TDC-GP21 [ETC]
Migration and Compatibility Guideline;
| 型号： | TDC-GP21 |
| 厂家： | 
ETC |
| 描述： | Migration and Compatibility Guideline |
| 文件： | 总6页 (文件大小：336K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
TDC-GP2 to TDC-GP21 Migration and
Compatibility Guideline
This paper is an add-on to the TDC-GP21 datasheet. It describes the functional and configuration
differences between TDC-GP2 and TDC-GP21.
Hardware and Software Compatibility
The TDC-GP21 offers an extended architecture that, within some very small restrictions, is fully
compatible to existing TDC- GP2 designs. According to its new features the GP21 configuration
register architecture is extended compared to TDC-GP2. However, the device supports 100%
downwards compatibility so there is no need for any hardware and software adaption when
switching your design from GP2 to GP21.
I/O supply voltage
The GP21 I/O supply voltage (Vio) is limited to max. 3.6 V, compared 5.5 V with TDC-GP2.
Chip marking
Basically, the GP21 chip marking is identical except for one difference. Compared to TDC-GP2 the
acam label on GP21 package might be rotated in some device charges. According to that we
strongly recommend to check the position of the orientation indicator (and not the acam label)
to ensure a correct PCB assembly of the device.
Fire out configuration
GP2 configurations where Fire1 and Fire2 are switched in parallel are not supported by the GP21.
This leads to a misbehaving of your system as the GP21 fire pulse generator will not generate any
output signals. In this case a small software modification is necessary that changes the settings of
CONF_FIRE parameter in configuration register 5.
To get access to the device’s extended functionality some hardware- and software modifications are
necessary.
32 kHz Oscillator
Basically, the TDC-GP21 offers full clock signal compatibility to TDC-GP2. With GP21 the internal 32
kHz clock driver has an additional low power option. This reduces current consumption of the 32 kHz
quartz to typ. 600 nA (compared to typ. 4.5 µA in GP2). So the stand by current of the GP21 with
active 32 kHz clock is reduced to 1 µA.
Table 1: Current consumption of 32 kHz clock source in GP2 /GP21
TDC-GP2
Min. Typ.
4.5
TDC-GP21
Min. Typ.
0.6
Symbol
I32
Description
Current 32 kHz
Max.
Max. Unit
µA
Also the TDC-GP21 offers enhanced clock options for clock distribution via FIRE_IN pin. They are
available via register 1 configuration. According to that, FIRE_IN can be defined as a 32.768 Hz or
4.096 Hz clock signal output, e. g. as a low-current clock signal source for an external microprocessor.
Table 2 provides the details:
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Table 2: Parameters for enhanced clock options of TDC-GP21
Parameter
SEL_TSTO2
Terminal
Reg1[11:13]
Description
Value
Additional functionality
of Fire_In pin for clock
signal output
Low power option for 32 1 = enabled (recommended)
kHz clock 0 = disabled
7 = 4 kHz out (32 kHz / 8)
SEL_TSTO1
Curr32
Reg1[10:8]
Reg1[15]
7 = 32 kHz out
Time measurement unit
The base resolution of the GP21 is typ. 90 ps. In measure mode 2 it can be improved by setting
Double resolution (typ. 45 ps) and Quad resolution (typ. 22 ps) mode. For GP2 compatibility the GP21
by default operates in standard mode (GP2 mode, 90 ps resolution). Configuring higher resolution
requires write access to configuration register 6. This register is part of the extended register
architecture of the TDC-GP21. Setting bit 12 or 13 activates double or quad resolution mode
Table 3: GP21 Double and Quad resolution mode
Parameter
QUAD_RES
Terminal
Reg6[13]
Description
Improves resolution from 90
ps to 22 ps in measure mode 2 1 = 0n
Value
0 = off (GP2 compatibility)
Improves resolution from 90
ps to 45 ps in measure mode 1
and 2
0 = off (GP2 compatibility)
1 = 0n
DOUBLE_RES
Reg6[12]
All details about the TDC-GP21 register architecture are available in chapter 3 of the datasheet.
Fire Pulse generator
With GP21 the maximum number of send pulses has been increased to 127. A detailed description of
the fire pulse generator is available in TDC-GP21 datasheet section 5.2.1. Information about the
correct configuration is described in section 5.2.2.
Table 4: New parameters for GP21 fire pulse generator
Parameter
Terminal
Description
Value
Reg0[31:28]
Reg6[10:8]
0 = off
127 = 127 pules
ANZ_FIRE
Sets number of pulses
Bit 23 = 1: Fire both
Bit 22 = 1: disable Fire_Up
Bit 21 = 1: disable Fire_Down
0 = GP2 behaviour
1 = use Fire as TDC start
0 = High-Z (GP2-Mode)
1 = Low (mandatory to use
analog input section)
Output configuration for pulse
generator
CONF_FIRE
Reg5[31:29]
Reg1[14]
SEL_START_FIRE
FIRE_DEFAULT
Uses fire pulse signal as start
Specifies default level of
inactive fire buffer
Reg6[14]
Analog input section
The TDC-GP21 integrates a complete analog section. It can be used alternatively to the pure digital
input. This significantly simplifies the design of ultrasonic flow and heat meters, which is one of the
main application areas of the TDC-GP21.
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The signals are coupled to the TDC-GP2 analog inputs by means of a high pass filter. This is necessary
as the comparator cannot handle GND as threshold. Thus, the input signal level of the non-inverted
comparator input is switched to 1/3 Vcc. According to that the comparators threshold is also 1/3 Vcc.
Figure 1 shows the corresponding oscilloscope trace.
Figure 1: Signal curve on non-inverted comparator input. (measured at TP1)
Received pulse
sequence
LoadC charging to 1/3Vcc
(comparator threshold)
Send pulses
The GP21 integrates complete control for a measurement cycle. Figure 2 shows an oscilloscope trace
of a measurement cycle with a 1 MHz signal burst (20 pulses).
Figure 2: Oscillogram of a complete measurement cycle (measured at TP2 and TP3)
Send pulses
Received pulse
sequence
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According to the received pulse sequence the integrated comparator generates a digital output
signal that is internally feed into stop1 input. With SEL_TST1 = 6 (configuration register 6) the
comparator output signal is available on FIRE_IN pin,(e. g. for hardware diagnosis) as shown below.
Figure 3: Received pulse sequence and corresponding comparator output signal
Comparator
output signal
Received pulse
packet
Table 6: Configuration parameters that are relevant for the GP21 analog section
Parameter Terminal
EN_Analog Reg6[31]
Description
Value
0 = Stop1 and Stop2 are digital
inputs (GP2 compatibility)
1 = activates analog section
Activates analog part for ultrasonic
flow measurements
0 = 90 µs
1 = 120 µs
2 = 150 µs
3 = 300 µs
0 = 1
1 = 1.5
2 = 2
3 = 2.5
Sets charge time of capacitor LoadC
when the integrated analog section
is used
TW2
Reg6[23:22]
Selects timer for triggering the
second Time-of-Flight measurement
in multiples of 50/60 Hz
CYCLE_TOF Reg6[17:16]
Forces GP21 to execute a complete
up and down flow measurement
cycle and two temperature
measurement in series. The time
interval between two measurements
is based on 50 / 60 Hz
0 = 50 Hz base (20 ms)
1 = 60 Hz base (16.67 ms)
HZ60
Reg6[15]
A detailed description of the analog section is available in section 4.3 of the TDC-GP21 datasheet.
Temperature measuring unit
The GP21 temperature measurement unit has the comparator already integrated. Due to GP2
compatibility it also works with an external Schmitt Trigger. Here we recommend the 74AHC14 to get
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best results. The functional details are described in section 4.4 of the datasheet. The following table
provides an overview of the relevant configuration parameters.
Additionally, the GP21 provides the opportunity to execute two cyclic temperature measurements
that are synchronized with 50/60 Hz, in order to reduce 50/60 Hz noise. Here, the TDC-GP21
automatically starts the second temperature measurement after the selected time (Cycle_TEMP).
When using this option, it important that the first measurement result has to be read out before the
second temperature measurement is started by the GP21. Otherwise it will be overwritten after the
second temperature measurement has been finished.
Table 8: Additional configuration Parameters for GP21 temperature measurement unit
Parameter
Terminal
Description
Value
Inverts the SenseT input
signal. Has to be set when
internal Schmitt-trigger is uses
trigger
0 = external Schmitt Trigger
(GP2 compatibility)
1 = internal Schmitt-trigger
NEG_STOP_TEMP Reg6[30]
Selects timer for triggering the 0 = 1
second temperature
measurement in multiples of
50/60 Hz
1 = 1.5
2 = 2
3 = 2.5
Cycle_TEMP
Reg6[19:18]
Option for measuring the
temperature ports in the
opposite order
0 = PT1>PT2>PT3>PT4
1 = PT4>PT3>PT2>PT1
TEMP_PORT_DIR Reg6[11]
Sets base frequency for delay
between up and down
measurement
0 = 50 Hz base
1 = 60 Hz base
HZ60
Reg6[15]
Configuration Register Architecture
The GP21 includes 7 configuration registers, each with 32-bit width (compared to 6 x 24 bit in GP2).
The register organization is fully downwards compatible to GP2. To get access to the extended
configuration space in order to use the enhanced GP2 functionality, the SPI communication has to be
expanded by one additional byte of configuration data.
TDC-GP2:
TDC-GP21:
Opcode + Address + 3 Bytes configuration data
Opcode + Address + 4 Bytes configuration data
The complete register set is described in section 3 of the datasheet. Details about the SPI
communication can be found in section 3.4.
Internal EEPROM
The TDC-GP21 integrates a 7x32 bit EEPROM that can be used to store the configuration data
together with a system ID or version number. For details please refer to section 3.3 of the datasheet.
Interrupt sources
The GP21 interrupt behavior is expanded by an additional interrupt source, that especially refers to
EEPROM access. It has to be enabled by activating bit 21 in configuration registers 6. Then the end of
an EEPROM action is indicated by an Interrupt.
Table 9: EEPRPOM action as interrupt source
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Parameter
EN_INT[3]
Terminal
Reg6[21]
Description
Value
Highest bit to enable additional
EEPROM action as additional
interrupt source. See also register 2
for lower 3 bits (GP2 compatible
interrupt sources)
0 = disable EEPROM action
as interrupt (GP2
compatibility)
1 = end of EEPROM action
is indicates by an interrupt
Basic Reference Design
Test measurements were made with a GP21 hardware connected to a Weihai Ploumeter spoolspiece
with 1 MHz transducers. TP1 to TP3 indicate the test points where the oscilloscope has been
connected.
Circuit Schematic, Testpoints and Register Configuration
Figure 4: circuit schematic
TP2
TP1
TP3
The following register configuration has been used for the test measurement.
Table 10: Content of TDC-GP21 configuration registers
Configuration Register Address
Register Content
0xA30B6800
0x21044000
0x2024B800
0x102A3000
0x202AF855
0x40000000
0cC0006000
Register 0
Register 1
Register 2
Register 3
Register 4
Register 5
Register 6
0
1
2
3
4
5
6
Related Documentation
acam-messelectronic gmbh -, “TDC-GP21 datasheet”, available from www.acam.de
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