. WDTON Fuse set to “0” means programmed and “1” means unprogrammed.
Bit 3 – WDE:ꢀWatchdog System Reset Enable
WDE is overridden by WDRF in RSTFLR. 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.
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Bits 5,2:0 – WDPn:ꢀWatchdog Timer Prescaler [n=3:0]
The WDP[3:0] 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 the table below.
Table 12-3.ꢀWatchdog Timer Prescale Select
WDP[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
Number of WDT Oscillator Cycles
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
Reserved
Typical Time-out at VCC = 5.0V
16ms
32ms
64ms
0.125s
0.25s
0.5s
1.0s
2.0s
1000
1001
1010
1011
1100
1101
1110
4.0s
8.0s
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
1111
Reserved
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12.6.2. VCC Level Monitoring Control and Status register
Name:ꢀ VLMCSR
Offset:ꢀ 0x34
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
VLMF
R
6
VLMIE
R/W
0
5
4
3
2
1
VLM[2:0]
R/W
0
Access
Reset
R/W
0
R/W
0
0
0
Bit 7 – VLMF:ꢀVLM Flag
This bit is set by the VLM circuit to indicate that a voltage level condition has been triggered. The bit is
cleared when the trigger level selection is set to “Disabled”, or when voltage at VCC rises above the
selected trigger level.
Bit 6 – VLMIE:ꢀVLM Interrupt Enable
When this bit is set the VLM interrupt is enabled. A VLM interrupt is generated every time the VLMF flag
is set.
Bits 2:0 – VLM[2:0]:ꢀTrigger Level of Voltage Level Monitor
These bits set the trigger level for the voltage level monitor.
Table 12-4.ꢀSetting the Trigger Level of Voltage Level Monitor
VLM[2:0] Label
Description
000
001
010
VLM0
VLM1L
VLM1H
Voltage Level Monitor disabled
Triggering generates a regular Power-On Reset (POR).
The VLM flag is not set
011
100
101
110
111
VLM2
VLM3
Triggering sets the VLM Flag (VLMF) and generates a VLM interrupt, if enabled
Not allowed
Not allowed
Not allowed
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12.6.3. Reset Flag Register
Name:ꢀ RSTFLR
Offset:ꢀ 0x3B
Reset:ꢀ N/A
Property: -
ꢀ
Bit
7
6
5
4
3
WDRF
R/W
x
2
1
EXTRF
R/W
x
0
PORF
R/W
x
Access
Reset
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 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.
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13.
Interrupts
13.1. Overview
This section describes the specifics of the interrupt handling of the device. For a general explanation of
the AVR interrupt handling, refer to the description of Reset and Interrupt Handling.
Related Links
Reset and Interrupt Handling on page 21
13.2. Interrupt Vectors
Interrupt vectors are described in the table below.
Table 13-1.ꢀReset and Interrupt Vectors
Vector No. Program Address Source
Interrupt Definition
1
0x000
RESET
External Pin, Power-on Reset, VLM Reset and
Watchdog Reset
2
0x001
0x002
0x003
0x004
0x005
0x006
0x007
0x008
0x009
0x00A
0x00B
0x00C
0x00D
0x00E
0x00F
INT0
External Interrupt Request 0
Pin Change Interrupt Request 0
Pin Change Interrupt Request 1
Timer/Counter0 Capture
3
PCINT0
4
PCINT1
5
TIM0_CAPT
TIM0_OVF
6
Timer/Counter0 Overflow
7
TIM0_COMPA Timer/Counter0 Compare Match A
TIM0_COMPB Timer/Counter0 Compare Match B
8
9
ANA_COMP
WDT
Analog Comparator
10
11
12
13
14
15
16
Watchdog Time-out Interrupt
VCC Voltage Level Monitor
ADC Conversion Complete
VLM
ADC
USART0_RXS USART0 Rx Start
USART0_RXC USART0 Rx Complete
USART0_DRE USART0 Data Register Empty
USART0_TXC USART0 Tx Complete
In case the program never enables an interrupt source, the Interrupt Vectors will not be used and,
consequently, regular program code can be placed at these locations.
The most typical and general program setup for the Reset and Interrupt Vector Addresses in this device
is:
Address Labels
0x000
0x001
Code
rjmp RESET
rjmp INT0
Comments
; Reset Handler
; IRQ0 Handler
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0x002
0x003
0x004
0x005
0x006
0x007
0x008
0x009
0x00A
0x00B
0x00C
0x00D
0x00E
0x00F
rjmp PCINT0
; PCINT0 Handler
rjmp PCINT1
; PCINT1 Handler
rjmp TIM0_CAPT
rjmp TIM0_OVF
rjmp TIM0_COMPA
rjmp TIM0_COMPB
rjmp ANA_COMP
rjmp WDT
rjmp VLM
rjmp ADC
rjmp USART0_RXS
rjmp USART0_RXC
rjmp USART0_DRE
rjmp USART0_TXC
; Timer/Counter0 Capture Handler
; Timer/Counter0 Overflow Handler
; Timer/Counter0 Compare Match A Handler
; Timer/Counter0 Compare Match B Handler
; Analog Comparator Handler
; Watchdog Timer Handler
; Voltage Level Monitor Handler
; ADC Conversion Handler
; USART0 Rx Start Handler
; USART0 Rx Complete Handler
; USART0 Data Register Empty Handler
; USART0 Tx Complete Handler
0x010
0x011
0x012
0x013
0x014
0x015
...
RESET:
ldi r16, high (RAMEND) ; Main program start
out SPH, r16
ldi r16, low(RAMEND)
out SPL, r16
sei
; Set Stack Pointer
; to top of RAM
; Enable interrupts
<instr>
...
13.3. External Interrupts
The External Interrupts are triggered by the INT0 pins or any of the PCINT[11:0] pins. Observe that, if
enabled, the interrupts will trigger even if the INT0 or PCINT[11:0] pins are configured as outputs. This
feature provides a way of generating a software interrupt. The pin change interrupt PCI0 will trigger if any
enabled PCINT[11:0] pin toggles. The Pin Change Mask 0/1 Register (PCMSK 0/1) controls which pins
contribute to the pin change interrupts. Pin change interrupts on PCINT[11:0] are detected
asynchronously. This implies that these interrupts can be used for waking the part also from sleep modes
other than Idle mode.
The INT0 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 Register A (EICRA). When the INT0 interrupts are
enabled and are configured as level triggered, the interrupts will trigger as long as the pin is held low.
Note that recognition of falling or rising edge interrupts on INT0 requires the presence of an I/O clock,
described in Clock Systems and their Distribution chapter.
Related Links
Clock System on page 30
EICRA on page 58
PCMSK0 on page 63
PCMSK1 on page 64
13.3.1. Low Level Interrupt
A low level interrupt on INT0 is detected asynchronously. This means that the interrupt source can be
used for waking the part also from sleep modes other than Idle (the I/O clock is halted in all sleep modes
except Idle).
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 as described in Clock System
If the low level on the interrupt pin is removed before the device has woken up then program execution
will not be diverted to the interrupt service routine but continue from the instruction following the SLEEP
command.
Related Links
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Clock System on page 30
13.3.2. Pin Change Interrupt Timing
An example of timing of a pin change interrupt is shown in the following figure.
Figure 13-1.ꢀTiming of pin change interrupts
pin_lat
pcint_in_(0)
PCINT(0)
clk
0
x
D
Q
pcint_syn
pcint_setflag
PCIF
pin_sync
PCINT(0) in PCMSK(x)
LE
clk
clk
PCINT(0)
pin_lat
pin_sync
pcint_in_(0)
pcint_syn
pcint_setflag
PCIF
13.4. Register Description
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13.4.1. External Interrupt Control Register A
The External Interrupt Control Register A contains control bits for interrupt sense control.
Name:ꢀ EICRA
Offset:ꢀ 0x15
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
ISC0[1:0]
Access
Reset
R/W
0
R/W
0
Bits 1:0 – ISC0[1:0]:ꢀInterrupt Sense Control 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corresponding
interrupt mask are set. The level and edges on the external INT0 pin that activate the interrupt are defined
in table below. The value on the INT0 pin is sampled before detecting edges. If edge or toggle interrupt is
selected, pulses that last longer than one clock period 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.
Value
00
01
10
11
Description
The low level of INT0 generates an interrupt request.
Any logical change on INT0 generates an interrupt request.
The falling edge of INT0 generates an interrupt request.
The rising edge of INT0 generates an interrupt request.
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13.4.2. External Interrupt Mask Register
Name:ꢀ EIMSK
Offset:ꢀ 0x13
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
INT0
R/W
0
Access
Reset
Bit 0 – INT0:ꢀExternal Interrupt Request 0 Enable
When the INT0 bit is set ('1') and the I-bit in the Status Register (SREG) is set ('1'), the external pin
interrupt is enabled. The Interrupt Sense Control 0 bits in the External Interrupt Control Register A
(EICRA.ISC0) define whether the external interrupt is activated on rising and/or falling edge of the INT0
pin or level sensed. Activity on the pin will cause an interrupt request even if INT0 is configured as an
output. The corresponding interrupt of External Interrupt Request 0 is executed from the INT0 Interrupt
Vector.
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13.4.3. External Interrupt Flag Register
Name:ꢀ EIFR
Offset:ꢀ 0x14
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
INTF0
R/W
0
Access
Reset
Bit 0 – INTF0:ꢀExternal Interrupt Flag 0
When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set (one). If
the I-bit in SREG and the INT0 bit in EIMSK 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. This flag is always cleared when INT0 is configured as a level
interrupt.
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13.4.4. Pin Change Interrupt Control Register
Name:ꢀ PCICR
Offset:ꢀ 0x12
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
PCIE1
R/W
0
0
PCIE0
R/W
0
Access
Reset
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 PCINT[11:8] pin will cause an interrupt. The
corresponding interrupt of Pin Change Interrupt Request is executed from the PCI1 Interrupt Vector.
PCINT[11:8] 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 PCINT[7:0] pin will cause an interrupt. The
corresponding interrupt of Pin Change Interrupt Request is executed from the PCI0 Interrupt Vector.
PCINT[7:0] pins are enabled individually by the PCMSK Register.
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13.4.5. Pin Change Interrupt Flag Register
Name:ꢀ PCIFR
Offset:ꢀ 0x11
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
PCIF1
R/W
0
0
PCIF0
R/W
0
Access
Reset
Bit 1 – PCIF1:ꢀPin Change Interrupt Flag 1
When a logic change on any PCINT[11:8] 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 PCINT[7:0] 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.
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13.4.6. Pin Change Mask Register 0
Name:ꢀ PCMSK0
Offset:ꢀ 0x0F
Reset:ꢀ 0x00
Property: -
ꢀ
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
PCINT0
R/W
0
Access
Reset
Bits 7:0 – PCINTn:ꢀPin Change Enable Mask [n = 7:0]
Each PCINT[7:0] bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If
PCINT[7:0] is set and the PCIE0 bit in PCICR is set, pin change interrupt is enabled on the corresponding
I/O pin. If PCINT[7:0] is cleared, pin change interrupt on the corresponding I/O pin is disabled.
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13.4.7. Pin Change Mask Register 1
Name:ꢀ PCMSK1
Offset:ꢀ 0x10
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
PCINT11
R/W
2
PCINT10
R/W
1
PCINT9
R/W
0
0
PCINT8
R/W
0
Access
Reset
0
0
Bits 0, 1, 2, 3 – PCINT8, PCINT9, PCINT10, PCINT11:ꢀPin Change Enable Mask [11:8]
Each PCINT[11:8]-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If
PCINT[11:8] is set and the PCICR.PCIE1 is set, pin change interrupt is enabled on the corresponding I/O
pin. If PCINT[11:8] 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.
14.2. Features
•
All AVR Ports Have True Read-Modify-Write Functionality.
•
•
Flexible Pin configuration Through the Dedicated Registers.
Each Output Buffer Has Symmetrical Drive Characteristics with both High Sink and Source
Capability.
14.3. I/O Pin Equivalent Schematic
All I/O pins have protection diodes to both VCC and Ground as indicated in the following figure.
Figure 14-1.ꢀI/O Pin Equivalent Schematic
Rpu
Pxn
Logic
Cpin
See Figure
"General Digital I/O" fo
Details
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.
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 '1' 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 next section. 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 Alternate Port Functions section in this chapter. Refer to the individual module
sections for a full description of the alternate functions.
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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.
Related Links
Electrical Characteristics on page 210
14.4. Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. The following figure shows a
functional description of one I/O-port pin, here generically called Pxn.
Figure 14-2.ꢀGeneral Digital I/O
REx
Q
D
PUExn
Q CLR
RESET
WEx
Q
D
DDxn
Q CLR
WDx
RDx
RESET
1
0
Q
D
Pxn
PORTxn
Q CLR
RESET
WPx
WRx
SLEEP
RRx
SYNCHRONIZER
RPx
D
Q
D
L
Q
Q
PINxn
Q
clk I/O
REx:
READPUEx
WDx:
RDx:
WRx:
RRx:
RPx:
WPx:
WRITEDDRx
READDDRx
WRITEPORTx
READPORTx REGISTER
READPORTx PIN
WRITEPINx REGISTER
SLEEP: SLEEP CONTROL
clkI/O: I/O CLOCK
Note:ꢀ WEx, WRx, WPx, WDx, REx, RRx, RPx, and RDx are common to all pins within the same port.
clkI/O, SLEEP are common to all ports.
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14.4.1. Configuring the Pin
Each port pin consists of four register bits: DDxn, PORTxn, PUExn, and PINxn. As shown in the Register
Description in this chapter, 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 to '1', Pxn is
configured as an output pin. If DDxn is written to '0', Pxn is configured as an input pin.
If PORTxn is written to '1' 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 to '0' 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.
Table 14-1.ꢀPort Pin Configurations
DDxn PORTxn PUExn I/O
Pull-up Comment
0
0
1
1
x
x
0
0
0
1
0
1
Input No
Tri-state (hi-Z)
Input Yes
Output No
Output Yes
Sources current if pulled low externally
Output low (sink)
NOT RECOMMENDED.
Output low (sink) and internal pull-up active. Sources
current through the internal pull-up resistor and consumes
power constantly
1
1
1
1
0
1
Output No
Output Yes
Output high (source)
Output high (source) and internal pull-up active
Port pins are tri-stated when a reset condition becomes active, even when no clocks are running.
14.4.2. Toggling the Pin
Writing a '1' to PINxn toggles the value of PORTxn, independent on the value of DDRxn. The SBI
instruction can be used to toggle one single bit in a port.
14.4.3. Break-Before-Make Switching
In Break-Before-Make mode, switching the DDRxn bit from input to output introduces an immediate tri-
state period lasting one system clock cycle, as indicated in the figure below. For example, if the system
clock is 4 MHz and the DDRxn is written to make an output, an immediate tri-state period of 250 ns is
introduced before the value of PORTxn is seen on the port pin.
To avoid glitches it is recommended that the maximum DDRxn toggle frequency is two system clock
cycles. The Break-Before-Make mode applies to the entire port and it is activated by the BBMx bit. For
more details, see PORTCR – Port Control Register.
When switching the DDRxn bit from output to input no immediate tri-state period is introduced.
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Figure 14-3.ꢀSwitching Between Input and Output in Break-Before-Make-Mode
SYSTEM CLK
0x02
r16
0x01
r17
out DDRx, r16
nop
out DDRx, r17
INSTRUCTIONS
PORTx
0x55
0x02
0x01
0x01
DDRx
tri-state
Px0
Px1
tri-state
tri-state
intermediate tri-state cycle
intermediate tri-state cycle
Related Links
PORTCR on page 88
14.4.4. 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, 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. The following figure 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.
Figure 14-4.ꢀSynchronization when Reading an Externally Applied Pin value
SYSTEM CLK
XXX
XXX
in r17, PINx
INSTRUCTIONS
SYNC LATCH
PINxn
0x00
tpd, max
0xFF
r17
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 the
following figure. 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.
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Figure 14-5.ꢀSynchronization when Reading a Software Assigned Pin Value
SYSTEM CLK
0xFF
r16
out PORTx, r16
nop
in r17, PINx
INSTRUCTIONS
SYNC LATCH
PINxn
0x00
tpd
0xFF
r17
14.4.5. Digital Input Enable and Sleep Modes
As shown in the figure of General Digital I/O, 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 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 Alternate Port Functions section in this chapter.
If a logic high level 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.
14.4.6. 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.
14.4.7. Program Example
The following code example shows how to set port B pin 0 high, pin 1 low, and define the port pins from 2
to 3 as input with a pull-up assigned to port pin 2. 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.
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Assembly Code Example
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi r16,(1<<PUEB2)
ldi r17,(1<<PB0)
ldi r18,(1<<DDB1)|(1<<DDB0)
out PUEB,r16
out PORTB,r17
out DDRB,r18
; Insert nop for synchronization
nop
; Read port pins
in r16,PINB
...
14.4.8. Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. The following figure
shows how the port pin control signals from the simplified in the figure of Ports as General Digital I/O 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.
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Figure 14-6.ꢀAlternate Port Functions
PUOExn
PUOVxn
REx
1
0
Q
D
PUExn
Q CLR
DDOExn
DDOVxn
RESET
WEx
1
0
Q
D
DDxn
Q CLR
WDx
RDx
PVOExn
PVOVxn
RESET
1
1
0
Pxn
Q
D
0
PORTxn
PTOExn
Q CLR
DIEOExn
DIEOVxn
SLEEP
WPx
RESET
WRx
1
0
RRx
SYNCHRONIZER
RPx
SET
D
Q
D
L
Q
Q
PINxn
Q
CLR
CLR
clk I/O
DIxn
AIOxn
WEx:
REx:
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
WRITEPUEx
READPUEx
WRITEDDRx
READDDRx
READPORTx REGISTER
WRITEPORTx
PUOExn:
PUOVxn:
DDOExn:
Pxn PULL-UPOVERRIDEENABLE
Pxn PULL-UPOVERRIDEVALUE
Pxn DATADIRECTIONOVERRIDEENABLE
DDOVxn: Pxn DATADIRECTIONOVERRIDEVALUE
PVOExn:
PVOVxn:
Pxn PORTVALUEOVERRIDEENABLE
Pxn PORTVALUEOVERRIDEVALUE
READPORTx PIN
WRITEPINx
DIEOExn: Pxn DIGITALINPUT-ENABLEOVERRIDEENABLE
DIEOVxn: Pxn DIGITALINPUT-ENABLEOVERRIDEVALUE
clkI/O
:
I/OCLOCK
SLEEP:
PTOExn:
SLEEPCONTROL
Pxn,PORTTOGGLEOVERRIDEENABLE
DIxn:
AIOxn:
DIGITALINPUTPINn ONPORTx
ANALOGINPUT/OUTPUTPINn ONPORTx
Note:ꢀ 1. WEx, WRx, WPx, WDx, REx, RRx, RPx, and RDx are common to all pins within the same port.
clkI/O and SLEEP are common to all ports. All other signals are unique for each pin.
The following table summarizes the function of the overriding signals. The pin and port indexes from
previous figure are not shown in the succeeding tables. The overriding signals are generated internally in
the modules having the alternate function.
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Table 14-2.ꢀGeneric Description of Overriding Signals for Alternate Functions
Signal Name Full Name
Description
PUOE
PUOV
DDOE
Pull-up Override
Enable
If this signal is set, the pull-up enable is controlled by the PUOV signal.
If this signal is cleared, the pull-up is enabled when PUExn = 0b1.
Pull-up Override Value If PUOE is set, the pull-up is enabled/disabled when PUOV is set/
cleared, regardless of the setting of the PUExn Register bit.
Data Direction
Override Enable
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.
DDOV
PVOE
Data Direction
Override Value
If DDOE is set, the Output Driver is enabled/disabled when DDOV is
set/cleared, regardless of the setting of the DDxn Register bit.
Port Value Override
Enable
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.
PVOV
PTOE
DIEOE
Port Value Override
Value
If PVOE is set, the port value is set to PVOV, regardless of the setting of
the PORTxn Register bit.
Port Toggle Override
Enable
If PTOE is set, the PORTxn Register bit is inverted.
Digital Input Enable
Override Enable
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).
DIEOV
DI
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).
Digital Input
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.
AIO
Analog Input/Output
This is the Analog Input/output to/from alternate functions. The signal is
connected directly to the pad, and can be used bi-directionally.
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.
14.4.8.1. Alternate Functions of Port A
The Port A pins with alternate functions are shown in the table below:
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Table 14-3.ꢀPort A Pins Alternate Functions
Port Pin
Alternate Functions
PA[0]
ADC0: ADC Input Channel 0
AIN0: Analog Comparator, Positive Input
T0: Timer/Counter0 Clock Source (default location)
PCINT0: Pin Change Interrupt source 0
CLKI: External Clock
TPICLK: Serial Programming Clock
PA[1]
ADC1: ADC Input Channel 1
AIN1: Analog Comparator, Negative Input
OC0B: Timer/Counter0 Compare Match B Output (default
location)
PCINT1: Pin Change Interrupt source 1
TPIDATA: Serial Programming Data
PA[2]
PA[3]
PCINT2: Pin Change Interrupt source 2
RESET: Reset Pin
OC0A: Timer/Counter0 Compare Match A Output (alternative
location)
PCINT3: Pin Change Interrupt source 3
PA[4]
PA[5]
ICP0: Timer/Counter0 Input Capture Input (alternative
location)
PCINT4: Pin Change Interrupt source 4
ADC2: ADC Input Channel 2
OC0B: Timer/Counter0 Compare Match B Output (alternative
location)
PCINT5: Pin Change Interrupt source 5
PA[6]
PA[7]
ADC3: ADC Input Channel 3
PCINT6: Pin Change Interrupt source 6
PCINT7: Pin Change Interrupt source 7
The alternate pin configuration is as follows:
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•
PA[0] – ADC0/AIN0/T0/PCINT0/CLKI/TPICLK
–
–
ADC0: Analog to Digital Converter, Channel 0.
AIN0: Analog Comparator Positive Input. Configure the port pin as input with the internal pull-
up switched off to avoid the digital port function from interfering with the function of the Analog
Comparator.
–
–
T0: Timer/Counter0 counter source.
PCINT0: Pin Change Interrupt source 0. The PA[0] pin can serve as an external interrupt
source for pin change interrupt 0.
–
–
CLKI: External Clock.
TPICLK: Serial Programming Clock.
•
PA[1] – ADC1/AIN1/OC0B/PCINT1/TPIDATA
–
–
ADC1: Analog to Digital Converter, Channel 1.
AIN1: Analog Comparator Negative Input. Configure the port pin as input with the internal
pull-up switched off to avoid the digital port function from interfering with the function of the
Analog Comparator.
–
OC0B: Output Compare Match B Output. The PA[1] pin can serve as an external output for
the Timer/Counter0 Compare Match B. The PA[1] pin has to be configured as an output
(DDB1 set (one)) to serve this function. The OC0B pin is also the output pin for the PWM
mode timer function.
–
–
PCINT1: Pin Change Interrupt source 1. The PA[1] pin can serve as an external interrupt
source for pin change interrupt 0.
TPIDATA: Serial Programming Data.
•
•
PA[2] – PCINT2/RESET
–
PCINT2: Pin Change Interrupt source 2. The PA[2] pin can serve as an external interrupt
source for pin change interrupt 0.
–
RESET: Reset Pin.
PA[3] – OC0A/PCINT3
–
OC0A: Output Compare Match A Output. The PA[3] pin can serve as an external output for
the Timer/Counter0 Compare Match A. The pin has to be configured as an output (DDB0 set
(one)) to serve this function. This is also the output pin for the PWM mode timer function.
–
PCINT3: Pin Change Interrupt source 3. The PA[3] pin can serve as an external interrupt
source for pin change interrupt 0.
•
•
PA[4] - ICP0/PCINT4
–
–
ICP0: Input Capture Pin. The PA[4] pin can act as an Input Capture pin for Timer/Counter0.
PCINT4: Pin Change Interrupt source 4. The PA4 pin can serve as an external interrupt
source for pin change interrupt 0.
PA[5] - ADC2/OC0B/PCINT5
–
–
ADC2: Analog to Digital Converter, Channel 2.
OC0B: Output Compare Match B Output: The PA1 pin can serve as an external output for the
Timer/Counter0 Compare Match B. The PA[5] pin has to be configured as an output (DDB1
set (one)) to serve this function. The OC0B pin is also the output pin for the PWM mode timer
function.
–
PCINT5: Pin Change Interrupt source 5. The PA5 pin can serve as an external interrupt
source for pin change interrupt 0.
•
PA[6] - ADC3/PCINT6
ADC3: Analog to Digital Converter, Channel 3.
–
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–
PCINT6: Pin Change Interrupt source 6. The PA6 pin can serve as an external interrupt
source for pin change interrupt 0.
•
PA[7] - PCINT7
PCINT7: Pin Change Interrupt source 7. The PA7 pin can serve as an external interrupt
source for pin change interrupt 0.
–
The following tables relate the alternate functions of Port B to the overriding signals shown in the figure of
Alternate Port Functions.
Table 14-4.ꢀOverriding Signals for Alternate Functions in PA[7:6]
Signal
Name
PA7/PCINT7
PA6/ADC3/PCINT6
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
PTOE
DIEOE
DIEOV
DI
0
0
0
0
0
0
0
0
0
0
0
0
0
0
(PCINT7 • PCIE0)
PCINT7 • PCIE0
PCINT7 Input
-
(PCINT6 • PCIE0) + ADC3D
PCINT6 • PCIE0
PCINT6 input
AIO
ADC3
Table 14-5.ꢀOverriding Signals for Alternate Functions in PA[5:4]
Signal
Name
PA5/ADC2/OC0B/PCINT5
PA4/ICP0/PCINT4
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
PTOE
DIEOE
DIEOV
DI
0
0
0
0
0
0
0
0
(OC0B Enable • REMAP)
(OC0B • REMAP)
0
0
0
0
(PCINT5 • PCIE0) + ADC2D
PCINT5 • PCIE0
PCINT5 Input
(PCINT4 • PCIE0)
(PCINT4 • PCIE0)
ICP0/PCINT4 Input
-
AIO
ADC2
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Table 14-6.ꢀOverriding Signals for Alternate Functions in PA[3:2]
Signal
Name
PA3/OC0A/PCINT3
PA4/ICP0/PCINT4
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
PTOE
DIEOE
DIEOV
DI
0
RSTDISBL(1)
0
1
0
RSTDISBL(1)
0
0
(OC0A Enable • REMAP)
(OC0A • REMAP)
0
0
0
0
(PCINT3 • PCIE0)
PCINT3 • PCIE0
PCINT3 Input
-
RSTDISBL(1) + (PCINT2 • PCIE0)
RSTDISBL • PCINT2 • PCIE0
PCINT2 input
-
AIO
Note:ꢀ
1. RSTDISBL is 1 when the configuration bit is “0” (Programmed).
Table 14-7.ꢀOverriding Signals for Alternate Functions in PA[1:0]
Signal PA1/ADC1/AIN1/OC0B/PCINT1
Name
PA0/ADC0/AIN0/CLKI/T0/PCINT0
PUOE
PUOV
DDOE
DDOV
0
0
0
0
EXT_CLOCK(1)
0
EXT_CLOCK(1)
0
PVOE (OC0B Enable • REMAP)
PVOV (OC0B • REMAP)
EXT_CLOCK(1)
0
PTOE
0
0
DIEOE (PCINT1 • PCIE0) + ADC1D
DIEOV PCINT1 • PCIE0
EXT_CLOCK(1) + (PCINT0 • PCIE0) + ADC0D
EXT_CLOCK(1)• PWR_DOWN) + (EXT_CLOCK(1)• PCINT0 •
PCIE0)
DI
PCINT1 Input
CLKI/T0/PCINT0 Input
AIO
ADC1/Analog Comparator Negative Input ADC0/Analog Comparator Positive Input
Note:ꢀ
1. EXT_CLOCK is 1 when external clock is selected as main clock.
14.4.8.2. Alternate Functions of Port B
The Port B pins with alternate functions are shown in the table below:
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Table 14-8.ꢀPort B Pins Alternate Functions
Port Pin
Alternate Functions
PB[0]
ADC4: ADC Input Channel 4
PCINT8: Pin Change Interrupt source 8
PB[1]
ADC5: ADC Input Channel 5
OC0A: Timer/Counter0 Compare Match A Output (default
location)
PCINT9: Pin Change Interrupt source 9
INT0: External Interrupt 0 Source
CLKO: System Clock Output
PB[2]
ADC6: ADC Input Channel 6
ICP0: Timer/Counter0 Input Capture Input (default
location)
TxD0: USART Output
PCINT10: Pin Change Interrupt source 10
PB[3]
ACO: AC Output
ADC7: ADC Input Channel 7
T0: Timer/Counter0 Clock Source (alternative location)
RxD0: USART Input
PCINT11: Pin Change Interrupt source 11
The alternate pin configuration is as follows:
•
PB[0] – ADC4/PCINT8
–
–
ADC4: Analog to Digital Converter, Channel 4.
PCINT8: Pin Change Interrupt source 8. The PB[0] pin can serve as an external interrupt
source for pin change interrupt 1.
•
PB[1] – ADC5/OC0A/PCINT9/INT0/CLKO
–
–
ADC5: Analog to Digital Converter, Channel 5
OC0A: Output Compare Match output. The PB[1] pin can serve as an external output for the
Timer/Counter0 Compare Match A. The PB[1] pin has to be configured as an output (DDB0
set (one)) to serve this function. The OC0A pin is also the output pin for the PWM mode timer
function.
–
–
PCINT9: Pin Change Interrupt source 9. The PB[1] pin can serve as an external interrupt
source for pin change interrupt 1.
INT0: External Interrupt Request 0.
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–
CLKO: System Clock Output. The system clock can be output on pin PB[1]. The system clock
will be output if CKOUT bit is programmed, regardless of the PORTB2 and DDB2 settings.
•
•
PB[2] – ADC6/ICP0/TxD0/PCINT10
–
–
–
ADC6: Analog to Digital Converter, Channel 6.
ICP0: Input Capture Pin. The PB[2] pin can act as an Input Capture pin for Timer/Counter0.
PCINT10: Pin Change Interrupt source 10. The PB[2] pin can serve as an external interrupt
source for pin change interrupt 1.
–
TxD0: USART Output
PB[3] – ACO/ADC7/T0/RXD0/PCINT3/RXD0
–
–
–
–
ACO: AC Output
ADC7: Analog to Digital Converter, Channel 7.
T0: Timer/Counter0 counter source.
PCINT11: Pin Change Interrupt source 11. The PB[3] pin can serve as an external interrupt
source for pin change interrupt 1.
–
RXD0: USART input
The following tables relate the alternate functions of Port B to the overriding signals shown in the figure of
Alternate Port Functions.
Table 14-9.ꢀOverriding Signals for Alternate Functions in PB[3:2]
Signal
Name
PB3/ADC7/ACO/RxD0/T0/PCINT11
PB2/ADC6/TxD0/ICP0/PCINT10
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
PTOE
DIEOE
DIEOV
DI
ACOE
TxEN0
0
0
RxEN0 + (RxEN0 • ACOE)
ACOE
TxEN0
TxEN0
ACOE
TxEN0
ACO • ACOE
TxEN0• TXD0_OUT
0
0
(PCINT11 • PCIE1) + ADC7D
PCINT11• PCIE1
RxD0/T0/PCINT11 Input
ADC7/ AC Output
(PCINT10 • PCIE1) + ADC6D
PCINT10 • PCIE1
ICP0/PCINT10 input
ADC6
AIO
Table 14-10.ꢀOverriding Signals for Alternate Functions in PB[1:0]
Signal PB1/ADC5/INT0/XCK0/CLKO/OC0A/PCINT9
Name
PB0/ADC4/PCINT8
PUOE CKOUT(1)
0
0
0
PUOV
0
DDOE CKOUT(1)+ (OC0A Enable • REMAP) + XCK0_MASTER
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Signal PB1/ADC5/INT0/XCK0/CLKO/OC0A/PCINT9
Name
PB0/ADC4/PCINT8
DDOV CLKO + (CKOUT • OC0A Enable • REMAP • OC0A) + (CKOUT • (OC0A
Enable + REMAP) • XCK0_MASTER • XCK0_OUT)
0
PVOE CKOUT(1)
0
PVOV (system clock)
0
PTOE
0
0
DIEOE (PCINT9 • PCIE1) + ADC5D + INT0
DIEOV (PCINT9 • PCIE1) + INT0
(PCINT8 • PCIE1) + ADC4D
(PCINT8 • PCIE1)
PCINT8 Input
DI
INT0/PCINT1 Input
ADC5
AIO
ADC4
Note:ꢀ
1. CKOUT is 1 when the configuration bit is “0” (Programmed).
14.5. Register Description
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14.5.1. Port A Input Pins Address
Name:ꢀ PINA
Offset:ꢀ 0x00
Reset:ꢀ N/A
Property:
ꢀ
Bit
7
PINA7
R/W
x
6
PINA6
R/W
x
5
PINA5
R/W
x
4
PINA4
R/W
x
3
PINA3
R/W
x
2
PINA2
R/W
x
1
PINA1
R/W
x
0
PINA0
R/W
x
Access
Reset
Bits 7:0 – PINAn:ꢀPort A Input Pins Address [n = 7:0]
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14.5.2. Port A Data Direction Register
Name:ꢀ DDRA
Offset:ꢀ 0x01
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
DDRA7
R/W
0
6
DDRA6
R/W
0
5
DDRA5
R/W
0
4
DDRA4
R/W
0
3
DDRA3
R/W
0
2
DDRA2
R/W
0
1
DDRA1
R/W
0
0
DDRA0
R/W
0
Access
Reset
Bits 7:0 – DDRAn:ꢀPort A Input Pins Address [n = 7:0]
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14.5.3. Port A Data Register
Name:ꢀ PORTA
Offset:ꢀ 0x02
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
PORTA7
R/W
6
PORTA6
R/W
5
PORTA5
R/W
4
PORTA4
R/W
3
PORTA3
R/W
2
PORTA2
R/W
1
PORTA1
R/W
0
PORTA0
R/W
Access
Reset
0
0
0
0
0
0
0
0
Bits 7:0 – PORTAn:ꢀPort A Data [n = 7:0]
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14.5.4. Port A Pull-up Enable Control Register
Name:ꢀ PUEA
Offset:ꢀ 0x03
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
PUEA7
R/W
0
6
PUEA6
R/W
0
5
PUEA5
R/W
0
4
PUEA4
R/W
0
3
PUEA3
R/W
0
2
PUEA2
R/W
0
1
PUEA1
R/W
0
0
PUEA0
R/W
0
Access
Reset
Bits 7:0 – PUEAn:ꢀPort A Input Pins Address [n = 7:0]
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14.5.5. Port B Input Pins Address
Name:ꢀ PINB
Offset:ꢀ 0x04
Reset:ꢀ N/A
Property:
ꢀ
Bit
7
6
5
4
3
PINB3
R/W
x
2
PINB2
R/W
x
1
PINB1
R/W
x
0
PINB0
R/W
x
Access
Reset
Bits 3:0 – PINBn:ꢀPort B Input Pins Address [n = 3:0]
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14.5.6. Port B Data Direction Register
Name:ꢀ DDRB
Offset:ꢀ 0x05
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
6
5
4
3
DDRB3
R/W
0
2
DDRB2
R/W
0
1
DDRB1
R/W
0
0
DDRB0
R/W
0
Access
Reset
Bits 3:0 – DDRBn:ꢀPort B Input Pins Address [n = 3:0]
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14.5.7. Port B Data Register
Name:ꢀ PORTB
Offset:ꢀ 0x06
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
6
5
4
3
PORTB3
R/W
2
PORTB2
R/W
1
PORTB1
R/W
0
PORTB0
R/W
Access
Reset
0
0
0
0
Bits 3:0 – PORTBn:ꢀPort B Data [n = 3:0]
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14.5.8. Port B Pull-up Enable Control Register
Name:ꢀ PUEB
Offset:ꢀ 0x07
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
6
5
4
3
PUEB3
R/W
0
2
PUEB2
R/W
0
1
PUEB1
R/W
0
0
PUEB0
R/W
0
Access
Reset
Bits 3:0 – PUEBn:ꢀPort B Input Pins Address [n = 3:0]
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14.5.9. Port Control Register
Name:ꢀ PORTCR
Offset:ꢀ 0x16
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
6
5
4
3
2
1
BBMB
R/W
0
0
BBMA
R/W
0
Access
Reset
Bit 1 – BBMB:ꢀBreak-Before-Make Mode Enable
When this bit is set the Break-Before-Make mode is activated for the entire Port B. The intermediate tri-
state cycle is then inserted when writing DDRxn to make an output.
Bit 0 – BBMA:ꢀBreak-Before-Make Mode Enable
When this bit is set the Break-Before-Make mode is activated for the entire Port A. The intermediate tri-
state cycle is then inserted when writing DDRxn to make an output.
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15.
USART - Universal Synchronous Asynchronous Receiver Transceiver
15.1. Overview
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is a highly
flexible serial communication device.
The USART can also be used in Master SPI mode. The Power Reduction USART bit in the Power
Reduction Register (0.PRUSARTn) must be written to '0' in order to enable USARTn. USART 0 in 0.
15.2. 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
Start Frame Detection
15.3. Block Diagram
In the USART Block Diagram, the CPU accessible I/O Registers and I/O pins are shown in bold. 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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Figure 15-1.ꢀUSART Block Diagram
Clock Generator
UBRRn[H:L]
OSC
BAUD RATE GENERATOR
SYNC LOGIC
PIN
CONTROL
XCKn
TxDn
RxDn
Transmitter
TX
CONTROL
UDRn(Transmit)
PARITY
GENERATOR
PIN
CONTROL
TRANSMIT SHIFT REGISTER
Receiver
CLOCK
RECOVERY
RX
CONTROL
DATA
RECOVERY
PIN
CONTROL
RECEIVE SHIFT REGISTER
PARITY
CHECKER
UDRn(Receive)
UCSRnA
UCSRnB
UCSRnC
Note:ꢀ Refer to the Pin Configurations and the I/O-Ports description for USART pin placement.
Related Links
Pin Descriptions on page 12
I/O-Ports on page 65
15.4. Clock Generation
The Clock Generation logic generates the base clock for the Transmitter and Receiver. The USART
supports four modes of clock operation: Normal asynchronous, Double Speed asynchronous, Master
synchronous and Slave synchronous mode. The USART Mode Select bit 0 in the USART Control and
Status Register n C (UCSRnC.UMSELn0) selects between asynchronous and synchronous operation.
Double Speed (asynchronous mode only) is controlled by the U2X0 found in the UCSRnA Register. When
using synchronous mode (UMSELn0=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.
Below is a block diagram of the clock generation logic.
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Figure 15-2.ꢀClock Generation Logic, Block Diagram
UBRRn
U2Xn
fosc
UBRRn+1
Prescaling
Down-Counter
/2
/4
/2
0
1
0
1
OSC
txclk
UMSELn
rxclk
DDR_XCKn
Sync
Register
Edge
Detector
xcki
0
1
XCKn
Pin
xcko
DDR_XCKn
UCPOLn
1
0
Signal description:
•
•
•
•
•
txclk: Transmitter clock (internal signal).
rxclk: Receiver base clock (internal signal).
xcki: Input from XCKn pin (internal signal). Used for synchronous slave operation.
xcko: Clock output to XCKn pin (internal signal). Used for synchronous master operation.
fosc: System clock frequency.
15.4.1. 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 the Clock Generation Logic block diagram in the previous section..
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 UMSEL, U2X0 and DDR_XCK bits.
The table below 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 15-1.ꢀEquations for Calculating Baud Rate Register Setting
Operating Mode
Equation for Calculating Baud
Rate(1)
Equation for Calculating UBRRn
Value
Asynchronous Normal mode
(U2X0 = 0)
ꢀ
ꢀ
OSC
OSC
BAUD =
ꢁꢂꢃꢃꢄ =
ꢁꢂꢃꢃꢄ =
ꢁꢂꢃꢃꢄ =
− 1
16 ꢁꢂꢃꢃꢄ + 1
16BAUD
Asynchronous Double Speed
mode (U2X0 = 1)
ꢀ
ꢀ
OSC
OSC
BAUD =
− 1
8 ꢁꢂꢃꢃꢄ + 1
8BAUD
Synchronous Master mode
ꢀ
ꢀ
OSC
OSC
BAUD =
− 1
2 ꢁꢂꢃꢃꢄ + 1
2BAUD
Note:ꢀ 1. The baud rate is defined to be the transfer rate in bits per second (bps)
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BAUD Baud rate (in bits per second, bps)
fOSC System oscillator clock frequency
UBRRn Contents of the UBRRnH and UBRRnL Registers, (0-4095).
Some examples of UBRRn values for some system clock frequencies are found in Examples
of Baud Rate Settings.
15.4.2. Double Speed Operation (U2X0)
The transfer rate can be doubled by setting the U2X0 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. However, in this case, the Receiver will 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.
15.4.3. External Clock
External clocking is used by the synchronous slave modes of operation. The description in this section
refers to the Clock Generation Logic block diagram in the previous section.
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:
ꢀ
OSC
ꢀ
<
XCKn
4
The value of 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.
15.4.4. Synchronous Clock Operation
When synchronous mode is used (UMSEL = 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 15-3.ꢀSynchronous Mode XCKn Timing
UCPOL = 1
XCKn
RxDn / TxDn
Sample
Sample
UCPOL = 0
XCKn
RxDn / TxDn
The UCPOL bit UCRSC selects which XCKn clock edge is used for data sampling and which is used for
data change. As the above timing diagram shows, when UCPOL is zero, the data will be changed at
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rising XCKn edge and sampled at falling XCKn edge. If UCPOL is set, the data will be changed at falling
XCKn edge and sampled at rising XCKn edge.
15.5. 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 data bits (from five up to nine data bits in total): first the
least significant data bit, then the next data bits ending with the most significant bit. If enabled, the parity
bit is inserted after the data bits, before the one or two 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. the
figure below illustrates the possible combinations of the frame formats. Bits inside brackets are optional.
Figure 15-4.ꢀFrame Formats
FRAME
(IDLE)
St
0
1
2
3
4
[5]
[6]
[7]
[8]
[P]
Sp
(St / IDLE)
St
(n)
P
Start bit, always low.
Data bits (0 to 8).
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:
•
•
•
Character Size bits (UCSRnC.UCSZn[2:0]) select the number of data bits in the frame.
Parity Mode bits (UCSRnC.UPMn[1:0]) enable and set the type of parity bit.
Stop Bit Select bit (UCSRnC.USBSn) select the number of stop bits. The Receiver ignores the
second stop bit.
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. An FE (Frame Error) will
only be detected in cases where the first stop bit is zero.
15.5.1. 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:
ꢅ
= ꢆ
⊕ … ⊕ ꢆ ⊕ ꢆ ⊕ ꢆ ⊕ ꢆ ⊕ 0ꢅ
= ꢆ
⊕ … ⊕ ꢆ ⊕ ꢆ ⊕ ꢆ ⊕ ꢆ ⊕ 1
ꢄ + − 1 3 2 1 0
even
ꢄ + − 1
3
2
1
0
odd
Peven
Parity bit using even parity
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Podd
Parity bit using odd parity
dn
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.
15.6. 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 interrupts globally disabled) when doing the initialization.
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 TXC Flag (UCSRnA.TXC) 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. The UCSRnA.TXC 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
USART_Init:
; Set baud rate to UBRR0
out
out
UBRR0H, r17
UBRR0L, r16
; Enable receiver and transmitter
ldi
out
r16, (1<<RXEN0)|(1<<TXEN0)
UCSR0B,r16
; Set frame format: 8data, 2stop bit
ldi
out
ret
r16, (1<<USBS0)|(3<<UCSZ00)
UCSR0C,r16
C Code Example
#define FOSC 1843200 // Clock Speed
#define BAUD 9600
#define MYUBRR FOSC/16/BAUD-1
void main( void )
{
...
USART_Init(MYUBRR)
...
}
void USART_Init( unsigned int ubrr)
{
/*Set baud rate */
UBRR0H = (unsigned char)(ubrr>>8);
UBRR0L = (unsigned char)ubrr;
Enable receiver and transmitter */
UCSR0B = (1<<RXEN0)|(1<<TXEN0);
/* Set frame format: 8data, 2stop bit */
UCSR0C = (1<<USBS0)|(3<<UCSZ00);
}
More advanced initialization routines can be written to include frame format as
parameters, disable interrupts, and so on. However, many applications use a fixed setting
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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.
15.7. 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.
15.7.1. Sending Frames with 5 to 8 Data Bits
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, U2X0 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 (UDRE) Flag. When using frames with less than eight bits, the
most significant bits written to the UDR0 are ignored. The USART 0 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 R17.
Assembly Code Example
USART_Transmit:
; Wait for empty transmit buffer
in
sbrs
rjmp
r17, UCSR0A
r17, UDRE
USART_Transmit
; Put data (r16) into buffer, sends the data
out
ret
UDR0,r16
C Code Example
void USART_Transmit( unsigned char data )
{
/* Wait for empty transmit buffer */
while ( !( UCSR0A & (1<<UDRE)) )
;
/* Put data into buffer, sends the data */
UDR0 = data;
}
The function simply waits for the transmit buffer to be empty by checking the UDRE 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.
15.7.2. 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.
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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.
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
USART_Transmit:
; Wait for empty transmit buffer
in
sbrs
rjmp
r18, UCSR0A
r18, UDRE
USART_Transmit
; Copy 9th bit from r17 to TXB8
cbi
sbrc
sbi
UCSR0B,TXB8
r17,0
UCSR0B,TXB8
; Put LSB data (r16) into buffer, sends the data
out
ret
UDR0,r16
C Code Example
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSR0A & (1<<UDRE))) )
;
/* Copy 9th bit to TXB8 */
UCSR0B &= ~(1<<TXB8);
if ( data & 0x0100 )
UCSR0B |= (1<<TXB8);
/* Put data into buffer, sends the data */
UDR0 = data;
}
Note:ꢀ 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.
15.7.3. Transmitter Flags and Interrupts
The USART Transmitter has two flags that indicate its state: USART Data Register Empty (UDRE) and
Transmit Complete (TXC). Both flags can be used for generating interrupts.
The Data Register Empty (UDRE) 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 (UDRIE) bit in UCSRnB is written to '1', the USART Data
Register Empty Interrupt will be executed as long as UDRE is set (provided that global interrupts are
enabled). UDRE 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 UDRE or disable
the Data Register Empty interrupt - otherwise, a new interrupt will occur once the interrupt routine
terminates.
The Transmit Complete (TXC) 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. The TXC Flag bit is
either automatically cleared when a transmit complete interrupt is executed, or it can be cleared by writing
a '1' to its bit location. The TXC Flag is useful in half-duplex communication interfaces (like the RS-485
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standard), where a transmitting application must enter receive mode and free the communication bus
immediately after completing the transmission.
When the Transmit Compete Interrupt Enable (TXCIE) bit in UCSRnB is written to '1', the USART
Transmit Complete Interrupt will be executed when the TXC 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 TXC Flag, this is done automatically when the interrupt is executed.
15.7.4. Parity Generator
The Parity Generator calculates the parity bit for the serial frame data. When parity bit is enabled
(UCSRnC.UPM[1]=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.
15.7.5. Disabling the Transmitter
When writing the TX Enable bit in the USART Control and Status Register n B (UCSRnB.TXEN) to zero,
the disabling of the Transmitter 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.
15.8. Data Reception – The USART Receiver
The USART Receiver is enabled by writing the Receive Enable (RXEN) bit in the UCSRnB Register to '1'.
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.
15.8.1. 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.
The following code example shows a simple USART receive function based on polling of
the Receive Complete (RXC) Flag. When using frames with less than eight bits the most
significant bits of the data read from the UDR0 will be masked to zero. The USART 0 has
to be initialized before the function can be used. For the assembly code, the received
data will be stored in R16 after the code completes.
Assembly Code Example
USART_Receive:
; Wait for data to be received
in
r17, UCSR0A
sbrs r17, RXC
rjmp USART_Receive
; Get and return received data from buffer
in
ret
r16, UDR0
C Code Example
unsigned char USART_Receive( void )
{
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/* Wait for data to be received */
while ( !(UCSR0A & (1<<RXC)) )
;
/* Get and return received data from buffer */
return UDR0;
}
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 function simply waits for data to be present in the receive buffer by checking the
RXC Flag, before reading the buffer and returning the value.
15.8.2. Receiving Frames with 9 Data Bits
If 9-bit characters are used (UCSZn=7) the ninth bit must be read from the RXB8 bit in UCSRnB before
reading the low bits from the UDRn. This rule applies to the FE, DOR and UPE 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 TXB8, FE, DOR and UPE bits, which all are stored in the
FIFO, will change.
The following code example shows a simple receive function for USART0 that handles
both nine bit characters and the status bits. For the assembly code, the received data will
be stored in R17:R16 after the code completes.
Assembly Code Example
USART_Receive:
; Wait for data to be received
in
sbrs
rjmp
r16, UCSR0A
r16, RXC
USART_Receive
; Get status and 9th bit, then data from buffer
in
in
in
r18, UCSR0A
r17, UCSR0B
r16, UDR0
; If error, return -1
andi
breq
ldi
r18,(1<<FE)|(1<<DOR)|(1<<UPE)
USART_ReceiveNoError
r17, HIGH(-1)
r16, LOW(-1)
ldi
USART_ReceiveNoError:
; Filter the 9th bit, then return
lsr
andi
ret
r17
r17, 0x01
C Code Example
unsigned int USART_Receive( void )
{
unsigned char status, resh, resl;
/* Wait for data to be received */
while ( !(UCSR0A & (1<<RXC)) )
;
/* Get status and 9th bit, then data */
/* from buffer */
status = UCSR0A;
resh = UCSR0B;
resl = UDR0;
/* If error, return -1 */
if ( status & (1<<FE)|(1<<DOR)|(1<<UPE) )
return -1;
/* Filter the 9th bit, then return */
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resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
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.
15.8.3. Receive Compete Flag and Interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXC) Flag indicates if there are unread data present in the receive buffer. This
flag is one when unreadꢀdata 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 (RXEN = 0), the receive buffer will be
flushed and consequently the RXCn bit will become zero.
When the Receive Complete Interrupt Enable (RXCIE) in UCSRnB is set, the USART Receive Complete
interrupt will be executed as long as the RXC 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 UDR in order to clear the RXC Flag, otherwise a new interrupt will occur once the interrupt routine
terminates.
15.8.4. Receiver Error Flags
The USART Receiver has three Error Flags: Frame Error (FE), Data OverRun (DOR) and Parity Error
(UPE). 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 (FE) Flag indicates the state of the first stop bit of the next readable frame stored in the
receive buffer. The FE Flag is zero when the stop bit was correctly read as '1', and the FE 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 FE Flag is not affected by the setting of the USBS
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 (DOR) Flag indicates data loss due to a receiver buffer full condition. A Data OverRun
occurs when the receive buffer is full (two characters), a new character is waiting in the Receive Shift
Register, and a new start bit is detected. If the DOR Flag is set, one or more serial frames were lost
between the last frame read from UDR, and the next frame read from UDR. For compatibility with future
devices, always write this bit to zero when writing to UCSRnA. The DOR Flag is cleared when the frame
received was successfully moved from the Shift Register to the receive buffer.
The Parity Error (UPE) Flag indicates that the next frame in the receive buffer had a Parity Error when
received. If Parity Check is not enabled the UPE bit will always read '0'. For compatibility with future
devices, always set this bit to zero when writing to UCSRnA. For more details see Parity Bit Calculation
and 'Parity Checker' below.
15.8.5. Parity Checker
The Parity Checker is active when the high USART Parity Mode bit 1 in the USART Control and Status
Register n C (UCSRnC.UPM[1]) is written to '1'. The type of Parity Check to be performed (odd or even)
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is selected by the UCSRnC.UPM[0] 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 USART
Parity Error Flag in the USART Control and Status Register n A (UCSRnA.UPE) 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 (UPM[1] = 1). This bit is valid until the receive
buffer (UDRn) is read.
15.8.6. 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., UCSRnB.RXEN is written 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.
15.8.7. 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 shows how to flush the receive buffer of USART0.
Assembly Code Example
USART_Flush:
in
r16, UCSR0A
r16, RXC
sbrs
ret
in
r16, UDR0
USART_Flush
rjmp
C Code Example
void USART_Flush( void )
{
unsigned char dummy;
while ( UCSR0A & (1<<RXC) ) dummy = UDR0;
}
15.9. 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.
15.9.1. Asynchronous Clock Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. The figure below
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 8 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
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using the Double Speed mode (UCSRnA.U2X0=1) of operation. Samples denoted '0' are samples taken
while the RxDn line is idle (i.e., no communication activity).
Figure 15-5.ꢀStart Bit Sampling
RxDn
IDLE
START
BIT 0
Sample
(U2X = 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)
0
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 on RxDn. 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.
15.9.2. 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. The figure below 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 15-6.ꢀSampling of Data and Parity Bit
RxDn
BIT n
Sample
(U2X = 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
Sample
(U2X = 1)
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: If two or all three center samples (those marked by
their sample number inside boxes) 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. The Receiver only uses the first
stop bit of a frame.
The following figure shows the sampling of the stop bit and the earliest possible beginning of the start bit
of the next frame.
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Figure 15-7.ꢀStop Bit Sampling and Next Start Bit Sampling
(A)
(B)
(C)
RxD
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 (UCSRnA.FE) 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 taken at point marked
(A) in the figure above. 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.
15.9.3. 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 base frequency (see
recommendations below), 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.
ꢈ + 1 ꢉ
ꢉ − 1 + ꢈ ⋅ ꢉ + ꢉ
ꢈ + 2 ꢉ
ꢈ + 1 ꢉ + ꢉ
ꢇ
=
ꢇ
=
fast
slow
ꢊ
ꢋ
•
D: Sum of character size and parity size (D = 5 to 10 bit)
•
•
S: 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.
The following tables list the maximum receiver baud rate error that can be tolerated. Note that Normal
Speed mode has higher toleration of baud rate variations.
Table 15-2.ꢀRecommended Maximum Receiver Baud Rate Error for Normal Speed Mode (U2X0 = 0)
D
Rslow [%] Rfast [%] Max. Total Error [%] Recommended Max. Receiver Error [%]
# (Data+Parity Bit)
5
6
7
8
93.20
94.12
94.81
95.36
106.67
105.79
105.11
104.58
+6.67/-6.8
+5.79/-5.88
+5.11/-5.19
+4.58/-4.54
±3.0
±2.5
±2.0
±2.0
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D
Rslow [%] Rfast [%] Max. Total Error [%] Recommended Max. Receiver Error [%]
# (Data+Parity Bit)
9
95.81
96.17
104.14
103.78
+4.14/-4.19
+3.78/-3.83
±1.5
±1.5
10
Table 15-3.ꢀRecommended Maximum Receiver Baud Rate Error for Double Speed Mode (U2X0 = 1)
D
Rslow [%] Rfast [%] Max Total Error [%] Recommended Max Receiver Error [%]
# (Data+Parity Bit)
5
94.12
94.92
95.52
96.00
96.39
96.70
105.66
104.92
104,35
103.90
103.53
103.23
+5.66/-5.88
+4.92/-5.08
+4.35/-4.48
+3.90/-4.00
+3.53/-3.61
+3.23/-3.30
±2.5
±2.0
±1.5
±1.5
±1.5
±1.0
6
7
8
9
10
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 (EXTCLK)
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 resonator's 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 UBRRn value that gives an acceptable low error can be used if
possible.
15.9.4. Start Frame Detection
The USART start frame detector can wake up the MCU from Power-down and Standby sleep mode when
it detects a start bit.
When a high-to-low transition is detected on RxDn, the internal 8MHz oscillator is powered up and the
USART clock is enabled. After start-up the rest of the data frame can be received, provided that the baud
rate is slow enough in relation to the internal 8MHz oscillator start-up time. Start-up time of the internal
8MHz oscillator varies with supply voltage and temperature.
The USART start frame detection works both in asynchronous and synchronous modes. It is enabled by
writing the Start Frame Detection Enable bit (SFDE). If the USART Start Interrupt Enable (RXSIE) bit is
set, the USART Receive Start Interrupt is generated immediately when start is detected.
When using the feature without start interrupt, the start detection logic activates the internal 8MHz
oscillator and the USART clock while the frame is being received, only. Other clocks remain stopped until
the Receive Complete Interrupt wakes up the MCU.
The maximum baud rate in synchronous mode depends on the sleep mode the device is woken up from,
as follows:
•
•
Idle sleep mode: system clock frequency divided by four
Standby or Power-down: 500kbps
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The maximum baud rate in asynchronous mode depends on the sleep mode the device is woken up from,
as follows:
•
Idle sleep mode: the same as in active mode
Table 15-4.ꢀMaximum Total Baudrate Error in Normal Speed Mode
Baudrate
Frame Size
5
6
7
8
9
10
0 - 28.8kbps
38.4kbps
57.6kbps
76.8kbps
115.2kbps
+6.67
-5.88
+5.79
-5.08
+5.11
-4.48
+4.58
-4.00
+4.14
-3.61
+3.78
-3.30
+6.63
-5.88
+5.75
-5.08
+5.08
-4.48
+4.55
-4.00
+4.12
-3.61
+3.76
-3.30
+6.10
-5.88
+5.30
-5.08
+4.69
-4.48
+4.20
-4.00
+3.80
-3.61
+3.47
-3.30
+5.59
-5.88
+4.85
-5.08
+4.29
-4.48
+3.85
-4.00
+3.48
-3.61
+3.18
-3.30
+4.57
-5.88
+3.97
-5.08
+3.51
-4.48
+3.15
-4.00
+2.86
-3.61
+2.61
-3.30
Table 15-5.ꢀMaximum Total Baudrate Error in Double Speed Mode
Baudrate
Frame Size
5
6
7
8
9
10
0 - 57.6kbps
76.8kbps
+5.66
-4.00
+4.92
-3.45
+4.35
-3.03
+3.90
-2.70
+3.53
-2.44
+3.23
-2.22
+5.59
-4.00
+4.85
-3.45
+4.29
-3.03
+3.85
-2.70
+3.48
-2.44
+3.18
-2.22
115.2kbps
+4.57
-4.00
+3.97
-3.45
+3.51
-3.03
+3.15
-2.70
+2.86
-2.44
+2.61
-2.22
Related Links
UCSR0D on page 117
15.10. 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 9 data bits, then
the ninth bit (RXB8) is used for identifying address and data frames. When the frame type bit (the first
stop or the ninth bit) is '1', the frame contains an address. When the frame type bit is '0', the frame is a
data frame.
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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.
15.10.1. Using MPCMn
For an MCU to act as a master MCU, it can use a 9-bit character frame format (UCSZ1=7). The ninth bit
(TXB8) must be set when an address frame (TXB8=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 (MPCM 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 RXC 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 MPCM bit in UCSRnA, otherwise it waits for the next address byte and keeps the MPCM
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 MPCM bit set, will ignore the data frames.
5. When the last data frame is received by the addressed MCU, the addressed MCU sets the MPCM
bit and waits for a new address frame from master. The process then repeats from step 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 (USBS = 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 MPCM bit. The MPCM bit
shares the same I/O location as the TXC Flag and this might accidentally be cleared when using SBI or
CBI instructions.
15.11. 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 UBRRn settings as listed in the table below.
UBRRn 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 also section Asynchronous Operational
Range). The error values are calculated using the following equation:
2
BaudRate
Closest Match
ꢌꢍꢍꢎꢍ %
=
− 1 100 %
BaudRate
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Table 15-6.ꢀExamples of UBRRn Settings for Commonly Used Oscillator Frequencies
Baud
Rate
[bps]
fosc = 1.0000MHz
U2X0 = 0
fosc = 1.8432MHz
U2X0 = 0
fosc = 2.0000MHz
U2X0 = 0 U2X0 = 1
U2X0 = 1
U2X0 = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400
25
12
6
0.2%
0.2%
51
25
0.2%
0.2%
0.2%
-3.5%
-7.0%
8.5%
8.5%
8.5%
47
23
11
7
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
95
47
23
15
11
7
0.0% 51
0.0% 25
0.0% 12
0.0% 8
0.0% 6
0.0% 3
0.0% 2
0.0% 1
0.0% 1
0.0% 0
0.0% –
0.2%
0.2%
0.2%
103
51
0.2%
0.2%
0.2%
2.1%
0.2%
-3.5%
-7.0%
8.5%
8.5%
8.5%
–
4800
9600
-7.0% 12
25
14.4k
19.2k
28.8k
38.4k
57.6k
76.8k
115.2k
230.4k
250k
3
8.5%
8.5%
8.5%
8
6
3
-3.5% 16
-7.0% 12
2
5
1
3
8.5%
8.5%
8.5%
8
6
3
1
-18.6% 2
2
5
0
8.5%
1
1
3
–
–
–
–
–
1
-18.6% 1
-25.0% 2
-18.6% 2
–
0
8.5%
0
–
–
0.0%
1
0
–
8.5%
1
–
–
–
–
–
–
–
–
–
–
–
–
–
0
0.0%
Max.(1) 62.5kbps
125kbps
115.2kbps
230.4kbps
125kbps
250kbps
Note: 1. UBRRn = 0, Error = 0.0%
Table 15-7.ꢀExamples of UBRRn Settings for Commonly Used Oscillator Frequencies
Baud Rate
[bps]
fosc = 3.6864MHz
U2X0 = 0 U2X0 = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
fosc = 4.0000MHz
fosc = 7.3728MHz
U2X0 = 0 U2X0 = 1
U2X0 = 0 U2X0 = 1
2400
95
47
23
15
11
7
0.0% 191
0.0% 95
0.0% 47
0.0% 31
0.0% 23
0.0% 15
0.0% 11
0.0% 103
0.0% 51
0.0% 25
0.0% 16
0.0% 12
0.2% 207
0.2% 103
0.2% 51
2.1% 34
0.2% 25
-3.5% 16
-7.0% 12
0.2% 191
0.2% 95
0.2% 47
-0.8% 31
0.2% 23
2.1% 15
0.2% 11
-3.5% 7
0.0% 383
0.0% 191
0.0% 95
0.0% 63
0.0% 47
0.0% 31
0.0% 23
0.0% 15
0.0% 11
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
4800
9600
14.4k
19.2k
28.8k
38.4k
57.6k
76.8k
115.2k
230.4k
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
8
6
3
2
1
0
5
3
0.0%
0.0%
0.0%
0.0%
7
5
3
1
8.5%
8.5%
8.5%
8.5%
8
6
3
1
2
-7.0% 5
1
8.5%
8.5%
3
1
0.0%
0.0%
7
3
0
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Baud Rate
[bps]
fosc = 3.6864MHz
U2X0 = 0 U2X0 = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
fosc = 4.0000MHz
fosc = 7.3728MHz
U2X0 = 0 U2X0 = 1
U2X0 = 0 U2X0 = 1
250k
0.5M
1M
0
–
–
-7.8% 1
-7.8% 0
-7.8% –
0.0%
1
0.0%
0.0%
–
1
0
–
-7.8% 3
-7.8% 1
-7.8%
-7.8%
-7.8%
–
–
0
–
–
–
0
–
–
–
–
0
Max.(1)
230.4kbps
460.8kbps
250kbps
0.5Mbps
460.8kbps
921.6kbps
(1) UBRRn = 0, Error = 0.0%
Table 15-8.ꢀExamples of UBRRn Settings for Commonly Used Oscillator Frequencies
Baud Rate
[bps]
fosc = 8.0000MHz
U2X0 = 0 U2X0 = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
fosc = 11.0592MHz
fosc = 14.7456MHz
U2X0 = 0 U2X0 = 1
U2X0 = 0 U2X0 = 1
2400
4800
9600
14.4k
19.2k
28.8k
38.4k
57.6k
76.8k
115.2k
230.4k
250k
207
0.2% 416
0.2% 207
0.2% 103
-0.8% 68
0.2% 51
2.1% 34
0.2% 25
-3.5% 16
-7.0% 12
-0.1% 287
0.2% 143
0.2% 71
0.6% 47
0.2% 35
-0.8% 23
0.2% 17
2.1% 11
0.0% 575
0.0% 287
0.0% 143
0.0% 95
0.0% 71
0.0% 47
0.0% 35
0.0% 23
0.0% 17
0.0% 11
0.0% 383
0.0% 191
0.0% 95
0.0% 63
0.0% 47
0.0% 31
0.0% 23
0.0% 15
0.0% 11
0.0% 767
0.0% 383
0.0% 191
0.0% 127
0.0% 95
0.0% 63
0.0% 47
0.0% 31
0.0% 23
0.0% 15
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%
103
51
34
25
16
12
8
6
0.2%
8
3
8.5%
8.5%
0.0%
0.0%
–
8
-3.5% 5
0.0%
0.0%
7
3
1
3
8.5%
0.0%
0.0%
0.0%
2
2
–
–
0.0%
5
0.0% 7
1
3
-7.8% 5
-7.8% 3
-7.8% 1
-7.8% 6
-7.8% 3
-7.8% 1
0.5M
1M
0
1
–
–
2
–
–
0
–
0
Max.(1)
0.5Mbps
1Mbps
691.2kbps
1.3824Mbps
921.6kbps
1.8432Mbps
(1) UBRRn = 0, Error = 0.0%
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Table 15-9.ꢀExamples of UBRRn Settings for Commonly Used Oscillator Frequencies
Baud Rate
[bps]
fosc = 16.0000MHz
U2X0 = 0 U2X0 = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
fosc = 18.4320MHz
fosc = 20.0000MHz
U2X0 = 0 U2X0 = 1
U2X0 = 0 U2X0 = 1
2400
4800
9600
14.4k
19.2k
28.8k
38.4k
57.6k
76.8k
115.2k
230.4k
250k
416
207
103
68
51
34
25
16
12
8
-0.1% 832
0.2% 416
0.2% 207
0.6% 138
0.2% 103
-0.8% 68
0.2% 51
2.1% 34
0.2% 25
-3.5% 16
0.0% 479
-0.1% 239
0.2% 119
-0.1% 79
0.2% 59
0.6% 39
0.2% 29
-0.8% 19
0.2% 14
0.0% 959
0.0% 479
0.0% 239
0.0% 159
0.0% 119
0.0% 79
0.0% 59
0.0% 39
0.0% 29
0.0% 19
0.0% 520
0.0% 259
0.0% 129
0.0% 86
0.0% 64
0.0% 42
0.0% 32
0.0% 21
0.0% 15
0.0% 10
0.0% 1041
0.2% 520
0.2% 259
-0.2% 173
0.2% 129
0.9% 86
-1.4% 64
-1.4% 42
1.7% 32
-1.4% 21
8.5% 10
0.0%
0.0%
0.2%
-0.2%
0.2%
-0.2%
0.2%
0.9%
-1.4%
-1.4%
-1.4%
0.0%
0.0%
–
2.1%
9
3
8.5%
0.0%
0.0%
0.0%
8
-3.5% 4
0.0%
9
0.0%
2.4%
4
4
3
7
0.0%
0.0%
0.0%
4
–
–
-7.8% 8
0.0%
9
0.5M
1M
1
3
–
–
4
–
-7.8% –
–
–
4
0
1
–
–
–
Max.(1)
1Mbps
2Mbps
1.152Mbps
2.304Mbps
1.25Mbps
2.5Mbps
(1) UBRRn = 0, Error = 0.0%
15.12. Register Description
All of USART registers are NOT accessible using SBI and CBI instructions.
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15.12.1. USART I/O Data Register 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 UDR0. The Transmit Data Buffer Register (TXB) will
be the destination for data written to the UDR0 Register location. Reading the UDR0 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 UDRE0 Flag in the UCSR0A Register is set. Data
written to UDR0 when the UDRE0 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
TxD0 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.
Name:ꢀ UDR0
Offset:ꢀ 0x08
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
TXB / RXB[7:0]
Access
Reset
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 – TXB / RXB[7:0]:ꢀUSART Transmit / Receive Data Buffer
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15.12.2. USART Control and Status Register 0 A
Name:ꢀ UCSR0A
Offset:ꢀ 0x0E
Reset:ꢀ 0x20
Property: -
ꢀ
Bit
7
RXC0
R
6
TXC0
R/W
0
5
4
FE0
R
3
DOR0
R
2
UPE0
R
1
U2X0
R/W
0
0
MPCM0
R/W
0
UDRE0
Access
Reset
R
1
0
0
0
0
Bit 7 – RXC0:ꢀ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 RXC0 bit will become zero. The RXC0 Flag can be used to generate a
Receive Complete interrupt (see description of the RXCIE0 bit).
Bit 6 – TXC0:ꢀ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 (UDR0). The TXC0 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
TXC0 Flag can generate a Transmit Complete interrupt (see description of the TXCIE0 bit).
Bit 5 – UDRE0:ꢀUSART Data Register Empty
The UDRE0 Flag indicates if the transmit buffer (UDR0) is ready to receive new data. If UDRE0 is one,
the buffer is empty, and therefore ready to be written. The UDRE0 Flag can generate a Data Register
Empty interrupt (see description of the UDRIE0 bit). UDRE0 is set after a reset to indicate that the
Transmitter is ready.
Bit 4 – FE0:ꢀ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
(UDR0) 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 UCSR0A.
This bit is reserved in Master SPI Mode (MSPIM).
Bit 3 – DOR0:ꢀData OverRun
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), a new character is waiting in the Receive
Shift Register, and a new start bit is detected.
If this bit is set, one or more serial frames were lost between the last frame 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. This bit is cleared when the frame received was successfully moved from the Shift Register to
the receive buffer.
This bit is reserved in Master SPI Mode (MSPIM).
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Bit 2 – UPE0:ꢀ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 (UPM0 = 1). This bit is valid until the receive buffer (UDR0) is read.
Always set this bit to zero when writing to UCSR0A.
This bit is reserved in Master SPI Mode (MSPIM).
Bit 1 – U2X0:ꢀ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.
This bit is reserved in Master SPI Mode (MSPIM).
Bit 0 – MPCM0:ꢀ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 MPCM0 setting.
This bit is reserved in Master SPI Mode (MSPIM).
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15.12.3. USART Control and Status Register 0 B
Name:ꢀ UCSR0B
Offset:ꢀ 0x0D
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
RXCIE0
R/W
0
6
TXCIE0
R/W
0
5
UDRIE0
R/W
0
4
RXEN0
R/W
0
3
TXEN0
R/W
0
2
UCSZ02
R/W
0
1
0
TXB80
R/W
0
RXB80
Access
Reset
R
0
Bit 7 – RXCIE0:ꢀRX Complete Interrupt Enable 0
Writing this bit to one enables interrupt on the RXC0 Flag. A USART Receive Complete interrupt will be
generated only if the RXCIE0 bit is written to one, the Global Interrupt Flag in SREG is written to one and
the RXC0 bit in UCSR0A is set.
Bit 6 – TXCIE0:ꢀTX Complete Interrupt Enable 0
Writing this bit to one enables interrupt on the TXC0 Flag. A USART Transmit Complete interrupt will be
generated only if the TXCIE0 bit is written to one, the Global Interrupt Flag in SREG is written to one and
the TXC0 bit in UCSR0A is set.
Bit 5 – UDRIE0:ꢀUSART Data Register Empty Interrupt Enable 0
Writing this bit to one enables interrupt on the UDRE0 Flag. A Data Register Empty interrupt will be
generated only if the UDRIE0 bit is written to one, the Global Interrupt Flag in SREG is written to one and
the UDRE0 bit in UCSR0A is set.
Bit 4 – RXEN0:ꢀReceiver Enable 0
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 FE0,
DOR0, and UPE0 Flags.
Bit 3 – TXEN0:ꢀTransmitter Enable 0
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port operation
for the TxD0 pin when enabled. The disabling of the Transmitter (writing TXEN0 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 TxD0 port.
Bit 2 – UCSZ02:ꢀCharacter Size 0
The UCSZ02 bits combined with the UCSZ0[1:0] bit in UCSR0C sets the number of data bits (Character
Size) in a frame the Receiver and Transmitter use.
This bit is reserved in Master SPI Mode (MSPIM).
Bit 1 – RXB80:ꢀReceive Data Bit 8 0
RXB80 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 UDR0.
This bit is reserved in Master SPI Mode (MSPIM).
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Bit 0 – TXB80:ꢀTransmit Data Bit 8 0
TXB80 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 UDR0.
This bit is reserved in Master SPI Mode (MSPIM).
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15.12.4. USART Control and Status Register 0 C
Name:ꢀ UCSR0C
Offset:ꢀ 0x0C
Reset:ꢀ 0x06
Property: -
ꢀ
Bit
7
6
5
4
3
2
UCSZ01 /
UDORD0
R/W
1
UCSZ00 /
UCPHA0
R/W
0
UMSEL01
UMSEL00
UPM01
UPM00
USBS0
UCPOL0
Access
Reset
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
1
1
Bits 7:6 – UMSEL0n:ꢀUSART Mode Select 0 n [n = 1:0]
These bits select the mode of operation of the USART0
Table 15-10.ꢀUSART Mode Selection
UMSEL0[1:0]
Mode
00
01
10
11
Asynchronous USART
Synchronous USART
Reserved
Master SPI (MSPIM)(1)
Note:ꢀ
1. The UDORD0, UCPHA0, and UCPOL0 can be set in the same write operation where the MSPIM is
enabled.
Bits 5:4 – UPM0n:ꢀUSART Parity Mode 0 n [n = 1:0]
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 UPM0 setting. If a mismatch is
detected, the UPE0 Flag in UCSR0A will be set.
Table 15-11.ꢀUSART Mode Selection
UPM0[1:0]
ParityMode
00
01
10
11
Disabled
Reserved
Enabled, Even Parity
Enabled, Odd Parity
These bits are reserved in Master SPI Mode (MSPIM).
Bit 3 – USBS0:ꢀUSART Stop Bit Select 0
This bit selects the number of stop bits to be inserted by the Transmitter. The Receiver ignores this
setting.
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Table 15-12.ꢀStop Bit Settings
USBS0
Stop Bit(s)
1-bit
0
1
2-bit
This bit is reserved in Master SPI Mode (MSPIM).
Bit 2 – UCSZ01 / UDORD0:ꢀUSART Character Size / Data Order
UCSZ0[1:0]: USART Modes: The UCSZ0[1:0] bits combined with the UCSZ02 bit in UCSR0B sets the
number of data bits (Character Size) in a frame the Receiver and Transmitter use.
Table 15-13.ꢀCharacter Size Settings
UCSZ0[2:0]
000
Character Size
5-bit
001
6-bit
010
7-bit
011
8-bit
100
Reserved
Reserved
Reserved
9-bit
101
110
111
UDPRD0: Master SPI Mode: 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 USART in SPI Mode - Frame Formats for
details.
Bit 1 – UCSZ00 / UCPHA0:ꢀUSART Character Size / Clock Phase
UCSZ00: USART Modes: Refer to UCSZ01.
UCPHA0: Master SPI Mode: The UCPHA0 bit setting determine if data is sampled on the leasing edge
(first) or tailing (last) edge of XCK0. Refer to the SPI Data Modes and Timing for details.
Bit 0 – UCPOL0:ꢀClock Polarity 0
USART0 Modes: This bit is used for synchronous mode only. Write this bit to zero when asynchronous
mode is used. The UCPOL0 bit sets the relationship between data output change and data input sample,
and the synchronous clock (XCK0).
Table 15-14.ꢀUSART Clock Polarity Settings
UCPOL0 Transmitted Data Changed (Output of TxD0 Received Data Sampled (Input on RxD0
Pin)
Pin)
0
1
Rising XCK0 Edge
Falling XCK0 Edge
Falling XCK0 Edge
Rising XCK0 Edge
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Master SPI Mode: The UCPOL0 bit sets the polarity of the XCK0 clock. The combination of the UCPOL0
and UCPHA0 bit settings determine the timing of the data transfer. Refer to the SPI Data Modes and
Timing for details.
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15.12.5. USART Control and Status Register 0 D
This register is not used in Master SPI Mode (UMSEL0[1:0] = 11)
Name:ꢀ UCSR0D
Offset:ꢀ 0x0B
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
RXSIE
R/W
0
6
5
SFDE
R/W
0
4
3
2
1
0
RXS
R/W
0
Access
Reset
Bit 7 – RXSIE:ꢀUSART RX Start Interrupt Enable
Writing this bit to one enables the interrupt on the RXS flag. In sleep modes this bit enables start frame
detector that can wake up the MCU when a start condition is detected on the RxD line. The USART RX
Start Interrupt is generated only, if the RXSIE bit, the Global Interrupt flag, and RXS are set.
Bit 6 – RXS:ꢀUSART RX Start
The RXS flag is set when a start condition is detected on the RxD line. If the RXSIE bit and the Global
Interrupt Enable flag are set, an RX Start Interrupt will be generated when the flag is set. The flag can
only be cleared by writing a logical one on the RXS bit location.
If the start frame detector is enabled (RXSIE = 1) and the Global Interrupt Enable flag is set, the RX Start
Interrupt will wake up the MCU from all sleep modes.
Bit 5 – SFDE:ꢀStart Frame Detection Enable
Writing this bit to one enables the USART Start Frame Detection mode. The start frame detector is able to
wake up the MCU from sleep mode when a start condition, i.e. a high (IDLE) to low (START) transition, is
detected on the RxD line.
Table 15-15.ꢀUSART Start Frame Detection Modes
UCSR0D.SFDE UCSR0D.RXSIE UCSR0B.RXCIE Description
0
1
1
X
0
0
X
0
1
Start frame detector disabled
Reserved
Start frame detector enabled. RXC flag wakes up
MCU from all sleep modes
1
1
1
1
0
1
Start frame detector enabled. RXS flag wakes up
MCU from all sleep modes
Start frame detector enabled. Both RXC and RXS
wake up the MCU from all sleep modes
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15.12.6. USART Baud Rate 0 Register Low and High byte
The UBRR0L and UBRR0H register pair represents the 16-bit value, UBRR0.The low byte [7:0] (suffix L)
is accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset + 0x01. For
more details on reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
Name:ꢀ UBRR0L and UBRR0H
Offset:ꢀ 0x09
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
15
14
13
12
11
10
9
8
UBRR0[11:8]
Access
Reset
R/W
0
R/W
0
R/W
0
R/W
0
Bit
7
6
5
4
3
2
1
0
UBRR0[7:0]
Access
Reset
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 11:0 – UBRR0[11:0]:ꢀUSART Baud Rate
This is a 12-bit register which contains the USART baud rate. The UBRR0H contains the four most
significant bits and the UBRR0L contains the eight least significant bits of the USART 0 baud rate.
Ongoing transmissions by the Transmitter and Receiver will be corrupted if the baud rate is changed.
Writing UBRR0L will trigger an immediate update of the baud rate prescaler.
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16.
USARTSPI - USART in SPI Mode
16.1. Overview
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) can be set to a
master SPI compliant mode of operation.
Setting both UMSELn[1:0] 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.
16.2. 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
16.3. 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 table below contains the equations for calculating the baud rate or UBRRn setting for Synchronous
Master Mode.
Table 16-1.ꢀEquations for Calculating Baud Rate Register Setting
Operating Mode
Equation for Calculating Baud
Rate(1)
Equation for Calculating UBRRn
Value
Synchronous Master
mode
ꢀ
ꢀ
OSC
OSC
BAUD =
ꢁꢂꢃꢃꢄ =
− 1
2 ꢁꢂꢃꢃꢄ + 1
2BAUD
Note: 1. The baud rate is defined to be the transfer rate in bit per second (bps)
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BAUD
fOSC
Baud rate (in bits per second, bps)
System Oscillator clock frequency
UBRRn
Contents of the UBRRnH and UBRRnL Registers, (0-4095)
16.4. 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 the
following figure. 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 the
following table. Note that changing the setting of any of these bits will corrupt all ongoing communication
for both the Receiver and Transmitter.
Table 16-2.ꢀ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 16-1.ꢀUCPHAn and UCPOLn data transfer timing diagrams.
UCPOL=0
UCPOL=1
XCK
XCK
Data setup (TXD)
Data sample (RXD)
Data setup (TXD)
Data sample (RXD)
XCK
XCK
Data setup (TXD)
Data sample (RXD)
Data setup (TXD)
Data sample (RXD)
16.5. Frame Formats
A serial frame for the MSPIM is defined to be one character of eight 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.
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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.
16.5.1. 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
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
{
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. */
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/* IMPORTANT: The Baud Rate must be set after the transmitter is enabled */
UBRRn = baud;
}
16.6. 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
USART_MSPIM_Transfer:
; Wait for empty transmit buffer
in r16, UCSRnA
sbrs r16, 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:
in r16, UCSRnA
sbrs r16, RXCn
rjmp USART_MSPIM_Wait_RXCn
; Get and return received data from buffer
in r16, UDRn
ret
C Code Example
{
/* Wait for empty transmit buffer */
while ( !( UCSRnA & (1<<UDREn)) );
/* Put data into buffer, sends the data */
UDRn = data;
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/* Wait for data to be received */
while ( !(UCSRnA & (1<<RXCn)) );
/* Get and return received data from buffer */
return UDRn;
}
16.6.1. 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.
16.6.2. 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.
16.7. AVR USART MSPIM vs. 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 the table below.
Table 16-3.ꢀComparison of USART in MSPIM mode and SPI pins
USART_MSPIM
TxDn
SPI
Comments
MOSI
MISO
SCK
SS
Master Out only
RxDn
Master In only
XCKn
(Functionally identical)
Not supported by USART in MSPIM
(N/A)
16.8. Register Description
Refer to the USART Register Description.
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17.
TC0 - 16-bit Timer/Counter0 with PWM
17.1. Overview
The 16-bit Timer/Counter unit allows accurate program execution timing (event management), wave
generation, and signal timing measurement.
A block diagram of the 16-bit Timer/Counter is shown below. 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
Register Description. For the actual placement of I/O pins, refer to the Pin Configurations description.
Related Links
Pin Configurations on page 12
17.2. 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
Independent interrupt Sources (TOV, OCFA, OCFB, and ICF)
17.3. Block Diagram
The Power Reduction TC0 bit in the Power Reduction Register (PRR0.PRTIM0) must be written to zero
to enable the TC0 module.
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Figure 17-1.ꢀ16-bit Timer/Counter Block Diagram
Count
Clear
TOVn
(Int.Req.)
Control Logic
Clock Select
Direction
clkTn
Edge
Detector
Tn
TOP
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
=
= 0
OCnA
(Int.Req.)
Waveform
Generation
OCnA
=
OCRnA
OCnB
(Int.Req.)
Fixed
TOP
Values
Waveform
Generation
OCnB
=
OCRnB
( From Analog
Comparator Ouput )
ICFn (Int.Req.)
Edge
Detector
Noise
Canceler
ICRn
ICPn
TCCRnA
TCCRnB
See the related links for actual pin placement.
17.4. Definitions
Many register and bit references in this section are written in general form:
•
•
n=0 represents the Timer/Counter number
x=A,B represents the Output Compare Unit A or B
However, when using the register or bit definitions in a program, the precise form must be used, i.e.,
TCNT0 for accessing Timer/Counter0 counter value.
The following definitions are used throughout the section:
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Table 17-1.ꢀDefinitions
Constant Description
BOTTOM The counter reaches the BOTTOM when it becomes zero (0x00 for 8-bit counters, or 0x0000
for 16-bit counters).
MAX
The counter reaches its Maximum when it becomes 0xF (decimal 15, for 8-bit counters) or
0xFF (decimal 255, for 16-bit counters).
TOP
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 MAX or the value stored in
the OCR0A Register. The assignment is dependent on the mode of operation.
17.5. Registers
The Timer/Counter (TCNT0), Output Compare Registers (OCRA/B), and Input Capture Register (ICR0)
are all 16-bit registers. Special procedures must be followed when accessing the 16-bit registers. These
procedures are described in section Accessing 16-bit Registers.
The Timer/Counter Control Registers (TCCR0A/B/C) are 8-bit registers and have no CPU access
restrictions. Interrupt requests (abbreviated to Int.Req. in the block diagram) 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/B) 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 (OC0A/B). See Output Compare Units. The
compare match event will also set the Compare Match Flag (OCF0A/B) 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 (ICP0) or on the Analog Comparator pins. 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 OCR0A Register, the ICR0 Register, or by a set of fixed values. When using OCR0A as TOP value in
a PWM mode, the OCR0A 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 ICR0 Register can be used as an alternative, freeing the OCR0A to be used as
PWM output.
Related Links
ICR0L and ICR0H on page 156
OCR0AL and OCR0AH on page 154
OCR0BL and OCR0BH on page 155
TCNT0L and TCNT0H on page 153
TCCR0A on page 147
TCCR0B on page 150
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TIFR0 on page 158
TIMSK0 on page 157
AC - Analog Comparator on page 160
17.6. Accessing 16-bit Timer/Counter Registers
The TCNT0, OCR0A/B, and ICR0 are 16-bit registers that can be accessed by the AVR CPU via the 8-bit
data bus. The 16-bit register must be accessed byte-wise, using two read or write operations. Each 16-bit
timer has a single 8-bit TEMP 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 that is currently stored in TEMP and the low byte being 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 TEMP register in the same clock cycle as
the low byte is read, and must be read subsequently.
Note:ꢀ To perform a 16-bit write operation, the low byte must be written before the high byte. For a 16-bit
read, the low byte must be read before the high byte.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCR0A/B 16-bit
registers does not involve using the temporary register.
16-bit Access
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 OCR0A/B and
ICR0 Registers. Note that when using C, the compiler handles the 16-bit access.
Assembly Code Example(1)
...
; Set TCNT0 to 0x01FF
ldi
ldi
out
out
r17,0x01
r16,0xFF
TCNT0H,r17
TCNT0L,r16
; Read TCNT0 into r17:r16
in
in
r16,TCNT0L
r17,TCNT0H
...
The assembly code example returns the TCNT0 value in the r17:r16 register pair.
C Code Example(1)
unsigned int i;
...
/* Set TCNT0 to 0x01FF */
TCNT0 = 0x1FF;
/* Read TCNT0 into i */
i = TCNT0;
...
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”.
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Atomic Read
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.
The following code examples show how to perform an atomic read of the TCNT0 Register contents. The
OCR0A/B or ICR0 Registers can be ready by using the same principle.
Assembly Code Example(1)
TIM16_ReadTCNT0:
; Save global interrupt flag
in
r18,SREG
; Disable interrupts
cli
; Read TCNT0 into r17:r16
in
in
r16,TCNT0L
r17,TCNT0H
; Restore global interrupt flag
out
ret
SREG,r18
The assembly code example returns the TCNT0 value in the r17:r16 register pair.
C Code Example(1)
unsigned int TIM16_ReadTCNT0( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNT0 into i */
i = TCNT0;
/* 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”.
Atomic Write
The following code examples show how to do an atomic write of the TCNT0 Register contents. Writing
any of the OCR0A/B or ICR0 Registers can be done by using the same principle.
Assembly Code Example(1)
TIM16_WriteTCNT0:
; Save global interrupt flag
in
r18,SREG
; Disable interrupts
cli
; Set TCNT0 to r17:r16
out
out
TCNT0H,r17
TCNT0L,r16
; Restore global interrupt flag
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out
ret
SREG,r18
The assembly code example requires that the r17:r16 register pair contains the value to
be written to TCNT0.
C Code Example(1)
void TIM16_WriteTCNT0( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT0 to i */
TCNT0 = 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”.
17.6.1. 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, the high
byte only needs to be written once. However, the same rule of atomic operation described previously also
applies in this case.
17.7. 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 bits in the Timer/Counter control
Register B (TCCR0B.CS[2:0]).
17.7.1. Internal Clock Source - Prescaler
The Timer/Counter can be clocked directly by the system clock (by setting the TCCR0B.CS0[2:0]=0x1).
This provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system clock
frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a clock source. The
prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or fCLK_I/O/1024.
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Figure 17-2.ꢀPrescaler for Timer/Counter0
clkI/O
Clear
PSR10
T0
Synchronization
clkT0
17.7.2. Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of the Timer/Counter,
and it is shared by Timer/Counter 0 (T0). Since the prescaler is not affected by the Timer/Counter’s clock
select, the state of the prescaler will have implications for situations where a prescaled clock is used. One
example of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler
(TCCR0B.CS0[2:0] = 2, 3, 4, or 5). The number of system clock cycles from when the timer is enabled to
the first count occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8,
64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execution.
However, care must be taken if the other Timer/Counter that shares the same prescaler also uses
prescaling. A prescaler reset will affect the prescaler period for all Timer/Counters it is connected to.
17.7.3. External Clock Source
An external clock source applied to the T0 pin can be used as Timer/Counter clock (clkT0). The T0 pin is
sampled once every system clock cycle by the pin synchronization logic. The synchronized (sampled)
signal is then passed through the edge detector. See also the block diagram of the T0 synchronization
and edge detector logic below. The registers are clocked at the positive edge of the internal system clock
(clkI/O). The latch is transparent in the high period of the internal system clock.
The edge detector generates one clkT0 pulse for each positive (CS0[2:0]=0x7) or negative (CS0[2:0]=0x6)
edge it detects.
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Figure 17-3.ꢀT0 Pin Sampling
Tn_sync
(To Clock
Tn
D
Q
D
Q
D
Q
Select Logic)
LE
clkI/O
Synchronization
Edge Detector
Note:ꢀ The “n” indicates the device number (n = 0 for Timer/Counter 0)
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles from an
edge has been applied to the T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when T0 has been stable for at least one system
clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
Each half period of the external clock applied must be longer than one system clock cycle to ensure
correct sampling. The external clock must be guaranteed to have less than half the system clock
frequency (fExtClk < fclk_I/O/2) given a 50% duty cycle. Since the edge detector uses sampling, the
maximum frequency of an external clock it can detect is half the sampling frequency (Nyquist sampling
theorem). However, due to variation of the system clock frequency and duty cycle caused by the
tolerances of the oscillator source (crystal, resonator, and capacitors), it is recommended that maximum
frequency of an external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
17.8. Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit, as shown
in the block diagram:
Figure 17-4.ꢀCounter Unit Block Diagram
DATA BUS(8-bit)
TOVn
(Int.Req.)
TEMP (8-bit)
Clock Select
Edge
Count
Tn
Detector
TCNTnH (8-bit)
TCNTnL (8-bit)
Clear
clkTn
Control Logic
Direction
TCNTn (16-bit Counter)
( From Prescaler )
TOP BOTTOM
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
Table 17-2.ꢀSignal description (internal signals)
Signal Name
Count
Description
Increment or decrement TCNT0 by 1.
Select between increment and decrement.
Clear TCNT0 (set all bits to zero).
Direction
Clear
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Signal Name
clkT0
Description
Timer/Counter clock.
TOP
Signalize that TCNT0 has reached maximum value.
Signalize that TCNT0 has reached minimum value (zero).
BOTTOM
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNT0H) containing the
upper eight bits of the counter, and Counter Low (TCNT0L) containing the lower eight bits. The TCNT0H
Register can only be accessed indirectly by the CPU. When the CPU does an access to the TCNT0H I/O
location, the CPU accesses the high byte temporary register (TEMP). The temporary register is updated
with the TCNT0H value when the TCNT0L is read, and TCNT0H is updated with the temporary register
value when TCNT0L 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.
Note:ꢀ That there are special cases when writing to the TCNT0 Register while the counter is counting will
give unpredictable results. These special cases are described in the sections where they are of
importance.
Depending on the selected mode of operation, the counter is cleared, incremented, or decremented at
each timer clock (clkT0). The clock clkT0 can be generated from an external or internal clock source, as
selected by the Clock Select bits in the Timer/Counter0 Control Register B (TCCR0B.CS[2:0]). When no
clock source is selected (CS[2:0]=0x0) the timer is stopped. However, the TCNT0 value can be accessed
by the CPU, independent of whether clkT0 is present or not. A CPU write overrides (i.e., has priority over)
all counter clear or count operations.
The counting sequence is determined by the setting of the Waveform Generation mode bits in the Timer/
Counter Control Registers A and B (TCCR0B.WGM0[3:2] and TCCR0A.WGM0[1:0]). There are close
connections between how the counter behaves (counts) and how waveforms are generated on the Output
Compare outputs OC0x. For more details about advanced counting sequences and waveform generation,
see Modes of Operation.
The Timer/Counter Overflow Flag in the TC0 Interrupt Flag Register (TIFR0.TOV) is set according to the
mode of operation selected by the WGM0[3:0] bits. TOV can be used for generating a CPU interrupt.
17.9. Input Capture Unit
The Timer/Counter0 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 ICP0 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 below. The elements of the block diagram that
are not directly a part of the Input Capture unit are gray shaded. The lower case “n” in register and bit
names indicates the Timer/Counter number.
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Figure 17-5.ꢀInput Capture Unit Block Diagram for TC0
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
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
When a change of the logic level (an event) occurs on the Input Capture pin (ICP0), or alternatively on the
Analog Comparator output (ACO), and this change confirms to the setting of the edge detector, a capture
will be triggered: the 16-bit value of the counter (TCNT0) is written to the Input Capture Register (ICR0).
The Input Capture Flag (ICF) is set at the same system clock cycle as the TCNT0 value is copied into the
ICR0 Register. If enabled (TIMSK0.ICIE=1), the Input Capture Flag generates an Input Capture interrupt.
The ICF0 Flag is automatically cleared when the interrupt is executed. Alternatively the ICF Flag can be
cleared by software by writing '1' to its I/O bit location.
Reading the 16-bit value in the Input Capture Register (ICR0) is done by first reading the low byte
(ICR0L) and then the high byte (ICR0H). When the low byte is read form ICR0L, the high byte is copied
into the high byte temporary register (TEMP). When the CPU reads the ICR0H I/O location it will access
the TEMP Register.
The ICR0 Register can only be written when using a Waveform Generation mode that utilizes the ICR0
Register for defining the counter’s TOP value. In these cases the Waveform Generation mode bits
(WGM0[3:0]) must be set before the TOP value can be written to the ICR0 Register. When writing the
ICR0 Register, the high byte must be written to the ICR0H I/O location before the low byte is written to
ICR0L.
See also Accessing 16-bit Timer/Counter Registers.
17.9.1. Input Capture Trigger Source
The main trigger source for the Input Capture unit is the Input Capture pin (ICP0). Timer/Counter0 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
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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 (ICP0) and the Analog Comparator output (ACO) inputs are sampled using the
same technique as for the T0 pin. 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. 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 ICR0 to define TOP.
An Input Capture can be triggered by software by controlling the port of the ICP0 pin.
Related Links
ACSRA on page 162
17.9.2. 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 bit in the Timer/Counter
Control Register B (TCCR0B.ICNC). When enabled, the noise canceler introduces an additional delay of
four system clock cycles between a change applied to the input and the update of the ICR0 Register. The
noise canceler uses the system clock and is therefore not affected by the prescaler.
17.9.3. 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 ICR0 Register before the next event occurs, the ICR0 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 ICR0 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 ICR0 Register has been
read. After a change of the edge, the Input Capture Flag (ICF) must be cleared by software (writing a
logical one to the I/O bit location). For measuring frequency only, the clearing of the ICF Flag is not
required (if an interrupt handler is used).
17.10. Output Compare Units
The 16-bit comparator continuously compares TCNT0 with the Output Compare Register (OCR0x). If
TCNT equals OCR0x the comparator signals a match. A match will set the Output Compare Flag
(TIFR0.OCFx) at the next timer clock cycle. If enabled (TIMSK0.OCIEx = 1), the Output Compare Flag
generates an Output Compare interrupt. The OCFx Flag is automatically cleared when the interrupt is
executed. Alternatively the OCFx 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 (WGM0[3:0]) bits and Compare Output mode (COM0x[1:0])
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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, see Modes of Operation.
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.
Below is a block diagram of the Output Compare unit. The elements of the block diagram that are not
directly a part of the Output Compare unit are gray shaded.
Figure 17-6.ꢀ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-bit Comparator )
OCFnx (Int.Req.)
TOP
OCnx
Waveform Generator
BOTTOM
WGMn[3:0]
COMnx[1:0]
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
The OCR0x 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 OCR0x 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.
When double buffering is enabled, the CPU has access to the OCR0x Buffer Register. When double
buffering is disabled, the CPU will access the OCR0x directly.
The content of the OCR0x (Buffer or Compare) Register is only changed by a write operation (the Timer/
Counter does not update this register automatically as the TCNT0 and ICR0 Register). Therefore OCR0x
is not read via the high byte temporary register (TEMP). However, it is good practice to read the low byte
first as when accessing other 16-bit registers. Writing the OCR0x Registers must be done via the TEMP
Register since the compare of all 16 bits is done continuously. The high byte (OCR0xH) 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 (OCR0xL) is written to the lower eight bits, the high byte will be
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copied into the upper 8-bits of either the OCR0x buffer or OCR0x Compare Register in the same system
clock cycle.
For more information of how to access the 16-bit registers refer to Accessing 16-bit Timer/Counter
Registers.
17.10.1. Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a
'1' to the Force Output Compare (TCCR0C.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 TCCR0A.COM0x[1:0] bits define whether the OC0x pin is set, cleared or toggled).
17.10.2. 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.
17.10.3. 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 TCCR0A.COM0x[1:0] bits are not double buffered together with the compare value.
Changing the TCCR0A.COM0x[1:0] bits will take effect immediately.
17.11. Compare Match Output Unit
The Compare Output mode bits in the Timer/Counter Control Register A (TCCR0A.COM0x) have two
functions:
•
The Waveform Generator uses the COM0x bits for defining the Output Compare (OC0x) register
state at the next compare match.
•
The COM0x bits control the OC0x pin output source
The figure below shows a simplified schematic of the logic affected by COM0x. 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
that are affected by the COM0x bits are shown, namely PORT and DDR.
On system reset the OC0x Register is reset to 0x00.
Note:ꢀ 'OC0x state' is always referring to internal OC0x registers, not the OC0x pin.
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Figure 17-7.ꢀCompare Match Output Unit, Schematic
COMnx[1]
Waveform
Generator
COMnx[0]
FOCnx
D
Q
1
0
OCnx
Pin
OCnx
D
Q
PORT
D
Q
DDR
clkI/O
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform Generator
if either of the COM0x[1:0] bits are set. However, the OC0x pin direction (input or output) is still controlled
by the Data Direction Register (DDR) for the port pin. In the Data Direction Register, the 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 register state before the
output is enabled. Some TCCR0A.COM0x[1:0] bit settings are reserved for certain modes of operation.
The TCCR0A.COM0x[1:0] bits have no effect on the Input Capture unit.
17.11.1. Compare Output Mode and Waveform Generation
The Waveform Generator uses the TCCR0A.COM0x[1:0] bits differently in Normal, CTC, and PWM
modes. For all modes, setting the TCCR0A.COM0x[1:0]=0x0 tells the Waveform Generator that no action
on the OC0x Register is to be performed on the next compare match. Refer also to the descriptions of the
output modes.
A change of the TCCR0A.COM0x[1:0] 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
TCCR0C.FOC0x strobe bits.
17.12. 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 (WGM0[3:0]) and Compare Output mode
(TCCR0A.COM0x[1:0]) bits. The Compare Output mode bits do not affect the counting sequence, while
the Waveform Generation mode bits do. The TCCR0A.COM0x[1:0] bits control whether the PWM output
generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the
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TCCR0A.COM0x[1:0] bits control whether the output should be set, cleared, or toggle at a compare
match.
17.12.1. Normal Mode
The simplest mode of operation is the Normal mode (TCCR0A.WGM0[3:0]=0x0). 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
BOTTOM=0x0000. In normal operation the Timer/Counter Overflow Flag (TIFR0.TOV) will be set in the
same timer clock cycle as the TCNT0 becomes zero. In this case, the TOV Flag in behaves like a 17th
bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt that
automatically clears the TOV 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.
17.12.2. Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC modes (mode 4 or 12, WGM0[3:0]=0x4 or 0xC), the OCR0A or ICR0
registers are used to manipulate the counter resolution: the counter is cleared to ZERO when the counter
value (TCNT0) matches either the OCR0A (if WGM0[3:0]=0x4) or the ICR0 (WGM0[3:0]=0xC). The
OCR0A or ICR0 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 below. The counter value (TCNT0) increases until a
compare match occurs with either OCR0A or ICR0, and then TCNT0 is cleared.
Figure 17-8.ꢀCTC Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnA
(Toggle)
(COMnA[1:0] = 0x1)
1
2
3
4
Period
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
An interrupt can be generated at each time the counter value reaches the TOP value by either using the
OCF0A or ICF0 Flag, depending on the actual CTC mode. If the interrupt is enabled, the interrupt handler
routine can be used for updating the TOP value.
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Note:ꢀ Changing TOP to a value close to BOTTOM while the counter is running must be done with care,
since the CTC mode does not provide double buffering. 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 count to its
maximum value (0xFF for a 8-bit counter, 0xFFFF for a 16-bit counter) and wrap around starting at 0x00
before the compare match will occur.
In many cases this feature is not desirable. An alternative will then be to use the Fast PWM mode using
OCR0A for defining TOP (WGM0[3:0]=0xF), since the OCR0A then will be double buffered.
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 (COM0A[1:0]=0x1). The
OC0A value will not be visible on the port pin unless the data direction for the pin is set to output
(DDR_OC0A=1). The waveform generated will have a maximum frequency of fOC0A = fclk_I/O/2 when
OCR0A is set to ZERO (0x0000). The waveform frequency is defined by the following equation:
ꢀ
clk_I/O
ꢀ
=
OCnA
2 ⋅ ꢏ ⋅ 1 + OCRnA
Note:ꢀ
•
The “n” indicates the device number (n = 0 for Timer/Counter 0), and the “x” indicates Output
Compare unit (A/B).
•
N represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the Timer Counter TOV Flag is set in the same timer clock cycle
that the counter counts from MAX to 0x0000.
17.12.3. Fast PWM Mode
The Fast Pulse Width Modulation or Fast PWM modes (modes 5, 6, 7, 14,and 15, WGM0[3:0]= 0x5, 0x6,
0x7, 0xE, 0xF) provide 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 (OC0x) is cleared on the compare match
between TCNT0 and OCR0x, 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 ICR0 or OCR0A.
The minimum resolution allowed is 2-bit (ICR0 or OCR0A register set to 0x0003), and the maximum
resolution is 16-bit (ICR0 or OCR0A registers set to MAX). The PWM resolution in bits can be calculated
by using the following equation:
log TOP+1
ꢇ
=
FPWM
log 2
In Fast PWM mode the counter is incremented until the counter value matches either one of the fixed
values 0x00FF, 0x01FF, or 0x03FF (WGM0[3:0] = 0x5, 0x6, or 0x7), the value in ICR0 (WGM0[3:0]=0xE),
or the value in OCR0A (WGM0[3:0]=0xF). The counter is then cleared at the following timer clock cycle.
The timing diagram for the Fast PWM mode using OCR0A or ICR0 to define TOP is shown below. 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 lines on the TCNT0
slopes mark compare matches between OCR0x and TCNT0. The OC0x Interrupt Flag will be set when a
compare match occurs.
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Figure 17-9.ꢀ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
(COMnx[1:0] = 0x2)
(COMnx[1:0] = 0x3)
OCnx
OCnx
1
2
3
4
5
6
7
8
Period
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. In addition, when
either OCR0A or ICR0 is used for defining the TOP value, the OC0A or ICF0 Flag is set at the same timer
clock cycle TOV0 is set. 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 TCNT0 and the OCR0x. Note that when using fixed TOP
values the unused bits are masked to zero when any of the OCR0x Registers are written.
The procedure for updating ICR0 differs from updating OCR0A when used for defining the TOP value.
The ICR0 Register is not double buffered. This means that if ICR0 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 ICR0 value written is
lower than the current value of TCNT0. As result, 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 OCR0A Register however, is double buffered. This
feature allows the OCR0A I/O location to be written anytime. When the OCR0A I/O location is written the
value written will be put into the OCR0A Buffer Register. The OCR0A Compare Register will then be
updated with the value in the Buffer Register at the next timer clock cycle the TCNT0 matches TOP. The
update is done at the same timer clock cycle as the TCNT0 is cleared and the TOV0 Flag is set.
Using the ICR0 Register for defining TOP works well when using fixed TOP values. By using ICR0, the
OCR0A Register is free to be used for generating a PWM output on OC0A. However, if the base PWM
frequency is actively changed (by changing the TOP value), using the OCR0A as TOP is clearly a better
choice due to its double buffer feature.
In Fast PWM mode, the compare units allow generation of PWM waveforms on the OC0x pins. Writing
the COM0x[1:0] bits to 0x2 will produce an inverted PWM and a non-inverted PWM output can be
generated by writing the COM0x[1:0] to 0x3. The actual OC0x value will only be visible on the port pin if
the data direction for the port pin is set as output (DDR_OC0x). The PWM waveform is generated by
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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:
ꢀ
clk_I/O
ꢀ
=
OCnxPWM
ꢏ ⋅ 1 + TOP
Note:ꢀ
•
The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
•
N represents the prescale divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR0x registers represents special cases when generating a PWM waveform
output in the Fast PWM mode. If the OCR0x is set equal to BOTTOM (0x0000) the output will be a narrow
spike for each TOP+1 timer clock cycle. Setting the OCR0x equal to TOP will result in a constant high or
low output (depending on the polarity of the output which is controlled by COM0x[1:0]).
A frequency waveform output with 50% duty cycle can be achieved in Fast PWM mode by selecting
OC0A to toggle its logical level on each compare match (COM0A[1:0]=0x1). This applies only if OCR0A is
used to define the TOP value (WGM0[3:0]=0xF). The waveform generated will have a maximum
frequency of fOC0A = fclk_I/O/2 when OCR0A is set to zero (0x0000). 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.
17.12.4. Phase Correct PWM Mode
The Phase Correct Pulse Width Modulation or Phase Correct PWM modes (WGM0[3:0]= 0x1, 0x2, 0x3,
0xA, and 0xB) provide 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 (OC0x) is cleared on the
compare match between TCNT0 and OCR0x while up-counting, 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.
The PWM resolution for the Phase Correct PWM mode can be fixed to 8-, 9-, or 10-bit, or defined by
either ICR0 or OCR0A. The minimum resolution allowed is 2-bit (ICR0 or OCR0A set to 0x0003), and the
maximum resolution is 16-bit (ICR0 or OCR0A set to MAX). The PWM resolution in bits can be calculated
by using the following equation:
log TOP+1
ꢇ
=
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 (WGM0[3:0]= 0x1, 0x2, or 0x3), the value in ICR0
(WGM0[3:0]=0xA), or the value in OCR0A (WGM0[3:0]=0xB). The counter has then reached the TOP and
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 below, using OCR0A or ICR0 to define TOP. 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 lines on the TCNT0
slopes mark compare matches between OCR0x and TCNT0. The OC0x Interrupt Flag will be set when a
compare match occurs.
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Figure 17-10.ꢀ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
(COMnx[1:0]] = 0x2)
OCnx
OCnx
(COMnx[1:0] = 0x3)
1
2
3
4
Period
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOTTOM. When either
OCR0A or ICR0 is used for defining the TOP value, the OC0A or ICF0 Flag is set accordingly at the same
timer clock cycle as the OCR0x 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 TCNT0 and the OCR0x. Note that when using fixed TOP
values, the unused bits are masked to zero when any of the OCR0x registers is written. As illustrated by
the third period in the timing diagram, 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 OCR0x Register. Since the OCR0x 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 OC0x pins.
Writing COM0x[1:0] bits to 0x2 will produce a non-inverted PWM. An inverted PWM output can be
generated by writing the COM0x[1:0] to 0x3. The actual OC0x value will only be visible on the port pin if
the data direction for the port pin is set as output (DDR_OC0x). The PWM waveform is generated by
setting (or clearing) the OC0x Register at the compare match between OCR0x and TCNT0 when the
counter increments, and clearing (or setting) the OC0x Register at compare match between OCR0x and
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TCNT0 when the counter decrements. The PWM frequency for the output when using Phase Correct
PWM can be calculated by the following equation:
ꢀ
clk_I/O
ꢀ
=
OCnxPCPWM
2 ⋅ ꢏ ⋅ TOP
N represents the prescale divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR0x Register represent special cases when generating a PWM waveform
output in the Phase Correct PWM mode. If the OCR0x 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 OCR0A is used to define the TOP
value (WGM0[3:0]=0xB) and COM0A[1:0]=0x1, the OC0A output will toggle with a 50% duty cycle.
17.12.5. Phase and Frequency Correct PWM Mode
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM mode
(WGM0[3:0] = 0x8 or 0x9) 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 (OC0x) is
cleared on the compare match between TCNT0 and OCR0x while up-counting, and set on the compare
match while down-counting. 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 OCR0x Register is updated by the OCR0x Buffer Register, (see Figure 17-10 and the Timing
Diagram below).
The PWM resolution for the phase and frequency correct PWM mode can be defined by either ICR0 or
OCR0A. The minimum resolution allowed is 2-bit (ICR0 or OCR0A set to 0x0003), and the maximum
resolution is 16-bit (ICR0 or OCR0A set to MAX). The PWM resolution in bits can be calculated using the
following equation:
log TOP+1
ꢇ
=
PFCPWM
log 2
In phase and frequency correct PWM mode the counter is incremented until the counter value matches
either the value in ICR0 (WGM0[3:0]=0x8), or the value in OCR0A (WGM0[3:0]=0x9). The counter has
then reached the TOP and changes the count direction. The TCNT0 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
below. The figure shows phase and frequency correct PWM mode when OCR0A or ICR0 is used to
define TOP. 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. The OC0x Interrupt Flag
will be set when a compare match occurs.
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Figure 17-11.ꢀPhase and Frequency Correct PWM Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
OCRnx/TOP Updateand
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
(COMnx[1:0] = 0x2)
(COMnx[1:0] = 0x3)
OCnx
OCnx
1
2
3
4
Period
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
The Timer/Counter Overflow Flag (TOV0) is set at the same timer clock cycle as the OCR0x Registers
are updated with the double buffer value (at BOTTOM). When either OCR0A or ICR0 is used for defining
the TOP value, the OC0A or ICF0 Flag set when TCNT0 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 TCNT0 and the OCR0x.
As shown in the timing diagram above, the output generated is, in contrast to the phase correct mode,
symmetrical in all periods. Since the OCR0x 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 ICR0 Register for defining TOP works well when using fixed TOP values. By using ICR0, the
OCR0A Register is free to be used for generating a PWM output on OC0A. However, if the base PWM
frequency is actively changed by changing the TOP value, using the OCR0A 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 OC0x pins. Setting the COM0x[1:0] bits to 0x2 will produce a non-inverted PWM and an inverted
PWM output can be generated by setting the COM0x[1:0] to 0x3 (See description of TCCRA.COM0x).
The actual OC0x value will only be visible on the port pin if the data direction for the port pin is set as
output (DDR_OC0x). The PWM waveform is generated by setting (or clearing) the OC0x Register at the
compare match between OCR0x and TCNT0 when the counter increments, and clearing (or setting) the
OC0x Register at compare match between OCR0x and TCNT0 when the counter decrements. The PWM
frequency for the output when using phase and frequency correct PWM can be calculated by the
following equation:
ꢀ
clk_I/O
ꢀ
=
OCnxPFCPWM
2 ⋅ ꢏ ⋅ TOP
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Note:ꢀ
•
The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
•
N represents the prescale divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR0x Register represents special cases when generating a PWM waveform
output in the phase correct PWM mode. If the OCR0x 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 OCR0A is used to define the TOP value
(WGM0[3:0]=0x9) and COM0A[1:0]=0x1, the OC0A output will toggle with a 50% duty cycle.
17.13. 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, and
when the OCR0x Register is updated with the OCR0x buffer value (only for modes utilizing double
buffering). The first figure shows a timing diagram for the setting of OCF0x.
Figure 17-12.ꢀTimer/Counter Timing Diagram, Setting of OCF0x, no Prescaling
clkI/O
clkTn
(clkI/O/1)
TCNTn
OCRnx
OCFnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
The next figure shows the same timing data, but with the prescaler enabled.
Figure 17-13.ꢀTimer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
OCRnx
OCFnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
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Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
The next figure shows the count sequence close to TOP in various modes. When using phase and
frequency correct PWM mode the OCR0x 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 TOV0 Flag at BOTTOM.
Figure 17-14.ꢀ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)
New OCRnx Value
Old OCRnx Value
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
The next figure shows the same timing data, but with the prescaler enabled.
Figure 17-15.ꢀTimer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clk
I/O
clk
Tn
(clk /8)
I/O
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
Note:ꢀ The “n” in the register and bit names indicates the device number (n = 0 for Timer/Counter 0), and
the “x” indicates Output Compare unit (A/B).
17.14. Register Description
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17.14.1. Timer/Counter0 Control Register A
Name:ꢀ TCCR0A
Offset:ꢀ 0x2E
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
COM0A1
R/W
6
COM0A0
R/W
5
COM0B1
R/W
4
COM0B0
R/W
3
2
1
WGM01
R/W
0
0
WGM00
R/W
0
Access
Reset
0
0
0
0
Bits 7:6 – COM0An:ꢀCompare Output Mode for Channel A [n = 1:0]
Bits 5:4 – COM0Bn:ꢀCompare Output Mode for Channel B [n = 1:0]
The COM0A[1:0] and COM0B[1:0] control the Output Compare pins (OC0A and OC0B respectively)
behavior. If one or both of the COM0A[1:0] bits are written to one, the OC0A output overrides the normal
port functionality of the I/O pin it is connected to. If one or both of the COM0B[1:0] bit are written to one,
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 OC0A or OC0B pin must be set in order
to enable the output driver.
When the OC0A or OC0B is connected to the pin, the function of the COM0x[1:0] bits is dependent of the
WGM0[3:0] bits setting. The table below shows the COM0x[1:0] bit functionality when the WGM0[3:0] bits
are set to a Normal or a CTC mode (non-PWM).
Table 17-3.ꢀCompare Output Mode, non-PWM
COM0A1/COM0B1 COM0A0/COM0B0 Description
0
0
1
0
1
0
Normal port operation, OC0A/OC0B disconnected.
Toggle OC0A/OC0B on Compare Match.
Clear OC0A/OC0B on Compare Match (Set output to low
level).
1
1
Set OC0A/OC0B on Compare Match (Set output to high
level).
The table below shows the COM0x[1:0] bit functionality when the WGM0[3:0] bits are set to the fast PWM
mode.
Table 17-4.ꢀCompare Output Mode, Fast PWM
COM0A1/
COM0B1
COM0A0/
COM0B0
Description
0
0
0
1
Normal port operation, OC0A/OC0B disconnected.
WGM0[3:0]=0: Normal port operation, OC0A/OC0B
disconnected
WGM0[3:0]=1: Toggle OC0A on compare match, OC0B reserved
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COM0A1/
COM0B1
COM0A0/
COM0B0
Description
1(1)
0
Clear OC0A/OC0B on Compare Match, set OC0A/OC0B at
BOTTOM (non-inverting mode)
1(1)
1
Set OC0A/OC0B on Compare Match, clear OC0A/OC0B at
BOTTOM (inverting mode)
Note:ꢀ
1. A special case occurs when OCR0A/OCR0B equals TOP and COM0A1/COM0B1 is set. In this
case the compare match is ignored, but the set or clear is done at BOTTOM. Refer to Fast PWM
Mode for details.
The table below shows the COM0x[1:0] bit functionality when the WGM0[3:0] bits are set to the phase
correct or the phase and frequency correct, PWM mode.
Table 17-5.ꢀCompare Output Mode, Phase Correct and Phase and Frequency Correct PWM
COM0A1/
COM0B1
COM0A0/
COM0B0
Description
0
0
0
1
Normal port operation, OC0A/OC0B disconnected.
WGM0[3:0]=0: Normal port operation, OC0A/OC0B disconnected
WGM0[3:0]=1: Toggle OC0A on compare match, OC0B reserved
1(1)
1(1)
0
1
Clear OC0A/OC0B on Compare Match when up-counting. Set
OC0A/OC0B on Compare Match when down-counting.
Set OC0A/OC0B on Compare Match when up-counting. Clear
OC0A/OC0B on Compare Match when down-counting.
Note:ꢀ
1. A special case occurs when OCR0A/OCR0B equals TOP and COM0A1/COM0B1 is set. Refer to
Phase Correct PWM Mode for details.
Bits 1:0 – WGM0n:ꢀWaveform Generation Mode [n = 1:0]
Combined with the WGM0[3:2] bits 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. 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 Modes of Operation).
Table 17-6.ꢀWaveform Generation Mode Bit Description
Mode
WGM0[3:0]
0000
Timer/Counter Mode of Operation
Normal
TOP
Update of OCR0x at
TOV0 Flag Set on
MAX
0
1
2
3
4
5
6
0xFFFF
0x00FF
0x01FF
0x03FF
OCR0A
0x00FF
0x01FF
Immediate
TOP
0001
PWM, Phase Correct, 8-bit
PWM, Phase Correct, 9-bit
PWM, Phase Correct, 10-bit
CTC (Clear Timer on Compare)
Fast PWM, 8-bit
BOTTOM
BOTTOM
BOTTOM
MAX
0010
TOP
0011
TOP
0100
Immediate
TOP
0101
TOP
0110
Fast PWM, 9-bit
TOP
TOP
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Mode
7
WGM0[3:0]
0111
Timer/Counter Mode of Operation
Fast PWM, 10-bit
TOP
0x03FF
ICR0
Update of OCR0x at
TOV0 Flag Set on
TOP
TOP
BOTTOM
BOTTOM
TOP
8
1000
PWM, Phase and Frequency Correct
PWM, Phase and Frequency Correct
PWM, Phase Correct
PWM, Phase Correct
CTC (Clear Timer on Compare)
Reserved
BOTTOM
BOTTOM
BOTTOM
BOTTOM
MAX
9
1001
OCR0A
ICR0
10
11
12
13
14
15
1010
1011
OCR0A
ICR0
TOP
1100
Immediate
-
1101
-
-
1110
Fast PWM
ICR0
TOP
TOP
1111
Fast PWM
OCR0A
TOP
TOP
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17.14.2. Timer/Counter0 Control Register B
Name:ꢀ TCCR0B
Offset:ꢀ 0x2D
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
ICNC0
R/W
0
6
ICES0
R/W
0
5
4
WGM03
R/W
0
3
WGM02
R/W
0
2
1
CS0[2:0]
R/W
0
Access
Reset
R/W
0
R/W
0
0
Bit 7 – ICNC0:ꢀ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 (ICP0) is filtered. The filter function requires four successive equal
valued samples of the ICP0 pin for changing its output. The Input Capture is therefore delayed by four
Oscillator cycles when the noise canceler is enabled.
Bit 6 – ICES0:ꢀInput Capture Edge Select
This bit selects which edge on the Input Capture pin (ICP0) that is used to trigger a capture event. When
the ICES0 bit is written to zero, a falling (negative) edge is used as trigger, and when the ICES0 bit is
written to one, a rising (positive) edge will trigger the capture.
When a capture is triggered according to the ICES0 setting, the counter value is copied into the Input
Capture Register (ICR0). The event will also set the Input Capture Flag (ICF0), and this can be used to
cause an Input Capture Interrupt, if this interrupt is enabled.
When the ICR0 is used as TOP value (see description of the WGM0[3:0] bits located in the TCCR0A and
the TCCR0B Register), the ICP0 is disconnected and consequently the Input Capture function is
disabled.
Bit 4 – WGM03:ꢀWaveform Generation Mode
Refer to TCCR0A.
Bit 3 – WGM02:ꢀWaveform Generation Mode
Refer to TCCR0A.
Bits 2:0 – CS0[2:0]:ꢀClock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter. Refer to Figure
17-12 and Figure 17-13.
Table 17-7.ꢀClock Select Bit Description
CA0[2]
CA0[1]
CS0[0] Description
0
0
0
0
1
0
0
1
1
0
0
1
0
1
0
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)
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CA0[2]
CA0[1]
CS0[0] Description
1
1
1
0
1
1
1
0
1
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/Counter 0, 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.
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17.14.3. Timer/Counter0 Control Register C
Name:ꢀ TCCR0C
Offset:ꢀ 0x2C
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
FOC0A
R/W
0
6
FOC0B
R/W
0
5
4
3
2
1
0
Access
Reset
Bit 7 – FOC0A:ꢀForce Output Compare for Channel A
Bit 6 – FOC0B:ꢀForce Output Compare for Channel B
The FOC0A/FOC0B bits are only active when the WGM0[3:0] bits specifies a non-PWM mode. When
writing a logical one to the FOC0A/FOC0B bit, an immediate compare match is forced on the Waveform
Generation unit. The OC0A/OC0B output is changed according to its COM0x[1:0] bits setting. Note that
the FOC0A/FOC0B bits are implemented as strobes. Therefore it is the value present in the COM0x[1:0]
bits that determine the effect of the forced compare.
A FOC0A/FOC0B strobe will not generate any interrupt nor will it clear the timer in Clear Timer on
Compare match (CTC) mode using OCR0A as TOP. The FOC0A/FOC0B bits are always read as zero.
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17.14.4. Timer/Counter 0 Low and High byte
The TCNT0L and TCNT0H register pair represents the 16-bit value, TCNT0.The low byte [7:0] (suffix L) is
accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset + 0x01. For
more details on reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
Name:ꢀ TCNT0L and TCNT0H
Offset:ꢀ 0x28
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
15
14
13
12
11
10
9
8
TCNT0[15:8]
Access
Reset
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
6
5
4
3
2
1
0
TCNT0[7:0]
Access
Reset
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 15:0 – TCNT0[15:0]:ꢀTimer/Counter 0
TCNT0H and TCNT0L are combined into TCNT0.
Modifying the counter (TCNT0) while the counter is running introduces a risk of missing a compare match
between TCNT0 and one of the OCR0x Registers.
Writing to the TCNT0 Register blocks (removes) the compare match on the following timer clock for all
compare units.
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17.14.5. Output Comparte Register A 0 Low and High byte
The OCR0AL and OCR0AH register pair represents the 16-bit value, OCR0A.The low byte [7:0] (suffix L)
is accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset + 0x01. For
more details on reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
Name:ꢀ OCR0AL and OCR0AH
Offset:ꢀ 0x26
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
15
14
13
12
11
10
9
8
OCR0A[15:8]
Access
Reset
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
6
5
4
3
2
1
0
OCR0A[7:0]
Access
Reset
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 15:0 – OCR0A[15:0]:ꢀOutput Compare 0 A
OCR0AH and OCR0AL are combined into OCR0A.
The Output Compare Registers contain a 16-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 OC0x pin.
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17.14.6. Output Comparte Register B 0 Low and High byte
The OCR0BL and OCR0BH register pair represents the 16-bit value, OCR0B.The low byte [7:0] (suffix L)
is accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset + 0x01. For
more details on reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
Name:ꢀ OCR0BL and OCR0BH
Offset:ꢀ 0x24
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
15
14
13
12
11
10
9
8
OCR0B[15:8]
Access
Reset
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
6
5
4
3
2
1
0
OCR0B[7:0]
Access
Reset
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 15:0 – OCR0B[15:0]:ꢀOutput Compare 0 B
OCR0BH and OCR0BL are combined into OCR0B.
The Output Compare Registers contain a 16-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 OC0x pin.
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17.14.7. Input Capture Register 0 Low and High byte
The ICR0L and ICR0H register pair represents the 16-bit value, ICR0.The low byte [7:0] (suffix L) is
accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset + 0x01. For
more details on reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
Name:ꢀ ICR0L and ICR0H
Offset:ꢀ 0x22
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
15
14
13
12
11
10
9
8
ICR0[15:8]
ICR0[7:0]
Access
Reset
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
6
5
4
3
2
1
0
Access
Reset
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 15:0 – ICR0[15:0]:ꢀInput Capture 0
ICR0H and ICR0L are combined into ICR0.
The Input Capture is updated with the counter (TCNT0) value each time an event occurs on the ICP0 pin
(or optionally on the Analog Comparator output for Timer/Counter0). The Input Capture can be used for
defining the counter TOP value.
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17.14.8. Timer/Counter0 Interrupt Mask Register
Name:ꢀ TIMSK0
Offset:ꢀ 0x2B
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
ICIE0
R/W
0
4
3
2
OCIE0B
R/W
0
1
OCIE0A
R/W
0
0
TOIE0
R/W
0
Access
Reset
Bit 5 – ICIE0:ꢀTimer/Counter0, 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/Counter0 Input Capture interrupt is enabled. The corresponding Interrupt Vector is executed when
the ICF0 Flag, located in TIFR0, is set.
Bit 2 – OCIE0B:ꢀTimer/Counter0, 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/Counter 0 Output Compare B Match interrupt is enabled. The corresponding Interrupt Vector is
executed when the OCF0B Flag, located in TIFR0, is set.
Bit 1 – OCIE0A:ꢀTimer/Counter0, 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/Counter0 Output Compare A Match interrupt is enabled. The corresponding Interrupt Vector is
executed when the OCF0A Flag, located in TIFR0, is set.
Bit 0 – TOIE0:ꢀTimer/Counter0, 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/Counter0 Overflow interrupt is enabled. The corresponding Interrupt Vector is executed when the
TOV0 Flag, located in TIFR0, is set.
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17.14.9. Timer/Counter0 Interrupt Flag Register
Name:ꢀ TIFR0
Offset:ꢀ 0x2A
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
6
5
4
3
2
OCF0B
R/W
0
1
OCF0A
R/W
0
0
TOV0
R/W
0
ICF0
R/W
0
Access
Reset
Bit 5 – ICF0:ꢀTimer/Counter0, Input Capture Flag
This flag is set when a capture event occurs on the ICP0 pin. When the Input Capture Register (ICR0) is
set by the WGM0[3:0] to be used as the TOP value, the ICF0 Flag is set when the counter reaches the
TOP value.
ICF0 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively, ICF0 can
be cleared by writing a logic one to its bit location.
Bit 2 – OCF0B:ꢀTimer/Counter0, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT0) value matches the Output Compare
Register B (OCR0B).
Note that a Forced Output Compare (FOC0B) strobe will not set the OCF0B Flag.
OCF0B is automatically cleared when the Output Compare Match B Interrupt Vector is executed.
Alternatively, OCF0B can be cleared by writing a logic one to its bit location.
Bit 1 – OCF0A:ꢀTimer/Counter0, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT0) value matches the Output Compare
Register A (OCR0A).
Note that a Forced Output Compare (FOC0A) strobe will not set the OCF0A Flag.
OCF0A is automatically cleared when the Output Compare Match A Interrupt Vector is executed.
Alternatively, OCF0A can be cleared by writing a logic one to its bit location.
Bit 0 – TOV0:ꢀTimer/Counter0, Overflow Flag
The setting of this flag is dependent of the WGM0[3:0] bits setting. In Normal and CTC modes, the TOV0
Flag is set when the timer overflows. Refer to Table 17-6 for the TOV0 Flag behavior when using another
WGM0[3:0] bit setting.
TOV0 is automatically cleared when the Timer/Counter0 Overflow Interrupt Vector is executed.
Alternatively, TOV0 can be cleared by writing a logic one to its bit location.
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17.14.10. General Timer/Counter Control Register
Name:ꢀ GTCCR
Offset:ꢀ 0x2F
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
REMAP
R/W
0
0
TSM
R/W
0
PSR
R/W
0
Access
Reset
Bit 7 – TSM:ꢀTimer/Counter Synchronization Mode
Writing the TSM bit to '1' activates the Timer/Counter Synchronization mode. In this mode, the value that
is written to the PSR bit is kept, hence keeping the Prescaler Reset signal asserted. This ensures that the
Timer/Counter is halted and can be configured without the risk of advancing during configuration. When
the TSM bit is written to '0', the PSR bit is cleared by hardware, and the Timer/Counter start counting.
Bit 1 – REMAP
This bit controls how the TIMER pins are mapped to pins as shown in the table:
REMAP
TO_CLK
PA0
OC0B
PA1
OC0A
PB1
ICP0
PB2
PA4
NOTE
0
1
DEFAULT
REMAPPED
PB3
PA5
PA3
Bit 0 – PSR:ꢀPrescaler 0 Reset Timer/Counter 0
When this bit is one, the Timer/Counter0 prescaler will be Reset. This bit is normally cleared immediately
by hardware, except if the TSM bit is set.
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18.
AC - Analog Comparator
18.1. 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.
18.2. Features
•
Flexible Input Selection:
–
–
Internal Voltage Reference
Two Pins Selectable for Positive or Negative Inputs
•
Interrupt Generation on:
–
–
–
Output Toggle
Falling Output Edge
Rising Output Edge
18.3. Block Diagram
Only one Internal reference (1.1V – Bandgap) will be connected to the positive input of the AC. For using
Bandgap reference voltage as positive input to AC , it is advisable that Bandgap reference is first enabled
by writing '1' to ACSRA.ACBG and then selected by writing '1' to ACSRB.ACPMUX . The output of
comparator 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 below.
The Power Reduction ADC bit in the Power Reduction Register (PRR.PRADC) must be written to '0' in
order to be able to use the ADC input MUX.
Figure 18-1.ꢀAnalog Comparator Block Diagram
VCC
1.1V Bandgap
reference voltage
ACD
ACIE
ANALOG
COMPARATOR
IRQ
AIN0
INTERRUPT
SELECT
ACBG
[AC BG ENABLE]
AIN1
ACI
ACIC
To T/C Capture
Trigger MUX
ACIS1
ACIS0
ACPMUX
ACO
ACO TO PAD
AC OUTPUT ENABLE
Note:ꢀ Refer to the Pin Configuration and the I/O Ports description for Analog Comparator pin placement.
Related Links
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Pin Configurations on page 12
18.4. Register Description
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18.4.1. Analog Comparator Control and Status Register
Name:ꢀ ACSRA
Offset:ꢀ 0x1F
Reset:ꢀ
Property:
ꢀ
0
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
ACD
R/W
0
Access
Reset
0
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 ENABLE
When this bit is set, 1.1V bandgap reference voltage is enabled. When ACPMUX bit is also set, bandgap
reference voltage is applied to the positive input of analog comparator. It is advised that bandgap
reference is first enabled by writing one to ACBG bit and then selected by writing one to ACPMUX bit to
allow the stabilization of voltage.
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.
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/Counter0 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/
Counter0 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/Counter0
Input Capture interrupt, the ICIE1 bit in the Timer Interrupt Mask Register (TIMSK0) must be set.
Bits 1:0 – ACISn:ꢀAnalog Comparator Interrupt Mode Select [n = 1:0]
These bits determine which comparator events that trigger the Analog Comparator interrupt.
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Table 18-1.ꢀACIS[1:0] 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.
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18.4.2. Analog Comparator Control and Status Register 0
Name:ꢀ ACSRB
Offset:ꢀ 0x1E
Reset:ꢀ 0x00
Property:
ꢀ
Bit
7
6
5
4
3
2
1
ACOE
R/W
0
0
ACPMUX
R/W
Access
Reset
0
Bit 1 – ACOE:ꢀAnalog Comparator Output Enable
When this bit is set, the analog comparator output is connected to the ACO pin.
Bit 0 – ACPMUX:ꢀAnalog Comparator Positive Input Multiplexer
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 the 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 a wrong value.
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18.4.3. Digital Input Disable Register 0
When the respective bits are written to 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 ADC[7:0] 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.
Name:ꢀ DIDR0
Offset:ꢀ 0x17
Reset:ꢀ 0x00
Property: -
ꢀ
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
Access
Reset
Bits 0, 1, 2, 3, 4, 5, 6, 7 – ADC0D, ADC1D, ADC2D, ADC3D, ADC4D, ADC5D, ADC6D, ADC7D:ꢀADC
Digital Input Disable
•
ADC:
–
When ADC0D or ADC1D is set to '1', 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 ADC[7:0] 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.
•
AC:
–
When ADC0D or ADC1D is set to '1', the digital input buffer on pin AIN1 (ADC1) / AIN0
(ADC0) is disabled and the corresponding PIN register bit will read as zero. When used as an
analog input but not required as a digital input the power consumption in the digital input
buffer can be reduced by writing this bit to logic one.
–
DIDR0[7:2] : these bits are not applicable for AC.
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19.
ADC - Analog to Digital Converter
19.1. Overview
ATtiny102/ATtiny104 feature an 10-bit, successive approximation ADC. The ADC is connected to a 8/5-
channel analog multiplexer for 14/8-pin device which allows 8/5 single-ended voltage inputs constructed
from the pins of port A and B, internal voltage reference, analog ground, or supply voltage. The single-
ended voltage inputs refer to 0V (GND).
19.2. Features
•
10-bit Resolution
•
•
•
•
•
•
•
•
•
•
•
•
1 LSB Integral Non-Linearity
±2 LSB Absolute Accuracy
15μs Conversion Time
15ksps at Maximum Resolution
8/5 Multiplexed Single Ended Input Channels on 14-pin/8-pin
Optional Left Adjustment for ADC Result Readout
Input Voltage Range: 0 - VCC
ADC Reference Voltages: 1.1V, 2.2V, and 4.3V
Free Running or Single Conversion Mode
ADC Start Conversion by Auto Triggering on Interrupt Sources
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler
19.3. Block Diagram
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.
Internal reference voltage of nominally 1.1V, 2.2V, and 4.3V is provided on-chip. Alternatively, VCC can be
used as reference voltage for single ended channels.
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Figure 19-1.ꢀAnalog to Digital Converter Block Schematic Operation
1.1V
2.2V
4.3V
19.4. Operation
The Power Reduction ADC bit in the Power Reduction Register (PRR.PRADC) must be written to '0' in
order to be enable the ADC.
The ADC is enabled by writing a '1' to the ADC Enable bit in the ADC Control and Status Register A
(ADCSRA.ADEN). Voltage reference and input channel selections will not take 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 converts an analog input voltage to an 10-bit digital value through successive approximation.
The minimum value represents GND and the maximum value represents the VREF voltage. The ADC
voltage reference is selected by writing the ADMUX.REFS[1:0] register.
The analog input channel is selected by writing to the MUX bits in the ADC Multiplexer Selection register
(ADMUX.MUX). Any of the ADC input pins can be selected as single ended inputs to the ADC.
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
ADCSRB.ADLAR.
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If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH, only.
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.
Related Links
PRR on page 44
ADMUX on page 177
ADCSRA on page 178
ADCSRB on page 180
ADCL and ADCH on page 182
ADCL and ADCH on page 183
19.5. Starting a Conversion
A single conversion is started by writing a '0' to the Power Reduction ADC bit in the Power Reduction
Register (PRR.PRADC), and writing a '1' to the ADC Start Conversion bit in the ADC Control and Status
Register A (ADCSRA.ADSC). ADCS will stay 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 (ADCSRA.ADATE). The trigger source is selected by setting
the ADC Trigger Select bits in the ADC Control and Status Register B (ADCSRB.ADTS). See the
description of the ADCSRB.ADTS for a list of available 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 the AVR Status REgister (SREG.I) 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.
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Figure 19-2.ꢀADC Auto Trigger Logic
ADTS[2:0]
PRESCALER
CLKADC
START
ADIF
ADATE
SOURCE 1
.
.
.
.
CONVERSION
LOGIC
EDGE
DETECTOR
SOURCE n
ADSC
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 '1' to
ADCSRA.ADSC. 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 ADCSRA.ADSC to '1'. ADSC
can also be used to determine if a conversion is in progress. The ADSC bit will be read as '1' during a
conversion, independently of how the conversion was started.
Related Links
PRR on page 44
19.6. Prescaling and Conversion Timing
By default, the successive approximation circuitry requires an input clock frequency between 50 kHz and
200 kHz to get maximum resolution.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency from any
CPU frequency above 100 kHz. The prescaling is selected by the ADC Prescaler Select bits in the ADC
Control and Status Register A (ADCSRA.ADPS). The prescaler starts counting from the moment the ADC
is switched on by writing the ADC Enable bit ADCSRA.ADEN to '1'. The prescaler keeps running for as
long as ADEN=1, and is continuously reset when ADEN=0.
Figure 19-3.ꢀADC Prescaler
ADEN
START
Reset
7-BIT ADC PRESCALER
CK
ADPS0
ADPS1
ADPS2
ADC CLOCK SOURCE
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When initiating a single ended conversion by writing a '1' to the ADC Start Conversion bit
(ADCSRA.ADSC), the conversion starts at the following rising edge of the ADC clock cycle.
A normal conversion takes 15 ADC clock cycles. The first conversion after the ADC is switched on (i.e.,
ADCSRA.ADEN is written to '1') takes 26 ADC clock cycles in order to initialize the analog circuitry, as the
figure below.
Figure 19-4.ꢀADC Timing Diagram, First Conversion (Single Conversion Mode)
Next
First Conversion
Conversion
Cycle Number
1
2
13
14
15
16
17
18
19
20
21
22
23
24
25
26
1
2
3
ADC Clock
ADEN
ADSC
ADIF
Sign and MSB of Result
LSB of Result
ADCH
ADCL
MUX and REFS
Update
Conversion
Complete
MUX and REFS
Update
Sample & Hold
The actual sample-and-hold takes place 4 ADC clock cycles after the start of a normal conversion and 15
ADC clock cycles after the start of an first conversion. When a conversion is complete, the result is written
to the ADC Data Registers (ADCL), and the ADC Interrupt Flag (ADCSRA.ADIF) is set. In Single
Conversion mode, ADCSRA.ADSC is cleared simultaneously. The software may then set
ADCSRA.ADSC again, and a new conversion will be initiated on the first rising ADC clock edge.
Figure 19-5.ꢀADC Timing Diagram, Single Conversion
One Conversion
Next Conversion
1
2
3
4
5
6
7
8
12
13
14
15
1
2
3
Cycle Number
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
LSB of Result
ADCL
Sample & Hold
Conversion
Complete
MUX and REFS
Update
MUX and REFS
Update
When Auto Triggering is used, the prescaler is reset when the trigger event occurs, as the next figure.
This assures a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-
hold takes place 4.5 ADC clock cycles after the rising edge on the trigger source signal. Two additional
CPU clock cycles are used for synchronization logic.
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Figure 19-6.ꢀADC Timing Diagram, Auto Triggered Conversion
One Conversion
Next Conversion
1
2
3
4
5
6
7
8
9
13
14
15
1
2
Cycle Number
ADC Clock
Trigger
Source
ADATE
ADIF
ADCH
ADCL
Sign and MSB of Result
LSB of Result
Sample &
Hold
Prescaler
Reset
Conversion
Complete
Prescaler
Reset
MUX and REFS
Update
In Free Running mode, a new conversion will be started immediately after the conversion completes,
while ADCRSA.ADSC remains high. See also the ADC Conversion Time table below.
Figure 19-7.ꢀADC Timing Diagram, Free Running Conversion
One Conversion
Next Conversion
13
14
15
1
2
3
4
5
Cycle Number
ADC Clock
ADSC
ADIF
ADCH
ADCL
Sign and MSB of Result
LSB of Result
Sample & Hold
MUX and REFS
Update
Conversion
Complete
Table 19-1.ꢀADC Conversion Time
Condition
Sample & Hold
(Cycles from Start of Conversion)
Conversion Time
(Cycles)
First conversion(1)
15
4
26
Normal conversions
15
Auto Triggered conversions
Free Running conversion
4.5
4
15.5
15
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Note:ꢀ
1. When gain amplifier is active, also includes the first conversion after a change in channel, reference
or gain setting.
19.7. Changing Channel or Reference Selection
The Analog Channel Selection bits (MUX) in the ADC Multiplexer Selection Register (ADCMUX.MUX) 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
selection is continuously updated until a conversion is started. Once the conversion starts, the channel
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 (indicated by ADCSRA.ADIF 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 the ADC
Start Conversion bit (ADCRSA.ADSC) was 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 the ADC Auto Trigger Enable (ADCRSA.ADATE) and ADC Enable bits (ADCRSA.ADEN) are
written to '1', 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.
1.1.
1.2.
During conversion, minimum one ADC clock cycle after the trigger event.
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.
19.8. 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.
The user is advised not to write new channel or reference selection values during Free Running mode.
19.9. ADC Voltage Reference
The reference voltage for the ADC (VREF) indicates the conversion range, which in this case is limited to
0V (VGND) and VREF = Vcc. Single ended channels that exceed VREF will result in codes close to 0x3FF.
VREF can be selected from VCC or internal reference. The internal voltage reference can be set to 1.1, 2.2,
or 4.3V and is generated from the internal bandgap reference (VBG) through an internal amplifier. The first
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ADC conversion result after switching reference voltage source may be inaccurate, and the user is
advised to discard this result.
19.10. 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:ꢀ 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 ADCRSA.ADEN before entering such
sleep modes to avoid excessive power consumption.
19.11. Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated below. 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 10 kΩ 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 impedance sources with slowly varying signals, since
this minimizes the required charge transfer to the S/H capacitor.
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.
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Figure 19-8.ꢀAnalog Input Circuitry
I
IH
ADCn
1..100kΩ
C = 14pF
S/H
I
IL
VCC/2
19.12. 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:
•
•
•
•
•
Keep analog signal paths as short as possible.
Make sure analog tracks run over the analog ground plane
Keep analog tracks well away from high-speed switching digital tracks.
If any port pin is used as a digital output, it mustn’t switch while a conversion is in progress.
Place bypass capacitors as close to VCC and GND pins as possible.
When high ADC accuracy is required it is recommended to use ADC Noise Reduction Mode. A good
system design with properly placed, external bypass capacitors does reduce the need for using ADC
Noise Reduction Mode.
19.13. 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.
Several parameters describe the deviation from the ideal behavior:
•
Offset: The deviation of the first transition (0x00 to 0x01) compared to the ideal transition (at 0.5
LSB). Ideal value: 0 LSB.
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Figure 19-9.ꢀ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
(0xFE to 0xFF) compared to the ideal transition (at 1.5 LSB below maximum). Ideal value: 0 LSB.
Figure 19-10.ꢀGain Error
Gain
Error
Output Code
Ideal ADC
Actual ADC
V
Input Voltage
REF
•
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 19-11.ꢀIntegral Non-linearity (INL)
Output Code
Ideal ADC
Actual ADC
V
Input Voltage
REF
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•
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 19-12.ꢀ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.
19.14. ADC Conversion Result
After the conversion is complete (ADCSRA.ADIF is set), the conversion result can be found in the ADC
Result Registers (ADCL and ADCH).
ADCL must be read first in order to avoid locking the data registers from getting updated by the next
conversion result. The form of the conversion result depends on the type of conversion.
19.14.1. Single-Ended Conversion
For single-ended conversion, the result is as follows
ꢐ
⋅ 1024
IN
ADC =
ꢐ
ꢇꢌꢊ
where VIN is the voltage on the selected input pin, and VREF the selected voltage reference (see also
descriptions of ADMUX.MUX). 0x00 represents analog ground, and 0x3FF represents the selected
reference voltage minus one LSB. The result is presented in one-sided form, from 0x3FF to 0x000.
Note:ꢀ 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.
19.15. Register Description
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19.15.1. ADC Multiplexer Selection Register
Name:ꢀ ADMUX
Offset:ꢀ 0x1B
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
REFS1
R/W
0
6
REFS0
R/W
0
5
4
3
2
MUX2
R/W
0
1
MUX1
R/W
0
0
MUX0
R/W
0
Access
Reset
Bits 7:6 – REFSn:ꢀReference Selection [n = 1:0]
These bits select the voltage reference for the ADC. 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 19-3.ꢀADC Voltage Reference Selection
REFS[1:0]
Voltage Reference Selection
Vcc
00
01
10
11
Internal 1.1V reference
Internal 2.2V reference
Internal 4.3V reference
Bits 2:0 – MUXn:ꢀAnalog Channel Selection [n = 2:0]
The value of these bits selects which analog inputs are connected to the ADC. If these bits are changed
during a conversion, the change will not go in effect until this conversion is complete (ADCSRA.ADIF is
set).
Table 19-2.ꢀInput Channel Selection
MUX[2:0]
000
Single Ended Input
ADC0
Pin name
PA[0]
001
ADC1
PA[1]
010
ADC2
PA[5]
011
ADC3
PA[6]
100
ADC4
PB[0]
PB[1]
PB[2]
PB[3]
101
ADC5
110
ADC6
111
ADC7
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19.15.2. ADC Control and Status Register A
Name:ꢀ ADCSRA
Offset:ꢀ 0x1D
Reset:ꢀ 0x00
Property: -
ꢀ
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
Access
Reset
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 – ADPSn:ꢀADC Prescaler Select [n = 2:0]
These bits determine the division factor between the system clock frequency and the input clock to the
ADC.
Table 19-4.ꢀInput Channel Selection
ADPS[2:0]
000
Division Factor
2
2
001
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ADPS[2:0]
010
Division Factor
4
011
8
100
16
32
64
128
101
110
111
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19.15.3. ADC Control and Status Register B
Name:ꢀ ADCSRB
Offset:ꢀ 0x1C
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
ADLAR
R/W
0
6
5
4
3
2
ADTS2
R/W
0
1
ADTS1
R/W
0
0
ADTS0
R/W
0
Access
Reset
Bit 7 – ADLAR:ꢀLeft Adjustment for ADC Result Readout
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.
ADLAR = 0
Bit
15
14
13
12
11
10
9
8
0x1A
0x19
–
–
–
–
–
–
ADC9
ADC1
ADC8
ADC0
ADCH
ADCL
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
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
ADLAR = 1
Bit
15
14
13
12
11
10
9
8
0x1A
0x19
ADC9
ADC1
7
R
R
0
ADC8
ADC0
6
R
R
0
ADC7
–
5
R
R
0
ADC6
–
4
R
R
0
ADC5
–
3
R
R
0
ADC4
–
2
R
R
0
ADC3
–
1
R
R
0
ADC2
–
0
R
R
0
ADCH
ADCL
Read/Write
Initial Value
0
0
0
0
0
0
0
0
Bits 2:0 – ADTSn:ꢀADC Auto Trigger Source [n = 2:0]
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 19-5.ꢀADC Auto Trigger Source Selection
ADTS[2:0]
000
Trigger Source
Free Running mode
Analog Comparator
External Interrupt Request 0
001
010
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ADTS[2:0]
011
Trigger Source
Timer/Counter 0 Compare Match A
Timer/Counter 0 Overflow
100
101
Timer/Counter 0 Compare Match B
Pin Change Interrupt 0 Request
Timer/Counter 0 Capture Event
110
111
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19.15.4. ADC Data Register Low and High Byte (ADLAR=0)
The ADCL and ADCH register pair represents the 16-bit value, ADC Data Register. The low byte [7:0]
(suffix L) is accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset +
0x01. For more details on reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
When an ADC conversion is complete, the result is found in these two registers.
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 and the MUXn bits in ADMUX affect the way the result is read from the registers. If
ADLAR is set (ADLAR=1), the result is left adjusted. If ADLAR is cleared (ADLAR=0 which is the default
value), the result is right adjusted.
Name:ꢀ ADCL and ADCH
Offset:ꢀ 0x19
Reset:ꢀ 0x00
Property: ADLAR = 0
ꢀ
Bit
15
14
13
12
11
10
9
ADC9
R
8
ADC8
R
Access
Reset
0
0
Bit
7
ADC7
R
6
ADC6
R
5
ADC5
R
4
ADC4
R
3
ADC3
R
2
ADC2
R
1
ADC1
R
0
ADC0
R
Access
Reset
0
0
0
0
0
0
0
0
Bits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 – ADCn:ꢀADC Conversion Result
These bits represent the result from the conversion. Refer to ADC Conversion Result for details.
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19.15.5. ADC Data Register Low and High Byte (ADLAR=1)
The ADCL and ADCH register pair represents the 16-bit value, ADC Data Register. The low byte [7:0]
(suffix L) is accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset +
0x01. For more details on reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
When an ADC conversion is complete, the result is found in these two registers.
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 and the MUXn bits in ADMUX affect the way the result is read from the registers. If
ADLAR is set (ADLAR=1), the result is left adjusted. If ADLAR is cleared (ADLAR=0 which is the default
value), the result is right adjusted.
Name:ꢀ ADCL and ADCH
Offset:ꢀ 0x19
Reset:ꢀ 0x00
Property: ADLAR = 1
ꢀ
Bit
15
ADC9
R
14
ADC8
R
13
ADC7
R
12
ADC6
R
11
ADC5
R
10
ADC4
R
9
ADC3
R
8
ADC2
R
Access
Reset
0
0
0
0
0
0
0
0
Bit
7
ADC1
R
6
ADC0
R
5
4
3
2
1
0
Access
Reset
0
0
Bits 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 – ADCn:ꢀADC Conversion Result
These bits represent the result from the conversion. Refer to ADC Conversion Result for details.
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19.15.6. Digital Input Disable Register 0
When the respective bits are written to 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 ADC[7:0] 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.
Name:ꢀ DIDR0
Offset:ꢀ 0x17
Reset:ꢀ 0x00
Property: -
ꢀ
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
Access
Reset
Bits 0, 1, 2, 3, 4, 5, 6, 7 – ADC0D, ADC1D, ADC2D, ADC3D, ADC4D, ADC5D, ADC6D, ADC7D:ꢀADC
Digital Input Disable
•
ADC:
–
When ADC0D or ADC1D is set to '1', 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 ADC[7:0] 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.
•
AC:
–
When ADC0D or ADC1D is set to '1', the digital input buffer on pin AIN1 (ADC1) / AIN0
(ADC0) is disabled and the corresponding PIN register bit will read as zero. When used as an
analog input but not required as a digital input the power consumption in the digital input
buffer can be reduced by writing this bit to logic one.
–
DIDR0[7:2] : these bits are not applicable for AC.
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20.
MEMPROG- Memory Programming
20.1. Overview
The Non-Volatile Memory (NVM) Controller manages all access to the Non-Volatile Memories. The NVM
Controller controls all NVM timing and access privileges, and holds the status of the NVM.
During normal execution the CPU will execute code from the code section of the Flash memory (program
memory). When entering sleep and no programming operations are active, the Flash memory is disabled
to minimize power consumption.
All NVM are mapped to the data memory. Application software can read the NVM from the mapped
locations of data memory using load instruction with indirect addressing.
The NVM has only one read port and, therefore, the next instruction and the data can not be read
simultaneously. When the application reads data from NVM locations mapped to the data space, the data
is read first before the next instruction is fetched. The CPU execution is here delayed by one system
clock cycle.
Internal programming (self-programming) operations to NVM have been disabled and the NVM therefore
appears to the application software as read-only. Internal write or erase operations of the NVM will not be
successful.
The method used by the external programmer for writing the Non-Volatile Memories is referred to as
external programming. External programming can be done both in-system or in mass production. The
external programmer can read and program the NVM via the Tiny Programming Interface (TPI).
In the external programming mode all NVM can be read and programmed, except the signature and the
calibration sections which are read-only.
NVM can be programmed between 1.8-5.5V.
20.2. Features
•
Two Embedded Non-Volatile Memories:
–
–
Non-Volatile Memory Lock bits (NVM Lock bits)
Flash Memory
•
Four Separate Sections Inside Flash Memory:
–
–
–
–
Code Section (Program Memory)
Signature Section
Configuration Section
Calibration Section
•
•
Read Access to All Non-Volatile Memories from Application Software
Read and Write Access to Non-Volatile Memories from External programmer:
–
–
Read Access to All Non-Volatile Memories
Write Access to NVM Lock Bits, Flash Code Section and Flash Configuration Section
•
•
External Programming:
–
–
Support for In-System and Mass Production Programming
Programming Through the Tiny Programming Interface (TPI)
High Security with NVM Lock Bits
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•
Self-Programming Flash on Full Operating Voltage Range (1.8 – 5.5V)
20.3. Non-Volatile Memories (NVM)
The device has the following, embedded NVM:
•
•
•
Non-Volatile Memory Lock Bits
Flash memory with four separate sections
1KB Flash Memory
–
CPU execution will be halted while doing external programming
Extra rows
Flash - Unique ID needs to be added
•
–
20.3.1. Non-Volatile Memory Lock Bits
The device provides two Lock Bits.
Table 20-1.ꢀLock Bit Byte
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)
NVLB2
NVLB1
Non-Volatile Lock Bit
Non-Volatile Lock Bit
The Lock Bits can be left unprogrammed ("1") or can be programmed ("0") to obtain the additional
security. Lock Bits can be erased to "1" with the Chip Erase command, only.
Table 20-2.ꢀLock Bit Protection Modes
Memory Lock Bits(1)
Protection Type
LB Mode NVLB2(2) NVLB1(2)
1
2
1
1
1
0
No memory lock features enabled.
Further Programming of the Flash memory is disabled in the external
programming mode. The configuration section bits are locked in the
external programming mode
3
0
0
Further programming and verification of the flash is disabled in the
external programming mode. The configuration section bits are locked
in the external programming mode
Note:ꢀ
1. Program the configuration section bits before programming NVLB1 and NVLB2.
2. "1" means unprogrammed, "0" means programmed
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20.3.2. Flash Memory
The embedded Flash memory has four separate sections.
Table 20-3.ꢀNumber of Words and Pages in the Flash
Section
Size (Bytes)
Page Size
(Words)
Pages
WADDR
PADDR
Code (program 1024
memory)
8
64
[3:1]
[9:4]
Configuration
Signature (1)
Calibration(1)
8
8
8
8
1
2
1
[3:1]
[3:1]
[3:1]
-
16
8
[4:4]
-
Note:ꢀ
1. This section is read-only.
20.3.3. Configuration Section
ATtiny102/ATtiny104 have one configuration byte, which resides in the configuration section.
Table 20-4.ꢀConfiguration bytes
Configuration byte Offset Address Configuration word data
CONFW0
0x04
Configuration word (fuse values- RSTDISBL, WDTON, CKOUT,
SELFPROGEN)
The next table briefly describes the functionality of all configuration bits and how they are mapped into the
configuration byte.
Table 20-5.ꢀConfiguration Byte 0
Bit
7:4
3
Fuse values
–
Description
Default Value
Reserved
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
SELFPROGEN
CKOUT
Self-Programming
System Clock Output
Watchdog Timer always on
External Reset disable
2
1
WDTON
0
RSTDISBL
Configuration bits are not affected by a chip erase but they can be cleared using the configuration section
erase command (see Erasing the Configuration Section in this chapter). Note that configuration bits are
locked if Non- Volatile Lock Bit 1 (NVLB1) is programmed.
20.3.3.1. Latching of Configuration Bits
All configuration bits are latched either when the device is reset or when the device exits the external
programming mode. Changes to configuration bit values have no effect until the device leaves the
external programming mode.
20.3.4. Signature Section
The signature section is a dedicated memory area used for storing miscellaneous device information,
such as the device signature. Most of this memory section is reserved for internal use.
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ATtiny102/ATtiny104 have a three-byte signature code, which can be used to identify the device. The
three bytes reside in the signature section, as shown in the above table. The signature data for
ATtiny102/ATtiny104 is given in the next table.
Table 20-6.ꢀSignature bytes
Signature word address
Configuration word data
High byte
Low byte
0x00
Device ID 1
Manufacturer ID
Device ID 2
0x01
Reserved for internal use
Reserved for internal use
Serial number
0x02
0x03 ... 0x07
Table 20-7.ꢀSignature codes
Part
Signature Bytes
Manufacturer ID
0x1E
Device ID 1
0x90
Device ID 2
0x0C
ATtiny102
ATtiny104
0x1E
0x90
0x0B
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20.3.4.1. Signature Row Summary
Offset
Name
Bit Pos.
SIGROW_DEVICEI
0x00
7:0
DEVICEID[7:0]
DEVICEID[7:0]
DEVICEID[7:0]
D0
SIGROW_DEVICEI
0x01
0x02
7:0
7:0
D1
SIGROW_DEVICEI
D2
0x03
...
Reserved
0x05
SIGROW_SERNUM
0x06
0x07
0x08
0x09
0x0A
0x0B
0x0C
0x0D
0x0E
0x0F
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
SERNUM[7:0]
SERNUM[7:0]
SERNUM[7:0]
SERNUM[7:0]
SERNUM[7:0]
SERNUM[7:0]
SERNUM[7:0]
SERNUM[7:0]
SERNUM[7:0]
SERNUM[7:0]
0
SIGROW_SERNUM
1
SIGROW_SERNUM
2
SIGROW_SERNUM
3
SIGROW_SERNUM
4
SIGROW_SERNUM
5
SIGROW_SERNUM
6
SIGROW_SERNUM
7
SIGROW_SERNUM
8
SIGROW_SERNUM
9
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Device ID n
Name:ꢀ SIGROW_DEVICEIDn
Offset:ꢀ 0x00 + n*0x01 [n=0..2]
Reset:ꢀ [Device ID]
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
DEVICEID[7:0]
Access
Reset
R
0
R
0
R
0
R
0
R
0
R
0
R
0
R
0
Bits 7:0 – DEVICEID[7:0]:ꢀByte n of the Device ID
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Serial Number Byte n
Name:ꢀ SIGROW_SERNUMn
Offset:ꢀ 0x06 + n*0x01 [n=0..9]
Reset:ꢀ [device serial number]
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
SERNUM[7:0]
Access
Reset
R
x
R
x
R
x
R
x
R
x
R
x
R
x
R
x
Bits 7:0 – SERNUM[7:0]:ꢀSerial Number n [n=0..9]
Each device has an individual serial number, representing a unique ID. This can be used to identify a
specific device in the field. The serial number consists of ten bytes..
20.3.5. Calibration Section
ATtiny102/ATtiny104 have one calibration byte. The calibration byte contains the calibration data for the
internal oscillator and resides in the calibration section. During reset, the calibration byte is automatically
written into the OSCCAL register to ensure correct frequency of the calibrated internal oscillator.
Table 20-8.ꢀCalibration byte
Calibration byte
Offset Address
Configuration word data
High byte [BYTE1]
Reserved
Low byte [BYTE0]
Oscillator calibration value
Reserved
OSCCAL
Reserved
0x00
0x01 ... 0x07
Reserved
20.4. Accessing the NVM
NVM lock bits, and all Flash memory sections are mapped to the data space as shown in Data Memory.
The NVM can be accessed for read and programming via the locations mapped in the data space.
The NVM Controller recognizes a set of commands that can be used to instruct the controller what type of
programming task to perform on the NVM. Commands to the NVM Controller are issued via the NVM
Command Register. See NVMCMD - Non-Volatile Memory Command Register. After the selected
command has been loaded, the operation is started by writing data to the NVM locations mapped to the
data space.
When the NVM Controller is busy performing an operation it will signal this via the NVM Busy Flag in the
NVM Control and Status Register. See NVMCSR - Non-Volatile Memory Control and Status Register. The
NVM Command Register is blocked for write access as long as the busy flag is active. This is to ensure
that the current command is fully executed before a new command can start.
Programming any part of the NVM will automatically inhibit the following operations:
•
•
All programming to any other part of the NVM
All reading from any NVM location
ATtiny102/ATtiny104 supports external programming and internal programming (self-programming).
Related Links
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SRAM Data Memory on page 27
NVMCSR on page 196
NVMCMD on page 197
20.4.1. Addressing the Flash
The data space uses byte accessing but since the Flash sections are accessed as words and organized
in pages, the byte-address of the data space must be converted to the word-address of the Flash section.
The most significant bits of the data space address select the NVM Lock bits or the Flash section mapped
to the data memory. The word address within a page (WADDR) is held by bits [WADDRMSB:1], and the
page address (PADDR) by bits [PADDRMSB:WADDRMSB+1]. Together, PADDR and WADDR form the
absolute address of a word in the Flash section.
The least significant bit of the Flash section address is used to select the low or high byte of the word.
Figure 20-1.ꢀAddressing the Flash Memory
16
PADDRMSB
WADDRMSB+1 WADDRMSB
1
PADDR
WADDR
0/1
ADDRESS POINTER
LOW/HIGH
BYTE SELECT
FLASH
SECTION
FLASH
PAGE
00
01
02
...
00
WORD ADDRESS
WITHIN A FLASH
PAGE
01
...
...
...
WORD
PAGE
PAGE ADDRESS
WITHIN A FLASH
SECTION
...
...
PAGEEND
SECTIONEND
20.4.2. Reading the Flash
The Flash can be read from the data memory mapped locations one byte at a time. For read operations,
the least significant bit (bit 0) is used to select the low or high byte in the word address. If this bit is zero,
the low byte is read, and if it is one, the high byte is read.
20.4.3. Programming the Flash
The Flash can be written word-by-word. Before writing a Flash word, the Flash target location must be
erased. Writing to an un-erased Flash word will corrupt its content.
The Flash is word-accessed for writing, and the data space uses byte-addressing to access Flash that
has been mapped to data memory. It is therefore important to write the word in the correct order to the
Flash, namely low bytes before high bytes. First, the low byte is written to the temporary buffer. Then,
writing the high byte latches both the high byte and the low byte into the Flash word buffer, starting the
write operation to Flash.
The Flash erase operations can only performed for the entire Flash sections.
The Flash programming sequence is as follows:
1. Perform a Flash section erase or perform a Chip erase
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2. Write the Flash section word by word
20.4.3.1. Chip Erase
The Chip Erase command will erase the entire code section of the Flash memory and the NVM Lock Bits.
For security reasons, the NVM Lock Bits are not reset before the code section has been completely
erased. Configuration, Signature and Calibration sections are not changed.
Before starting the Chip erase, the NVMCMD register must be loaded with the CHIP_ERASE command.
To start the erase operation a dummy byte must be written into the high byte of a word location that
resides inside the Flash code section. The NVMBSY bit remains set until erasing has been completed.
While the Flash is being erased neither Flash buffer loading nor Flash reading can be performed.
The Chip Erase can be carried out as follows:
1. Write the 0x10 (CHIP_ERASE) to the NVMCMD register
2. Start the erase operation by writing a dummy byte to the high byte of any word location inside the
code section
3. Wait until the NVMBSY bit has been cleared
20.4.3.2. Erasing the Code Section
The algorithm for erasing all pages of the Flash code section is as follows:
1. Write the 0x14 (SECTION_ERASE) to the NVMCMD register
2. Start the erase operation by writing a dummy byte to the high byte of any word location inside the
code section
3. Wait until the NVMBSY bit has been cleared
20.4.3.3. Writing a Code Word
The algorithm for writing a word to the code section is as follows:
1. Write the 0x1D (WORD_WRITE) to the NVMCMD register
2. Write the low byte of the data into the low byte of a word location
3. Write the high byte of the data into the high byte of the same word location. This will start the Flash
write operation
4. Wait until the NVMBSY bit has been cleared
20.4.3.4. Erasing the Configuration Section
The algorithm for erasing the Configuration section is as follows:
1. Write the 0x14 (SECTION_ERASE) to the NVMCMD register
2. Start the erase operation by writing a dummy byte to the high byte of any word location inside the
configuration section
3. Wait until the NVMBSY bit has been cleared
20.4.3.5. Writing a Configuration Word
The algorithm for writing a Configuration word is as follows:
1. Write the 0x1D (WORD_WRITE) to the NVMCMD register
2. Write the low byte of the data to the low byte of a configuration word location
3. Write the high byte of the data to the high byte of the same configuration word location. This will
start the Flash write operation.
4. Wait until the NVMBSY bit has been cleared
20.4.4. Reading NVM Lock Bits
The Non-Volatile Memory Lock Byte can be read from the mapped location in data memory.
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20.4.5. Writing NVM Lock Bits
The algorithm for writing the Lock bits is as follows:
1. Write the WORD_WRITE command to the NVMCMD register.
2. Write the lock bits value to the Non-Volatile Memory Lock Byte location. This is the low byte of the
Non- Volatile Memory Lock Word.
3. Start the NVM Lock Bit write operation by writing a dummy byte to the high byte of the NVM Lock
Word location.
4. Wait until the NVMBSY bit has been cleared.
20.5. Self programming
The Flash in Tiny104 does not support Read-While-Write, and cannot be read during an erase or write
operation. Therefore, the CPU will halt execution.
The device provides a Self-Programming mechanism for downloading and uploading program code by
the MCU itself. Only WORD_WRITE and PAGE_ERASE commands are supported in self-programming.
The CPU can execute Page Erase and Word Write in the NVM code memory section to perform
programming operations.
Note:ꢀ The user needs to add two NOP operations after the ST operation that triggers the self-
programming to ensure correct CPU operation.
Table 20-9.ꢀExample code for self-programming:
Assembly Code Example
The sequence for entering self-programming mode is given below (r19 can be any register):
;
ldi
out
set CCP
r19, 0xe7
CCP, r19
The software then has to perform the desired self-programming operation within 4 clock cycles.
Example of the complete code to perform page erase:
;
erase page
set the page address pointer
ZL, 0xE1
;
ldi
ldi
;
ldi
out
;
ZH, 0x43
set NVMCMD to page erase
temp, 0b011000
NVMCMD, temp
set CCP to enter program mode
r19, 0xe7
ldi
out
CCP, r19
; trigger the erase operation (within four clock cycles)
ldi
st
temp, 0x00
Z+, temp
; required for proper CPU halting
nop
nop
20.6. External Programming
The method for programming the Non-Volatile Memories by means of an external programmer is referred
to as external programming. External programming can be done both in-system or in mass production.
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The Non-Volatile Memories can be externally programmed via the Tiny Programming Interface (TPI). For
details on the TPI, see Programming interface. Using the TPI, the external programmer can access the
NVM control and status registers mapped to I/O space and the NVM memory mapped to data memory
space.
Related Links
TPI-Tiny Programming Interface on page 198
20.6.1. Entering External Programming Mode
The TPI must be enabled before external programming mode can be entered. The following procedure
describes, how to enter the external programming mode after the TPI has been enabled:
1. Make a request for enabling NVM programming by sending the NVM memory access key with the
SKEY instruction.
2. Poll the status of the NVMEN bit in TPISR until it has been set.
Refer to the Programming Interface description for more detailed information of enabling the TPI and
programming the NVM.
Related Links
TPI-Tiny Programming Interface on page 198
20.6.2. Exiting External Programming Mode
Clear the NVM enable bit to disable NVM programming, then release the RESET pin.
See NVMEN bit in TPISR – Tiny Programming Interface Status Register.
Related Links
TPISR on page 209
20.7. Register Description
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20.7.1. Non-Volatile Memory Control and Status Register
Name:ꢀ NVMCSR
Offset:ꢀ 0x32
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
NVMBSY
R/W
6
5
4
3
2
1
0
Access
Reset
0
Bit 7 – NVMBSY:ꢀNon-Volatile Memory Busy
This bit indicates the NVM memory (Flash memory and Lock Bits) is busy, being programmed. This bit is
set when a program operation is started, and it remains set until the operation has been completed.
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20.7.2. Non-Volatile Memory Command Register
Name:ꢀ NVMCMD
Offset:ꢀ 0x33
Reset:ꢀ 0x00
Property: -
ꢀ
Bit
7
6
5
4
3
2
1
0
NVMCMD[5:0]
Access
Reset
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
Bits 5:0 – NVMCMD[5:0]:ꢀNon-Volatile Memory Command
These bits define the programming commands for the flash.
Table 20-10.ꢀNVM Programming commands
Operation Type
NVMCMD
Binary
Mnemonic
Description
Hex
General
0b000000
0b010000
0b010001
0b010100
0b011101
0b011000
0x00
0x10
0x11
0x14
0x1D
0x18
NO_OPERATION
CHIP_ERASE
No operation
Chip erase(1)
Write chip(2)
CHIP_WRITE
Section
Word
SECTION_ERASE
WORD_WRITE
PAGE_ERASE
Section erase
Word write
Page
Erase page
Note:ꢀ
1. Erase the Code section and the Non-Volatile Memory lock bits.
2. Write the Code section, but doesn't affect the Non-Volatile Memory lock bits. Self-programming
supports NO_OPERATION, WORD_WRITE, and PAGE_ERASE
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21.
TPI-Tiny Programming Interface
21.1. Overview
The Tiny Programming Interface (TPI) supports external programming of all Non-Volatile Memories
(NVM). Memory programming is done via the NVM Controller, by executing NVM controller commands as
described in Memory Programming.
Related Links
MEMPROG- Memory Programming on page 185
21.2. Features
•
Physical Layer:
–
–
–
–
–
Synchronous Data Transfer
Bi-directional, Half-duplex Receiver And Transmitter
Fixed Frame Format With One Start Bit, 8 Data Bits, One Parity Bit And 2 Stop Bits
Parity Error Detection, Frame Error Detection And Break Character Detection
Parity Generation And Collision Detection – Automatic Guard Time Insertion Between Data
Reception And Transmission
•
Access Layer:
–
–
–
–
–
–
Communication Based On Messages
Automatic Exception Handling Mechanism
Compact Instruction Set
NVM Programming Access Control
Tiny Programming Interface Control And Status Space Access Control
Data Space Access Control
21.3. Block Diagram
The Tiny Programming Interface (TPI) provides access to the programming facilities. The interface
consists of two layers: the access layer and the physical layer.
Figure 21-1.ꢀThe Tiny Programming Interface and Related Internal Interfaces
NVM
CONTROLLER
TINYPROGRAMMING INTERFACE (TPI)
RESET
PHYSICAL
LAYER
ACCESS
LAYER
TPICLK
NON-VOLATILE
MEMORIES
TPIDATA
DATABUS
Programming is done via the physical interface. This is a 3-pin interface, which uses the RESET pin as
enable, the TPICLK pin as the clock input, and the TPIDATA pin as data input and output. NVM can be
programmed between 1.8-5.5V.
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21.4. Physical Layer of Tiny Programming Interface
The TPI physical layer handles the basic low-level serial communication. The TPI physical layer uses a
bi-directional, half-duplex serial receiver and transmitter. The physical layer includes serial-to-parallel and
parallel-to-serial data conversion, start-of-frame detection, frame error detection, parity error detection,
parity generation and collision detection.
The TPI is accessed via three pins, as follows:
•
•
•
RESET: Tiny Programming Interface enable input
TPICLK: Tiny Programming Interface clock input
TPIDATA: Tiny Programming Interface data input/output
In addition, the VCC and GND pins must be connected between the external programmer and the device.
21.4.1. Enabling
The following sequence enables the Tiny Programming Interface:
•
•
Apply 5V between VCC and GND
Depending on the method of reset to be used:
–
Either: wait tTOUT (see System and Reset Characteristics) and then set the RESET pin low.
This will reset the device and enable the TPI physical layer. The RESET pin must then be
kept low for the entire programming session
–
Or: if the RSTDISBL configuration bit has been programmed, apply 12V to the RESET pin.
The RESET pin must be kept at 12V for the entire programming session
•
•
Wait tRST (see System and Reset Characteristics )
Keep the TPIDATA pin high for 16 TPICLK cycles
Figure 21-2.ꢀSequence for enabling the Tiny Programming Interface
t
16 x TPICLK CYCLES
RST
RESET
TPICLK
TPIDATA
Related Links
System and Reset Characteristics on page 214
21.4.2. Disabling
Provided that the NVM enable bit has been cleared, the TPI is automatically disabled if the RESET pin is
released to inactive high state or, alternatively, if VHV is no longer applied to the RESET pin.
If the NVM enable bit is not cleared a power down is required to exit TPI programming mode. See
NVMEN bit in TPISR – Tiny Programming Interface Status Register.
Related Links
TPISR on page 209
21.4.3. Frame Format
The TPI physical layer supports a fixed frame format. A frame consists of one character, eight bits in
length, and one start bit, a parity bit and two stop bits. Data is transferred with the least significant bit first.
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Figure 21-3.ꢀSerial frame format.
TPICLK
TPIDATA
IDLE
ST
D0
D1
D7
P
SP1
SP2
IDLE/ST
Symbols used in the above figure:
•
•
•
•
•
ST: Start bit (always low)
D0-D7: Data bits (least significant bit sent first)
P: Parity bit (using even parity)
SP1: Stop bit 1 (always high)
SP2: Stop bit 2 (always high)
21.4.4. Parity Bit Calculation
The parity bit is always calculated using even parity. The value of the bit is calculated by doing an
exclusive-or of all the data bits, as follows:
ꢅ = ꢈ0 ⊗ ꢈ1 ⊗ ꢈ2 ⊗ ꢈ3 ⊗ ꢈ4 ⊗ ꢈ5 ⊗ ꢈ6 ⊗ ꢈ7 ⊗ 0
where:
•
•
P: Parity bit using even parity
D0-D7: Data bits of the character
21.4.5. Supported Characters
The BREAK character is equal to a 12 bit long low level. It can be extended beyond a bit-length of 12.
Figure 21-4.ꢀSupported characters.
DATA CHARACTER
TPIDATA
TPIDATA
IDLE
IDLE
ST
D0
D1
D7
P
SP1
SP2
IDLE/ST
IDLE/ST
BREAK CHARACTER
21.4.6. Operation
The TPI physical layer operates synchronously on the TPICLK provided by the external programmer. The
dependency between the clock edges and data sampling or data change is shown in the figure below.
Data is changed at falling edges and sampled at rising edges.
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Figure 21-5.ꢀData changing and Data sampling.
TPICLK
TPIDATA
SAMPLE
SETUP
The TPI physical layer supports two modes of operation: Transmit and Receive. By default, the layer is in
Receive mode, waiting for a start bit. The mode of operation is controlled by the access layer.
21.4.7. Serial Data Reception
When the TPI physical layer is in receive mode, data reception is started as soon as a start bit has been
detected. Each bit that follows the start bit will be sampled at the rising edge of the TPICLK and shifted
into the shift register until the second stop bit has been received. When the complete frame is present in
the shift register the received data will be available for the TPI access layer.
There are three possible exceptions in the receive mode: frame error, parity error and break detection. All
these exceptions are signalized to the TPI access layer, which then enters the error state and puts the
TPI physical layer into receive mode, waiting for a BREAK character.
•
Frame Error Exception. The frame error exception indicates the state of the stop bit. The frame
error exception is set if the stop bit was read as zero.
•
Parity Error Exception. The parity of the data bits is calculated during the frame reception. After the
frame is received completely, the result is compared with the parity bit of the frame. If the
comparison fails the parity error exception is signalized.
•
Break Detection Exception. The Break detection exception is given when a complete frame of all
zeros has been received.
21.4.8. Serial Data Transmission
When the TPI physical layer is ready to send a new frame it initiates data transmission by loading the shift
register with the data to be transmitted. When the shift register has been loaded with new data, the
transmitter shifts one complete frame out on the TPIDATA line at the transfer rate given by TPICLK.
If a collision is detected during transmission, the output driver is disabled. The TPI access layer enters the
error state and the TPI physical layer is put into receive mode, waiting for a BREAK character.
21.4.9. Collision Detection Exception
The TPI physical layer uses one bi-directional data line for both data reception and transmission. A
possible drive contention may occur, if the external programmer and the TPI physical layer drive the
TPIDATA line simultaneously. In order to reduce the effect of the drive contention, a collision detection
mechanism is supported. The collision detection is based on the way the TPI physical layer drives the
TPIDATA line.
The TPIDATA line is driven by a tri-state, push-pull driver with internal pull-up. The output driver is always
enabled when a logical zero is sent. When sending successive logical ones, the output is only driven
actively during the first clock cycle. After this, the output driver is automatically tri-stated and the TPIDATA
line is kept high by the internal pull-up. The output is re-enabled, when the next logical zero is sent.
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The collision detection is enabled in transmit mode, when the output driver has been disabled. The data
line should now be kept high by the internal pull-up and it is monitored to see, if it is driven low by the
external programmer. If the output is read low, a collision has been detected.
There are some potential pit-falls related to the way collision detection is performed. For example,
collisions cannot be detected when the TPI physical layer transmits a bit-stream of successive logical
zeros, or bit-stream of alternating logical ones and zeros. This is because the output driver is active all the
time, preventing polling of the TPIDATA line. However, within a single frame the two stop bits should
always be transmitted as logical ones, enabling collision detection at least once per frame (as long as the
frame format is not violated regarding the stop bits).
The TPI physical layer will cease transmission when it detects a collision on the TPIDATA line. The
collision is signalized to the TPI access layer, which immediately changes the physical layer to receive
mode and goes to the error state. The TPI access layer can be recovered from the error state only by
sending a BREAK character.
21.4.10. Direction Change
In order to ensure correct timing of the half-duplex operation, a simple guard time mechanism has been
added to the physical layer. When the TPI physical layer changes from receive to transmit mode, a
configurable number of additional IDLE bits are inserted before the start bit is transmitted. The minimum
transition time between receive and transmit mode is two IDLE bits.
The total IDLE time is the specified guard time plus two IDLE bits. The guard time is configured by
dedicated bits in the TPIPCR register. The default guard time value after the physical layer is initialized is
128 bits.
The external programmer looses control of the TPIDATA line when the TPI target changes from receive
mode to transmit. The guard time feature relaxes this critical phase of the communication. When the
external programmer changes from receive mode to transmit, a minimum of one IDLE bit should be
inserted before the start bit is transmitted.
21.4.11. Access Layer of Tiny Programming Interface
The TPI access layer is responsible for handling the communication with the external programmer. The
communication is based on message format, where each message comprises an instruction followed by
one or more byte-sized operands. The instruction is always sent by the external programmer but
operands are sent either by the external programmer or by the TPI access layer, depending on the type of
instruction issued.
The TPI access layer controls the character transfer direction on the TPI physical layer. It also handles
the recovery from the error state after exception.
The Control and Status Space (CSS) of the Tiny Programming Interface is allocated for control and status
registers in the TPI access Layer. The CSS consist of registers directly involved in the operation of the
TPI itself. These register are accessible using the SLDCS and SSTCS instructions.
The access layer can also access the data space, either directly or indirectly using the Pointer Register
(PR) as the address pointer. The data space is accessible using the SLD, SST, SIN and SOUT
instructions. The address pointer can be stored in the Pointer Register using the SLDPR instruction.
21.4.11.1. Message format
Each message comprises an instruction followed by one or more byte operands. The instruction is always
sent by the external programmer. Depending on the instruction all the following operands are sent either
by the external programmer or by the TPI.
The messages can be categorized in two types based on the instruction, as follows:
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•
•
Write messages. A write message is a request to write data. The write message is sent entirely by
the external programmer. This message type is used with the SSTCS, SST, STPR, SOUT and
SKEY instructions.
Read messages. A read message is a request to read data. The TPI reacts to the request by
sending the byte operands. This message type is used with the SLDCS, SLD and SIN instructions.
All the instructions except the SKEY instruction require the instruction to be followed by one byte
operand. The SKEY instruction requires 8 byte operands. For more information, see the TPI instruction
set.
21.4.11.2. Exception Handling and Synchronisation
Several situations are considered exceptions from normal operation of the TPI. When the TPI physical
layer is in receive mode, these exceptions are:
•
•
•
The TPI physical layer detects a parity error.
The TPI physical layer detects a frame error.
The TPI physical layer recognizes a BREAK character.
When the TPI physical layer is in transmit mode, the possible exceptions are:
The TPI physical layer detects a data collision.
•
All these exceptions are signalized to the TPI access layer. The access layer responds to an exception by
aborting any on-going operation and enters the error state. The access layer will stay in the error state
until a BREAK character has been received, after which it is taken back to its default state. As a
consequence, the external programmer can always synchronize the protocol by simply transmitting two
successive BREAK characters.
21.5. Instruction Set
The TPI has a compact instruction set that is used to access the TPI Control and Status Space (CSS)
and the data space. The instructions allow the external programmer to access the TPI, the NVM
Controller and the NVM memories. All instructions except SKEY require one byte operand following the
instruction. The SKEY instruction is followed by 8 data bytes. All instructions are byte-sized.
Table 21-1.ꢀInstruction Set Summary
Mnemonic Operand
Description
Operation
SLD
SLD
data, PR
Serial LoaD from data space using indirect addressing
data ← DS[PR]
data, PR+
Serial LoaD from data space using indirect addressing and
post-increment
data ← DS[PR]
PR ← PR+1
SST
SST
PR, data
Serial STore to data space using indirect addressing
DS[PR] ← data
PR+, data
Serial STore to data space using indirect addressing and
post-increment
DS[PR] ← data
PR ← PR+1
SSTPR
SIN
PR, a
Serial STore to Pointer Register using direct addressing
Serial IN from data space
PR[a] ← data
data ← I/O[a]
I/O[a] ← data
data, a
a, data
SOUT
Serial OUT to data space
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Mnemonic Operand
Description
Operation
SLDCS
SSTCS
SKEY
data, a
Serial LoaD from Control and Status space using direct
addressing
data ← CSS[a]
a, data
Serial STore to Control and Status space using direct
addressing
CSS[a] ← data
Key ← {8{data}}
Key, {8{data}} Serial KEY
21.5.1. SLD - Serial LoaD from data space using indirect addressing
The SLD instruction uses indirect addressing to load data from the data space to the TPI physical layer
shift-register for serial read-out. The data space location is pointed by the Pointer Register (PR), where
the address must have been stored before data is accessed. The Pointer Register is either left
unchanged by the operation, or post-incremented.
Table 21-2.ꢀThe Serial Load from Data Space (SLD) Instruction
Operation
Opcode
Remarks
Register
data ← DS[PR]
data ← DS[PR]
0010 0000
0010 0100
PR ← PR
Unchanged
Post increment
PR ← PR + 1
21.5.2. SST - Serial STore to data space using indirect addressing
The SST instruction uses indirect addressing to store into data space the byte that is shifted into the
physical layer shift register. The data space location is pointed by the Pointer Register (PR), where the
address must have been stored before the operation. The Pointer Register can be either left unchanged
by the operation, or it can be post-incremented.
Table 21-3.ꢀThe Serial Store to Data Space (SST) Instruction
Operation
Opcode
Remarks
Register
DS[PR] ← data
DS[PR] ← data
0110 0000
0110 0000
PR ← PR
Unchanged
Post increment
PR ← PR + 1
21.5.3. SSTPR - Serial STore to Pointer Register
The SSTPR instruction stores the data byte that is shifted into the physical layer shift register to the
Pointer Register (PR). The address bit of the instruction specifies which byte of the Pointer Register is
accessed.
Table 21-4.ꢀThe Serial Store to Pointer Register (SSTPR) Instruction
Operation
Opcode
Remarks
PR[a] ← data
0110 100a
Bit ‘a’ addresses Pointer Register byte
21.5.4. SIN - Serial IN from i/o space using direct addressing
The SIN instruction loads data byte from the I/O space to the shift register of the physical layer for serial
read-out. The instuction uses direct addressing, the address consisting of the 6 address bits of the
instruction.
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Table 21-5.ꢀThe Serial IN from i/o space (SIN) Instruction
Operation
Opcode
Remarks
data ← I/O[a]
0aa1 aaaa
Bits marked ‘a’ form the direct, 6-bit address
21.5.5. SOUT - Serial OUT to i/o space using direct addressing
The SOUT instruction stores the data byte that is shifted into the physical layer shift register to the I/O
space. The instruction uses direct addressing, the address consisting of the 6 address bits of the
instruction.
Table 21-6.ꢀThe Serial OUT to i/o space (SOUT) Instruction
Operation
Opcode
Remarks
I/O[a] ← data
1aa1 aaaa
Bits marked ‘a’ form the direct, 6-bit address
21.5.6. SLDCS - Serial LoaD data from Control and Status space using direct addressing
The SLDCS instruction loads data byte from the TPI Control and Status Space to the TPI physical layer
shift register for serial read-out. The SLDCS instruction uses direct addressing, the direct address
consisting of the 4 address bits of the instruction.
Table 21-7.ꢀThe Serial Load Data from Control and Status space (SLDCS) Instruction
Operation
Opcode
Remarks
data ← CSS[a]
1000 aaaa
Bits marked ‘a’ form the direct, 4-bit address
21.5.7. SSTCS - Serial STore data to Control and Status space using direct addressing
The SSTCS instruction stores the data byte that is shifted into the TPI physical layer shift register to the
TPI Control and Status Space. The SSTCS instruction uses direct addressing, the direct address
consisting of the 4 address bits of the instruction.
Table 21-8.ꢀThe Serial STore data to Control and Status space (SSTCS) Instruction
Operation
Opcode
Remarks
CSS[a] ← data
1100 aaaa
Bits marked ‘a’ form the direct, 4-bit address
21.5.8. SKEY - Serial KEY signaling
The SKEY instruction is used to signal the activation key that enables NVM programming. The SKEY
instruction is followed by the 8 data bytes that includes the activation key.
Table 21-9.ꢀThe Serial KEY signaling (SKEY) Instruction
Operation
Opcode
Remarks
Key ← {8[data}}
1110 0000
Data bytes follow after instruction
21.6. Accessing the Non-Volatile Memory Controller
By default, NVM programming is not enabled. In order to access the NVM Controller and be able to
program the non-volatile memories, a unique key must be sent using the SKEY instruction.
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Table 21-10.ꢀEnable Key for Non-Volatile Memory Programming
Key
Value
NVM Program Enable
0x1289AB45CDD888FF
After the key has been given, the Non-Volatile Memory Enable (NVMEN) bit in the TPI Status Register
(TPISR) must be polled until the Non-Volatile memory has been enabled.
NVM programming is disabled by writing a logical zero to the NVMEN bit in TPISR.
21.7. Control and Status Space Register Descriptions
The control and status registers of the Tiny Programming Interface are mapped in the Control and Status
Space (CSS) of the interface. These registers are not part of the I/O register map and are accessible via
SLDCS and SSTCS instructions, only. The control and status registers are directly involved in
configuration and status monitoring of the TPI.
Table 21-11.ꢀSummary of Control and Status Registers
Offset
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x0F
0x0E
TPIIR
Tiny Programming Interface Identification Code
Reserved
-
-
-
-
-
-
-
-
...
0x03
0x02
0x01
0x00
TPIPCR
Reserved
TPISR
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
GT2
GT1
-
GT0
-
-
-
-
NVMEN
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21.7.1. Tiny Programming Interface Identification Register
Name:ꢀ TPIIR
Offset:ꢀ
Reset:ꢀ 0x00
Property: CSS: 0x0F
ꢀ
Bit
7
6
5
4
3
2
1
0
TPIIC[7:0]
Access
Reset
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 – TPIIC[7:0]:ꢀTiny Programming Interface Identification Code
These bits give the identification code for the Tiny Programming Interface. The code can be used be the
external programmer to identify the TPI.
Table 21-12.ꢀIdentification Code for Tiny Programming Interface
Code
Value
Interface Identification
0x80
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21.7.2. Tiny Programming Interface Physical Layer Control Register
Name:ꢀ TPIPCR
Offset:ꢀ
Reset:ꢀ 0x00
Property: CSS: 0x02
ꢀ
Bit
7
6
5
4
3
2
1
0
GT2
R/W
0
GT1
R/W
0
GT0
R/W
0
Access
Reset
Bits 2:0 – GTn:ꢀGuard Time [n=2:0]
These bits specify the number of additional IDLE bits that are inserted to the idle time when changing
from reception mode to transmission mode. Additional delays are not inserted when changing from
transmission mode to reception.
The total idle time when changing from reception to transmission mode is Guard Time plus two IDLE bits.
Table 21-13.ꢀIdentification Code for Tiny Programming Interface
GT2
0
GT1
0
GT0
0
Guard Time (Number of IDLE bits)
+128 (default value)
0
0
1
+64
+32
+16
+8
0
1
0
0
1
1
1
0
0
1
0
1
+4
1
1
0
+2
1
1
1
+0
The default Guard Time is 128 IDLE bits. To speed up the communication, the Guard Time should be set
to the shortest safe value.
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21.7.3. Tiny Programming Interface Status Register
Name:ꢀ TPISR
Offset:ꢀ
Reset:ꢀ 0x00
Property: CSS: 0x00
ꢀ
Bit
7
6
5
4
3
2
1
NVMEN
R/W
0
0
Access
Reset
Bit 1 – NVMEN:ꢀNon-Volatile Memory Programming Enabled
NVM programming is enabled when this bit is set. The external programmer can poll this bit to verify the
interface has been successfully enabled.
NVM programming is disabled by writing this bit to zero.
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22.
Electrical Characteristics
22.1. Absolute Maximum Ratings*
Operating Temperature
Storage Temperature
-55°C to +125°C
-65°C to +150°C
-0.5V to VCC+0.5V
Voltage on any Pin except RESET
with respect to Ground
Voltage on RESET with respect to Ground
Maximum Operating Voltage
DC Current per I/O Pin
-0.5V to +13.0V
6.0V
40.0 mA
DC Current VCC and GND Pins
200.0 mA
Note:ꢀ 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 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.
22.2. DC Characteristics
Table 22-1.ꢀ Common DC characteristics TA = -40°C to 125°C, VCC = 1.8V to 5.5V (unless otherwise noted)
Symbol
Parameter Condition
Min.
-0.5
-0.5
Typ.(1)
Max.
Units
(2)
(2)
VIL
Input Low
Voltage,
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.2VCC
0.3VCC
V
except
XTAL1 and
RESET pin
(3)
(3)
VIH
Input High VCC = 1.8V - 2.4V
0.7VCC
0.6VCC
VCC + 0.5
VCC + 0.5
V
Voltage,
VCC = 2.4V - 5.5V
except
XTAL1 and
RESET
pins
(2)
VIL1
VIH1
VIL2
Input Low
Voltage,
CLKI pin
VCC = 1.8V - 5.5V
-0.5
0.1VCC
V
V
V
(3)
(3)
Input High VCC = 1.8V - 2.4V
Voltage,CL
VCC = 2.4V - 5.5V
KI pin
0.8VCC
0.7VCC
VCC + 0.5
VCC + 0.5
(2)
Input Low
Voltage,
VCC = 1.8V - 5.5V
-0.5
0.1VCC
RESET pin
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Symbol
Parameter Condition
Min.
Typ.(1)
Max.
Units
(3)
VIH2
Input High VCC = 1.8V - 5.5V
Voltage,
0.9VCC
VCC + 0.5
V
RESET pin
(2)
VIL3
VIH3
VOL
Input Low
Voltage,
RESET pin
as I/O
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
-0.5
-0.5
0.2VCC
V
V
V
(2)
0.3VCC
(3)
(3)
Input High VCC = 1.8V - 2.4V
Voltage,
RESET pin
VCC = 2.4V - 5.5V
as I/O
0.7VCC
0.6VCC
VCC + 0.5
VCC + 0.5
0.6
Output Low
Voltage(4)
except
RESET
pin(6)
IOL = 10mA, VCC = 5V
0.5
IOL = 5mA, VCC = 3V
VOH
Output
High
Voltage(5)
except
Reset pin(6)
4.3
2.5
V
IOH = 10mA, VCC = 5V
IOH = 5mA, VCC = 3V
IIL
Input
VCC = 5.5V, pin low
(absolute value)
<0.05
<0.05
1
1
μA
μA
Leakage
Current I/O
Pin
IIH
Input
VCC = 5.5V, pin high
(absolute value)
Leakage
Current I/O
Pin
RRST
Reset Pull- VCC = 5.5V, input low
up Resistor
30
20
60
50
kΩ
kΩ
RPU
I/O Pin
Pull-up
Resistor
VCC = 5.5V, input low
IACLK
Analog
Comparato
r
-50
50
nA
VCC=5V
,
Input
Vin = VCC/2
Leakage
Current
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Symbol
Parameter Condition
Min.
Typ.(1)
0.2
Max.
0.5
1.2
4
Units
mA
mA
mA
mA
mA
mA
μA
ICC
Power
Active 1MHz, VCC = 2V
Supply
Active 4MHz, VCC = 3V
Active 8MHz, VCC = 5V
Idle 1MHz, VCC = 2V
Idle 4MHz, VCC = 3V
Idle 8MHz, VCC = 5V
WDT enabled, TA=105°
1.1
Current(7)
3.2
0.03
0.2
0.2
0.5
1.5
10
0.9
Power-
down
mode(8)
5.5
Vcc =3V
C
TA=125°
C
5.5
16
2
μA
μA
μA
WDT disabled, TA=105°
Vcc =3V
0.11
0.11
C
TA=125°
C
8
Note:ꢀ
1. Typical values at 25°C, maximum values unless otherwise noted.
2. “Max” means the highest value where the pin is guaranteed to be read as low.
3. “Min” means the lowest value where the pin is guaranteed to be read as high.
4. Although each I/O port can sink more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC
=
3V) under steady state conditions (non-transient), the sum of all IOL (for all ports) should not exceed
60 mA. If IOL exceeds the test conditions, VOL may exceed the related specification. Pins are not
guaranteed to sink current greater than the listed test condition.
5. Although each I/O port can source more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC
= 3V) under steady state conditions (non-transient), the sum of all IOH (for all ports) should not
exceed 60 mA. 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.
6. The RESET pin must tolerate high voltages when entering and operating in programming modes
and, as a consequence, has a weak drive strength as compared to regular I/O pins.
7. Values are with external clock using methods described in Minimizing Power Consumption. Power
Reduction is enabled (PRR = 0xFF) and there is no I/O drive.
8. BOD Disabled.
22.3. Speed
The maximum operating frequency of the device depends on VCC . The relationship between maximum
frequency vs. VCC is linear between 1.8V < VCC < 4.5V.
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Figure 22-1.ꢀMaximum Frequency vs. VCC
12 MHz
8 MHz
4 MHz
1.8V
2.7V
4.5V
5.5V
22.4. Clock Characteristics
22.4.1. Accuracy of Calibrated Internal Oscillator
It is possible to manually calibrate the internal oscillator to be more accurate than default factory
calibration. Note that the oscillator frequency depends on temperature and voltage. .
Table 22-2.ꢀCalibration Accuracy of Internal RC Oscillator
Calibration Target Frequency
Method
VCC
Temperature
Accuracy at given
Voltage &
Temperature
Factory
8.0MHz
2.7 - 4.0V
0°C - 85°C
±2%
Calibration
User
Fixed frequency within: Fixed voltage
Fixed temp. within: ±1%(1)
-40°C - 85°C
Calibration 7.3 - 8.1MHz
within:
1.7 - 5.5V
Note:ꢀ
1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage).
22.4.2. External Clock Drive
Figure 22-2.ꢀExternal Clock Drive Waveform
V
IH1
V
IL1
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Table 22-3.ꢀExternal Clock Drive Characteristics
Symbol Parameter
VCC = 1.8 - 5.5V VCC = 2.7 - 5.5V VCC = 4.5 - 5.5V Units
Min.
Max.
Min.
0
Max.
Min.
0
Max.
1/tCLCL Clock Frequency
0
4
8
12
MHz
ns
tCLCL
tCHCX
tCLCX
tCLCH
tCHCL
Clock Period
High Time
Low Time
Rise Time
Fall Time
250
100
100
125
50
83
33
33
ns
50
ns
2.0
2.0
2
1
1
2
0.6
0.6
2
μs
μs
%
ΔtCLCL Change in period from one clock
cycle to the next
22.5. System and Reset Characteristics
Table 22-4.ꢀReset, VLM, and Internal Voltage Characteristics
Symbol
Parameter
Condition
Min(1)
Typ(1)
Max(1)
Units
VRST
RESET Pin Threshold
Voltage
0.2 VCC
0.9VCC
V
VBG
Internal bandgap voltage
VCC = 1.8V to
5.5V
1.0
1.1
1.2
V
tRST
Minimum pulse width on
RESET Pin
2100
ns
VCC = 1.8V
VCC = 3V
VCC = 5V
700
400
64
ns
ns
ms
tTOUT
Time-out after reset
128
Note:ꢀ
1. Values are guidelines, only
22.5.1. Power-On Reset
Table 22-5.ꢀCharacteristics of Enhanced Power-On Reset. TA = -40 to 125°C
Symbol
VPOR
Parameter
Min(1)
1.1
Typ(1)
1.4
Max(1)
1.6
Units
V
Release threshold of power-on reset (2)
Activation threshold of power-on reset (3)
Power-On Slope Rate
VPOA
0.6
1.2
1.6
V
SRON
0.01
V/ms
Note:ꢀ
1. Values are guidelines, only
2. Threshold where device is released from reset when voltage is rising
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3. The Power-on Reset will not work unless the supply voltage has been below VPOT(falling)
22.5.2. VCC Level Monitor
Table 22-6.ꢀVoltage Level Monitor Thresholds
Parameter
Min
1.1
1.4
2.0
3.2
Typ (1)
1.4
Max
1.6
1.8
2.7
4.5
Units
Trigger level VLM1L
V
Trigger level VLM1H
Trigger level VLM2
1.6
2.5
Trigger level VLM3
3.7
Settling time VMLM2,VLM3 (VLM1H,VLM1L)
5 (50)
µs
Note:ꢀ
1. Typical values at room temperature
22.6. Analog Comparator Characteristics
Table 22-7.ꢀAnalog Comparator Characteristics, TA = -40°C to 125°C
Symbol Parameter
VAIO Input Offset Voltage
ILAC
tAPD
Condition
Min Typ Max Units
VCC = 5V, VIN = VCC / 2
VCC = 5V, VIN = VCC / 2
VCC = 2.7V
10 40
50
mV
nA
ns
Input Leakage Current
-50
*
Analog Propagation Delay
150
(from saturation to 100mV overdrive)
VCC = 4.0V
185
Analog Propagation Delay
VCC = 2.7V
135
(from step change of 100mV)
VCC = 4.0V
160
tDPD
Digital Propagation Delay
VCC = 1.8V - 5.5V
1
2
CLK
Note:ꢀ *: 15ns delay IP to pad removed
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22.7. ADC Characteristics
Table 22-8.ꢀADC Characteristics. T = -40°C to 125°C VCC = 1.8V - 5.5V
Symbol Parameter
Condition
Min Typ Max Units
Resolution
10
Bits
Absolute accuracy
VREF = VCC = 4.3V,
2
LSB
(Including INL, DNL, and
Quantization, Gain and
Offset Errors)
ADC clock = 200 kHz
VREF = VCC = 4.3V,
ADC clock = 1 MHz
3
VREF = VCC = 4.3V, ADC clock = 200
kHz
1.5
LSB
Noise Reduction Mode
VREF = VCC = 4.3V, ADC clock = 1
MHz
2.5
Noise Reduction Mode
INL
Integral Non-Linearity
(Accuracy after Offset and ADC clock = 200 kHz
Gain Calibration)
VREF = VCC = 4.0V,
0.51 0.68 0.88 LSB
0.39 0.62 0.92
VREF = VCC = 4.0V,
ADC clock = 1 MHz
DNL
Differential Non-linearity
Gain Error
VREF = VCC = 4.0V, ADC clock = 200
kHz
0.42 0.49 0.73 LSB
0.22 0.48 0.55
VREF = VCC = 4.0V,
ADC clock = 1 MHz
VREF = VCC = 4.0V, ADC clock = 200
kHz
-7.2 -4
-1
LSB
Int VREF = 1.1V, VCC = 4.0V, ADC clock -41.3 -13.3 -1.9
= 200 kHz
Int VREF = 2.2V, VCC = 4.0V, ADC clock -38.3 -8.7 3.1
= 200 kHz
Int VREF = 4.3V, VCC = 4.0V, ADC clock -80.4 -3.2 9.9
= 200 kHz
Offset Error
VREF = VCC = 4.0V, ADC clock = 200
kHz
3.0
5.1
8
LSB
Int VREF = 1.1V, VCC = 4.0V, ADC clock -54 9.1
= 200 kHz
2
Int VREF = 2.2V, VCC = 4.0V, ADC clock 2
= 200 kHz
5.4
11
5.4
Int VREF = 4.3V, VCC = 4.0V, ADC clock 1
= 200 kHz
3.4
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Symbol Parameter
Conversion Time
Condition
Min Typ Max Units
Single Conversion
13
260 µs
Clock Frequency
50
1000 kHz
VIN
Input Voltage
GND
VREF
V
Input Bandwidth
38.5
100
kHz
MΩ
RAIN
Analog Input Resistance
ADC Conversion Output
0
1023 LSB
22.8. Serial Programming Characteristics
Figure 22-3.ꢀSerial Programming Timing
Receive Mode
Transmit Mode
TPIDATA
t
t
t
CLOV
IVCH
CHIX
TPICLK
t
t
CHCL
CLCH
t
CLCL
Table 22-9.ꢀSerial Programming Characteristics, TA = -40°C to 125°C, VCC = 5V ± 5% (Unless Otherwise
Noted)
Symbol
1/tCLCL
tCLCL
Parameter
Min
Typ
Max
Units
MHz
ns
Clock Frequency
2
Clock Period
500
200
200
50
tCLCH
tCHCH
tIVCH
Clock Low Pulse Width
Clock High Pulse Width
Data Input to Clock High Setup Time
Data Input Hold Time After Clock High
Data Output Valid After Clock Low Time
ns
ns
ns
tCHIX
100
ns
tCLOV
200
ns
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23.
Typical Characteristics
The data contained in this section is largely based on simulations and characterization of similar devices
in the same process and design methods. Thus, the data should be treated as indications of how the part
will behave.
The following charts show typical behavior. These figures are not tested during manufacturing. During
characterisation devices are operated at frequencies higher than test limits but they are not guaranteed to
function properly at frequencies higher than the ordering code indicates.
All current consumption measurements are performed with all I/O pins configured as inputs and with
internal pull-ups enabled. 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.
A sine wave generator with rail-to-rail output is used as clock source but current consumption in Power-
Down mode is independent of clock selection. 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.
The current drawn from pins with a capacitive load may be estimated (for one pin) as follows:
I
≃ V × C × f
CC L
CP
SW
where VCC = operating voltage, CL = load capacitance and fSW = average switching frequency of I/O pin.
23.1. Active Supply Current
Figure 23-1.ꢀActive Supply Current vs. Low Frequency (0.1 - 1.0 MHz)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
5.5V
5V
4.5V
4V
3.3V
2.7V
1.8V
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency [MHz]
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Figure 23-2.ꢀActive Supply Current vs. frequency (1 - 12 MHz)
6
5
4
3
2
1
0
5.5V
5V
4.5V
4V
3.3V
2.7V
1.8V
0
2
4
6
8
10
12
Frequency [MHz]
Figure 23-3.ꢀActive Supply Current vs. VCC (Internal Oscillator, 8 MHz)
5
4.5
4
3.5
3
125°C
105°C
85°C
25°C
0°C
2.5
2
1.5
1
0.5
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
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Figure 23-4.ꢀActive Supply Current vs. VCC (Internal Oscillator, 1 MHz)
1.2
1
0.8
0.6
0.4
0.2
0
125°C
105°C
85°C
25°C
0°C
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc [V]
Figure 23-5.ꢀActive Supply Current vs. VCC (Internal Oscillator, 128 kHz)
0.14
0.12
0.1
125°C
0.08
0.06
0.04
0.02
0
105°C
85°C
25°C
0°C
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc [V]
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23.2. Idle Supply Current
Figure 23-6.ꢀIdle Supply Current vs. Low Frequency (0.1 - 1.0 MHz)
0.14
0.12
0.1
5.5V
5V
0.08
0.06
0.04
0.02
0
4.5V
4V
3.3V
2.7V
1.8V
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency[MHz]
Figure 23-7.ꢀIdle Supply Current vs. Frequency (1 - 12 MHz)
1.5
1.4
1.3
1.2
1.1
1
5.5V
5V
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
4.5V
4V
3.3V
2.7V
1.8V
0
2
4
6
8
10
12
Frequency[MHz]
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Figure 23-8.ꢀIdle Supply Current vs. VCC (Internal Oscillator, 8 MHz)
1.2
1
0.8
0.6
0.4
0.2
0
125°C
105°C
85°C
25°C
0°C
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Figure 23-9.ꢀIdle Supply Current vs. VCC (Internal Oscillator, 1 MHz)
0.4
0.35
0.3
0.25
0.2
125°C
105°C
85°C
25°C
0°C
0.15
0.1
0.05
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
23.3. Supply Current of I/O Modules
Tables and formulas below can be used to calculate additional current consumption for the different I/O
modules in Active and Idle mode. Enabling and disabling of I/O modules is controlled by the Power
Reduction Register. See Power Reduction Register for details.
Table 23-1.ꢀAdditional Current Consumption for the different I/O modules (absolute values)
PRR bit
Typical numbers
VCC = 2V, f = 1MHz
6.6 µA
VCC = 3V, f = 4MHz
40.0 µA
VCC = 5V, f = 8MHz
153.0 µA
PRTIM0
PRADC
29.6 µA
88.3 µA
333.3 µA
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The table below can be used for calculating typical current consumption for other supply voltages and
frequencies than those mentioned in the table above.
Table 23-2.ꢀAdditional Current Consumption (percentage) in Active and Idle mode
PRR bit Current consumption additional to active
mode with external clock
Current consumption additional to idle
mode with external clock
PRTIM0 2.3 %
PRADC 6.7 %
10.4 %
28.8 %
23.4. Power-down Supply Current
Figure 23-10.ꢀPower-down Supply Current vs. VCC (Watchdog Timer Disabled)
3
2.5
2
125°C
105°C
85°C
25°C
0°C
1.5
1
0.5
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc [V]
Figure 23-11.ꢀPower-down Supply Current vs. VCC (Watchdog Timer Enabled)
14
12
10
8
125°C
105°C
85°C
25°C
0°C
6
4
2
-40°C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc [V]
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23.5. Pin Driver Strength
Figure 23-12.ꢀI/O Pin Output Voltage vs. Sink Current (VCC = 1.8V)
1.4
1.2
1
125°C
105°C
85°C
25°C
0°C
0.8
0.6
0.4
0.2
0
-40°C
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Iol[mA]
Figure 23-13.ꢀI/O Pin Output Voltage vs. Sink Current (VCC = 3V)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
125°C
105°C
85°C
25°C
0°C
-40°C
0
1
2
3
4
5
6
7
8
9
10
Iol[mA]
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Figure 23-14.ꢀI/O pin Output Voltage vs. Sink Current (VCC = 5V)
1.2
1
0.8
0.6
0.4
0.2
0
125°C
105°C
85°C
25°C
0°C
-40°C
0
2
4
6
8
10
12
14
16
18
20
Iol[mA]
Figure 23-15.ꢀI/O Pin Output Voltage vs. Source Current (VCC = 1.8V)
2
1.8
1.6
1.4
1.2
1
125°C
105°C
85°C
25°C
0°C
0.8
0.6
0.4
0.2
0
-40°C
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Ioh[mA]
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Figure 23-16.ꢀI/O Pin Output Voltage vs. Source Current (VCC = 3V)
3.5
3
2.5
2
125°C
105°C
85°C
25°C
0°C
1.5
1
0.5
0
-40°C
0
1
2
3
4
5
6
7
8
9
10
Ioh[mA]
Figure 23-17.ꢀI/O Pin output Voltage vs. Source Current (VCC = 5V)
5.1
4.9
4.7
4.5
4.3
4.1
3.9
3.7
3.5
125°C
105°C
85°C
25°C
0°C
-40°C
0
2
4
6
8
10
12
14
16
18
20
Ioh[mA]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
226
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-18.ꢀReset Pin as I/O, Output Voltage vs. Sink Current
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
5V
3V
1.8V
0
0.5
1
1.5
2
2.5
3
3.5
4
IOL [mA]
Figure 23-19.ꢀReset Pin as I/O, Output Voltage vs. Source Current
5
4
3
2
1
0
5V
3V
1.8V
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
IOH [mA]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
227
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
23.6. Pin Threshold and Hysteresis
Figure 23-20.ꢀI/O Pin Input Threshold Voltage vs. VCC (VIH, IO Pin Read as ‘1’)
3
2.5
2
125°C
105°C
85°C
25°C
0°C
1.5
1
0.5
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
Vcc[V]
Figure 23-21.ꢀI/O Pin Input threshold Voltage vs. VCC (VIL, IO Pin Read as ‘0’)
3
2.5
2
125°C
105°C
85°C
25°C
0°C
1.5
1
0.5
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
228
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-22.ꢀI/O Pin Input Hysteresis vs. VCC
0.6
0.5
0.4
0.3
0.2
0.1
0
125°C
105°C
85°C
25°C
0°C
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Figure 23-23.ꢀReset Pin as I/O, Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as ‘1’)
3.5
3
2.5
2
125°C
105°C
85°C
25°C
0°C
1.5
1
0.5
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
229
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-24.ꢀReset Pin as I/O, Input Threshold Voltage vs. VCC (VIL, I/O pin Read as ‘0’)
2.5
2
1.5
1
125°C
105°C
85°C
25°C
0°C
0.5
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Figure 23-25.ꢀReset Input Hysteresis vs. VCC (Reset Pin Used as I/O)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
125°C
105°C
85°C
25°C
0°C
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
230
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-26.ꢀReset Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as ‘1’)
2.5
2
1.5
1
125°C
105°C
85°C
25°C
0°C
0.5
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Figure 23-27.ꢀReset Input Threshold Voltage vs. VCC (VIL, I/O pin Read as ‘0’)
2.5
2
1.5
1
125°C
105°C
85°C
25°C
0°C
0.5
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
231
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-28.ꢀReset Pin, Input Hysteresis vs. VCC
0.6
0.5
0.4
0.3
0.2
0.1
0
125°C
105°C
85°C
25°C
0°C
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
23.7. Analog Comparator Offset
Figure 23-29.ꢀAnalog Comparator Offset
3
125°C
1
-1
105°C
85°C
-3
25°C
-5
-7
-9
-40°C
-11
0
1
2
3
4
5
VIN [V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
232
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
23.8. Pin Pull-up
Figure 23-30.ꢀI/O pin Pull-up Resistor Current vs. Input Voltage (VCC = 1.8V)
60
50
40
30
20
10
0
125°C
105°C
85°C
25°C
0°C
-40°C
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
VOP [V]
Figure 23-31.ꢀI/O Pin Pull-up Resistor Current vs. input Voltage (VCC = 2.7V)
90
80
70
60
50
40
30
20
10
0
125°C
105°C
85°C
25°C
0°C
-40°C
0
0.5
1
1.5
2
2.5
3
VOP [V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
233
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-32.ꢀI/O pin Pull-up Resistor Current vs. Input Voltage (VCC = 5V)
160
140
120
100
80
125°C
105°C
85°C
25°C
0°C
60
40
20
-40°C
0
0
1
2
3
4
5
6
VOP [V]
Figure 23-33.ꢀReset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 1.8V)
40
35
30
25
20
15
10
5
125°C
105°C
85°C
25°C
0°C
-40°C
0
0
0.2
0.4
0.6
0.8
VRESET [V]
1
1.2
1.4
1.6
1.8
Atmel ATtiny102 / ATtiny104 [DATASHEET]
234
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-34.ꢀReset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
70
60
50
40
30
20
10
0
125°C
105°C
85°C
25°C
0°C
-40°C
0
0.5
1
1.5
2
2.5
3
VRESET [V]
Figure 23-35.ꢀReset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
80
70
60
50
40
30
20
10
0
125°C
105°C
85°C
25°C
0°C
-40°C
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
5
VRESET [V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
235
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
23.9. Internal Oscillator Speed
Figure 23-36.ꢀWatchdog Oscillator Frequency vs. VCC
118
116
114
112
110
108
106
104
102
125°C
105°C
85°C
25°C
0°C
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Figure 23-37.ꢀWatchdog Oscillator Frequency vs. Temperature
118
116
114
112
110
108
106
104
102
5.5V
5V
4.5V
4V
3.3V
2.7V
1.8V
-60
-40
-20
0
20
40
60
80
100
120
140
Temp [°C]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
236
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-38.ꢀCalibrated Oscillator Frequency vs. VCC
8.5
8.4
8.3
125°C
105°C
85°C
25°C
0°C
8.2
8.1
8
7.9
-40°C
7.8
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Figure 23-39.ꢀCalibrated Oscillator Frequency vs. Temperature
8.5
8.4
8.3
8.2
8.1
8
5.5V
5V
4.5V
4V
3.3V
2.7V
1.8V
7.9
7.8
-45
-25
-5
15
35
55
75
95
115
Temperature [°C]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
237
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-40.ꢀCalibrated Oscillator Frequency vs. OSCCAL Value
18
16
14
12
10
8
125°C
105°C
85°C
25°C
0°C
6
4
2
-40°C
0
0
15
30
45
60
75
90
105 120 135 150 165 180 195 210 225 240 255
OscCal[x1]
23.10. VLM Thresholds
Figure 23-41.ꢀVLM1L Threshold of VCC Level Monitor
1.44
1.43
1.42
1.41
1.4
1.39
1.38
1.37
1.36
1.35
1.34
1.33
RISING
FALLING
-60
-40
-20
0
20
40
60
80
100
120
140
Temp [°C]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
238
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-42.ꢀVLM1H Threshold of VCC Level Monitor
1.7
1.65
1.6
1.55
1.5
RISING
FALLING
1.45
-60
-40
-20
0
20
40
60
80
100
120
140
Temp [°C]
Figure 23-43.ꢀVLM2 Threshold of VCC Level Monitor
2.49
2.48
2.47
2.46
2.45
2.44
2.43
2.42
2.41
2.4
RISING
FALLING
2.39
-60
-40
-20
0
20
40
60
80
100
120
140
Temp [°C]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
239
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-44.ꢀVLM3 Threshold of VCC Level Monitor
3.95
3.9
3.85
3.8
3.75
3.7
RISING
3.65
3.6
FALLING
3.55
3.5
-60
-40
-20
0
20
40
60
80
100
120
140
Temp [°C]
23.11. Current Consumption of Peripheral Units
Figure 23-45.ꢀADC Current vs. VCC
0.45
0.4
0.35
0.3
0.25
0.2
85°C
25°C
0°C
0.15
0.1
-40°C
0.05
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
240
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-46.ꢀAnalog Comparator (AC) Current vs. VCC
45
40
35
30
25
20
15
10
5
125°C
105°C
85°C
25°C
0°C
-40°C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Figure 23-47.ꢀVCC Level Monitor Current vs. VCC
350
300
250
200
150
100
50
VLM2:0 = 100
VLM2:0 = 011
VLM2:0 = 010
VLM2:0 = 001
VLM2:0 = 000
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
241
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Figure 23-48.ꢀTemperature Dependence of VLM Current vs. VCC
0.4
0.35
0.3
0.25
0.2
85°C
25°C
0°C
0.15
0.1
-40°C
0.05
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc [V]
Figure 23-49.ꢀWatchdog Timer Current vs. VCC
12
10
8
125°C
105°C
85°C
25°C
0°C
6
4
2
-40°C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
242
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
23.12. Current Consumption in Reset and Reset Pulsewidth
Figure 23-50.ꢀReset Supply Current vs. VCC (0.1 - 1.0 MHz, excluding Current Through the Reset Pull-up)
800
700
600
5.5V
500
400
300
200
100
0
5V
4.5V
4V
3.3V
2.7V
1.8V
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency[MHz]
Note:ꢀ The default clock source for the device is always the internal 8 MHz oscillator. Hence, current
consumption in reset remains unaffected by external clock signals.
Figure 23-51.ꢀMinimum Reset Pulse Width vs. VCC
2500
2000
1500
125°C
105°C
85°C
25°C
0°C
1000
500
0
-40°C
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc[V]
Atmel ATtiny102 / ATtiny104 [DATASHEET]
243
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
24.
Register Summary
Offset
Name
Bit Pos.
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0A
0x0B
PINA
DDRA
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
15:8
7:0
PINA7
DDRA7
PORTA7
PUEA7
PINA6
DDRA6
PORTA6
PUEA6
PINA5
DDRA5
PORTA5
PUEA5
PINA4
DDRA4
PORTA4
PUEA4
PINA3
DDRA3
PORTA3
PUEA3
PINB3
PINA2
DDRA2
PORTA2
PUEA2
PINB2
PINA1
DDRA1
PORTA1
PUEA1
PINB1
PINA0
DDRA0
PORTA0
PUEA0
PINB0
PORTA
PUEA
PINB
DDRB
DDRB3
PORTB3
PUEB3
DDRB2
PORTB2
PUEB2
DDRB1
PORTB1
PUEB1
DDRB0
PORTB0
PUEB0
PORTB
PUEB
UDR0
TXB / RXB[7:0]
UBRR0[7:0]
UBRR0L and
UBRR0H
UCSR0D
UBRR0[11:8]
RXSIE
RXS
SFDE
UCSZ01 /
UDORD0
UCSZ02
UPE0
UCSZ00 /
UCPHA0
RXB80
U2X0
0x0C
UCSR0C
7:0
UMSEL01
UMSEL00
UPM01
UPM00
USBS0
UCPOL0
0x0D
0x0E
0x0F
0x10
0x11
0x12
0x13
0x14
0x15
0x16
0x17
0x18
0x19
0x1A
0x1B
0x1C
0x1D
0x1E
0x1F
0x20
...
UCSR0B
UCSR0A
PCMSK0
PCMSK1
PCIFR
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
7:0
RXCIE0
RXC0
TXCIE0
TXC0
UDRIE0
UDRE0
PCINT5
RXEN0
FE0
TXEN0
DOR0
TXB80
MPCM0
PCINT0
PCINT8
PCIF0
PCIE0
INT0
PCINT7
PCINT6
PCINT4
PCINT3
PCINT11
PCINT2
PCINT10
PCINT1
PCINT9
PCIF1
PCICR
PCIE1
EIMSK
EIFR
INTF0
EICRA
ISC0[1:0]
PORTCR
DIDR0
BBMB
BBMA
ADC7D
ADC7
ADC6D
ADC6
ADC5D
ADC5
ADC4D
ADC4
ADC3D
ADC3
ADC2D
ADC2
ADC1D
ADC0D
Reserved
7:0
15:8
7:0
7:0
7:0
7:0
7:0
ADC1
ADC9
ADC0
ADC8
ADCL and ADCH
ADMUX
ADCSRB
ADCSRA
ACSRB
REFS1
ADLAR
ADEN
REFS0
ADSC
ACBG
MUX2
ADTS2
ADPS2
MUX1
ADTS1
ADPS1
ACOE
ACIS1
MUX0
ADTS0
ADPS0
ACPMUX
ACIS0
ADATE
ACO
ADIF
ACI
ADIE
ACIE
ACSRA
ACD
ACIC
Reserved
0x21
0x22
0x23
0x24
0x25
0x26
0x27
0x28
0x29
7:0
15:8
7:0
ICR0[7:0]
ICR0L and ICR0H
ICR0[15:8]
OCR0B[7:0]
OCR0B[15:8]
OCR0A[7:0]
OCR0A[15:8]
TCNT0[7:0]
TCNT0[15:8]
OCR0BL and
OCR0BH
15:8
7:0
OCR0AL and
OCR0AH
15:8
7:0
TCNT0L and
TCNT0H
15:8
Atmel ATtiny102 / ATtiny104 [DATASHEET]
244
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
Offset
Name
Bit Pos.
0x2A
0x2B
0x2C
0x2D
0x2E
0x2F
0x30
0x31
0x32
0x33
0x34
0x35
0x36
0x37
0x38
0x39
0x3A
0x3B
0x3C
0x3D
0x3E
0x3F
...
TIFR0
TIMSK0
TCCR0C
TCCR0B
TCCR0A
GTCCR
Reserved
WDTCSR
NVMCSR
NVMCMD
VLMCSR
PRR
7:0
7:0
7:0
7:0
7:0
7:0
ICF0
OCF0B
OCF0A
TOV0
ICIE0
OCIE0B
OCIE0A
TOIE0
FOC0A
ICNC0
COM0A1
TSM
FOC0B
ICES0
WGM03
WGM02
WDE
CS0[2:0]
WGM01
REMAP
COM0A0
COM0B1
WDP3
COM0B0
WGM00
PSR
7:0
7:0
7:0
7:0
7:0
7:0
7:0
WDIF
WDIE
WDP2
WDP1
WDP0
NVMBSY
NVMCMD[5:0]
VLMF
VLMIE
VLM[2:0]
PRADC
PRUSART0
PRTIM0
CLKPSR
CLKMSR
Reserved
OSCCAL
SMCR
CLKPS[3:0]
CLKMS[1:0]
7:0
7:0
7:0
7:0
7:0
15:8
CAL[7:0]
SM[2:0]
SP2
SE
RSTFLR
CCP
WDRF
SP3
EXTRF
SP1
PORF
CCP[7:0]
SP6
SP5
SP4
SP0
SPL and SPH
Reserved
SREG
0x5E
0x5F
7:0
I
T
H
S
V
N
Z
C
24.1. Note
•
USART registers 0x08-0x0E are NOT bit accessible using SBI/CBI instructions
Atmel ATtiny102 / ATtiny104 [DATASHEET]
245
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
25.
Instruction Set Summary
Table 24-1.ꢀArithmetic and Logic Instructions
#Clocks
AVRrc
Mnemonic Operands
Description
Op
Flags
ADD
ADC
ADIW
SUB
SUBI
SBC
SBCI
SBIW
AND
ANDI
OR
Rd, Rr
Rd, Rr
Rd, K
Rd, Rr
Rd, K
Rd, Rr
Rd, K
Rd, K
Rd, Rr
Rd, K
Rd, Rr
Rd, K
Rd, Rr
Rd
Add without Carry
Add with Carry
Rd
Rd
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
Rd + Rr
Z,C,N,V,S,H
Z,C,N,V,S,H
Z,C,N,V,S
Z,C,N,V,S,H
Z,C,N,V,S,H
Z,C,N,V,S,H
Z,C,N,V,S,H
Z,C,N,V,S
Z,N,V,S
1
1
Rd + Rr + C
Rd + 1:Rd + K
Rd - Rr
Add Immediate to Word
Subtract without Carry
Subtract Immediate
Subtract with Carry
Subtract Immediate with Carry
Subtract Immediate from Word
Logical AND
Rd
N/A
1
Rd
Rd
Rd - K
1
Rd
Rd - Rr - C
Rd - K - C
Rd + 1:Rd - K
Rd • Rr
1
Rd
1
Rd + 1:Rd
Rd
N/A
1
Logical AND with Immediate
Logical OR
Rd
Rd • K
Z,N,V,S
1
Rd
Rd v Rr
Z,N,V,S
1
ORI
Logical OR with Immediate
Exclusive OR
Rd
Rd v K
Z,N,V,S
1
EOR
COM
NEG
SBR
CBR
INC
Rd
Rd ⊕ Rr
$FF - Rd
$00 - Rd
Rd v K
Z,N,V,S
1
One’s Complement
Two’s Complement
Set Bit(s) in Register
Clear Bit(s) in Register
Increment
Rd
Z,C,N,V,S
Z,C,N,V,S,H
Z,N,V,S
1
Rd
Rd
1
Rd,K
Rd,K
Rd
Rd
1
Rd
Rd • ($FFh - K)
Rd + 1
Z,N,V,S
1
Rd
Z,N,V,S
1
DEC
TST
Rd
Decrement
Rd
Rd - 1
Z,N,V,S
1
Rd
Test for Zero or Minus
Clear Register
Rd
Rd • Rd
Z,N,V,S
1
CLR
SER
Rd
Rd
Rd ⊕ Rd
$FF
Z,N,V,S
1
Rd
Set Register
Rd
None
1
Table 24-2.ꢀBranch Instructions
#Clocks
AVRrc
Mnemonic Operands
Description
Op
Flags
RJMP
IJMP
k
k
Relative Jump
PC
←
PC + k + 1
None
None
2
2
Indirect Jump to (Z)
PC(15:0)
←
←
Z
0
PC(21:16)
(1)
3
RCALL
ICALL
Relative Call Subroutine
Indirect Call to (Z)
PC
←
PC + k + 1
None
None
(1)
3
PC(15:0)
←
←
Z
0
PC(21:16)
(1)
6
RET
RETI
CPSE
CP
Subroutine Return
Interrupt Return
PC
PC
←
←
←
STACK
None
(1)
6
STACK
I
Rd,Rr
Rd,Rr
Rd,Rr
Rd,K
Compare, Skip if Equal
Compare
if (Rd = Rr) PC
Rd - Rr
PC + 2 or 3
None
1 / 2
Z,C,N,V,S,H
Z,C,N,V,S,H
Z,C,N,V,S,H
1
1
1
CPC
CPI
Compare with Carry
Compare with Immediate
Rd - Rr - C
Rd - K
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#Clocks
AVRrc
Mnemonic Operands
Description
Op
Flags
SBRC
SBRS
SBIC
Rr, b
Skip if Bit in Register Cleared
Skip if Bit in Register Set
Skip if Bit in I/O Register Cleared
Skip if Bit in I/O Register Set
Branch if Status Flag Set
Branch if Status Flag Cleared
Branch if Equal
if (Rr(b) = 0) PC
if (Rr(b) = 1) PC
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
PC + 2 or 3
PC + 2 or 3
PC + 2 or 3
PC + 2 or 3
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
PC + k + 1
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
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
1 / 2
1 / 2
1 / 2
Rr, b
A, b
A, b
s, k
s, k
k
if (I/O(A,b) = 0) PC
If (I/O(A,b) =1) PC
if (SREG(s) = 1) then PC
if (SREG(s) = 0) then PC
if (Z = 1) then PC
if (Z = 0) then PC
if (C = 1) then PC
if (C = 0) then PC
if (C = 0) then PC
if (C = 1) then PC
if (N = 1) then PC
if (N = 0) then PC
if (N ⊕ V= 0) then PC
if (N ⊕ V= 1) then PC
if (H = 1) then PC
if (H = 0) then PC
if (T = 1) then PC
if (T = 0) then PC
if (V = 1) then PC
if (V = 0) then PC
if (I = 1) then PC
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, 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
if (I = 0) then PC
Table 24-3.ꢀData Transfer Instructions
#Clocks
AVRrc
Mnemonic Operands
Description
Op
Flags
MOV
LDI
LDS
LD
Rd, Rr
Rd, K
Rd, k
Copy Register
Rd
Rd
Rd
Rd
←
←
←
←
Rr
K
None
None
None
None
None
1
1
Load Immediate
Load Direct from data space
Load Indirect
(k)
(X)
2
Rd, X
Rd, X+
1 / 2
2 / 3
LD
Load Indirect and Post-Increment
Rd
X
←
←
(X)
X + 1
LD
Rd, -X
Load Indirect and Pre-Decrement
X
←
←
X - 1
(X)
None
2 / 3
Rd
LD
LD
Rd, Y
Load Indirect
Rd
←
(Y)
None
None
1 / 2
2 / 3
Rd, Y+
Load Indirect and Post-Increment
Rd
Y
←
←
(Y)
Y + 1
LD
Rd, -Y
Load Indirect and Pre-Decrement
Y
←
←
Y - 1
(Y)
None
2 / 3
Rd
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#Clocks
AVRrc
Mnemonic Operands
Description
Op
Flags
LDD
LD
Rd, Y+q
Rd, Z
Load Indirect with Displacement
Load Indirect
Rd
Rd
←
←
(Y + q)
(Z)
None
None
None
N/A
1 / 2
2 / 3
LD
Rd, Z+
Load Indirect and Post-Increment
Rd
Z
←
←
(Z)
Z+1
LD
Rd, -Z
Load Indirect and Pre-Decrement
Z
←
←
Z - 1
(Z)
None
2 / 3
Rd
LDD
STS
ST
Rd, Z+q
k, Rr
Load Indirect with Displacement
Store Direct to Data Space
Store Indirect
Rd
(k)
(X)
←
←
←
(Z + q)
Rd
None
None
None
None
N/A
1
X, Rr
Rr
1
ST
X+, Rr
Store Indirect and Post-Increment
(X)
X
←
←
Rr
1
X + 1
ST
-X, Rr
Store Indirect and Pre-Decrement
X
←
←
X - 1
Rr
None
2
(X)
ST
ST
Y, Rr
Store Indirect
(Y)
←
Rr
None
None
1
1
Y+, Rr
Store Indirect and Post-Increment
(Y)
Y
←
←
Rr
Y + 1
ST
-Y, Rr
Store Indirect and Pre-Decrement
Y
←
←
Y - 1
Rr
None
2
(Y)
STD
ST
Y+q, Rr
Z, Rr
Store Indirect with Displacement
Store Indirect
(Y + q)
(Z)
←
←
Rr
Rr
None
None
None
N/A
1
ST
Z+, Rr
Store Indirect and Post-Increment
(Z)
Z
←
←
Rr
1
Z + 1
ST
-Z, Rr
Store Indirect and Pre-Decrement
Store Indirect with Displacement
Load Program Memory
In From I/O Location
Z
(Z + q)
R0
←
←
←
←
←
←
←
Z - 1
Rr
None
None
None
None
None
None
None
2
N/A
N/A
1
STD
LPM
IN
Z+q,Rr
(Z)
Rd, A
A, Rr
Rr
Rd
I/O(A)
Rr
OUT
PUSH
POP
Out To I/O Location
I/O(A)
STACK
Rd
1
(1)
1
Push Register on Stack
Pop Register from Stack
Rr
(1)
3
Rd
STACK
Table 24-4.ꢀBit and Bit-test Instructions
#Clocks
AVRrc
Mnemonic Operands
Description
Op
Flags
LSL
LSR
ROL
Rd
Rd
Rd
Logical Shift Left
Rd(n+1)
Rd(0)
C
←
←
←
Rd(n)
0
Z,C,N,V,H
1
1
1
Rd(7)
Logical Shift Right
Rd(n)
Rd(7)
C
←
←
←
Rd(n+1)
0
Z,C,N,V
Rd(0)
Rotate Left Through Carry
Rd(0)
Rd(n+1)
C
←
←
←
C
Z,C,N,V,H
Rd(n)
Rd(7)
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#Clocks
AVRrc
Mnemonic Operands
Description
Op
Flags
ROR
Rd
Rotate Right Through Carry
Rd(7)
Rd(n)
C
←
←
←
C
Z,C,N,V
1
Rd(n+1)
Rd(0)
ASR
SWAP
SBI
Rd
Arithmetic Shift Right
Swap Nibbles
Rd(n)
←
↔
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
←
Rd(n+1), n=0..6
Z,C,N,V
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Rd
Rd(3..0)
Rd(7..4)
None
A, b
A, b
Rr, b
Rd, b
s
Set Bit in I/O Register
Clear Bit in I/O Register
Bit Store from Register to T
Bit load from T to Register
Flag Set
I/O(A, b)
1
None
CBI
I/O(A, b)
0
None
BST
BLD
BSET
BCLR
SEC
CLC
SEN
CLN
SEZ
CLZ
SEI
T
Rr(b)
T
1
T
Rd(b)
None
SREG(s)
SREG(s)
s
Flag Clear
SREG(s)
0
SREG(s)
Set Carry
C
C
N
N
Z
Z
I
1
C
C
N
N
Z
Z
I
Clear Carry
0
Set Negative Flag
1
Clear Negative Flag
Set Zero Flag
0
1
Clear Zero Flag
0
Global Interrupt Enable
Global Interrupt Disable
Set Signed Test Flag
Clear Signed Test Flag
Set Two’s Complement Overflow
Clear Two’s Complement Overflow
Set T in SREG
1
CLI
I
0
I
SES
CLS
SEV
CLV
SET
CLT
S
S
V
V
T
T
H
H
1
S
S
V
V
T
T
H
H
0
1
0
1
Clear T in SREG
0
SEH
CLH
Set Half Carry Flag in SREG
Clear Half Carry Flag in SREG
1
0
Table 24-5.ꢀMCU Control Instructions
#Clocks
AVRrc
Mnemonic Operands
Description
Operation
Flags
BREAK
NOP
Break
(See also in Debug interface description)
None
None
None
None
1
1
1
1
No Operation
Sleep
SLEEP
WDR
(see also power management and sleep description)
(see also Watchdog Controller description)
Watchdog Reset
Note:ꢀ
1. Cycle time for data memory accesses assume internal RAM access, and are not valid for accesses
through the NVM controller. A minimum of one extra cycle must be added when accessing memory
through the NVM controller (such as Flash and EEPROM), but depending on simultaneous
accesses by other masters or the NVM controller state, there may be more than one extra cycle.
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26.
Packaging Information
26.1. 8-pin UDFN
Atmel ATtiny102 / ATtiny104 [DATASHEET]
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26.2. 8-pin SOIC150
Atmel ATtiny102 / ATtiny104 [DATASHEET]
251
Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
26.3. 14-pin SOIC150
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27.
Errata
27.1. ATtiny102
27.1.1. Rev.A
No known Errata.
27.2. ATtiny104
27.2.1. Rev.A
No known Errata.
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28.
Datasheet Revision History
28.1. Rev D - 10/2016
•
AVR CPU Core:
–
–
New section added, Accessing 16-bit Registers.
Stack Pointer (SPL and SPH) register updated.
•
USART - Universal Synchronous Asynchronous Receiver Transceiver:
–
–
Added UCSR0D.SFDE bit and corrected RXIE bit name to RXSIE.
Updated presentation of the UBRR0L and UBRR0H registers.
•
•
TC0 - 16-bit Timer/Counter0 with PWM:
–
Updated presentation of theTCNT0L and TCNT0H, OCR0AL and OCR0AH, and ICR0L and
ICR0H registers.
ADC - Analog to Digital Converter:
Updated the ADCL and ADCH registers (for both ADLAR=0 and 1).
–
28.2. Rev C - 07/2016
•
Thermal pad of 8-pin UDFN package should not be connected.
28.3. Rev B - 06/2016
•
•
Update Electrical Characteristics
Update Typical Characteristics
28.4. Rev A - 02/2016
Initial revision.
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2016 Atmel Corporation. / Rev.: Atmel-42505D-ATtiny102-ATtiny104_Datasheet_Complete-10/2016
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