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Ultrasonic-Flow-Converter
Data Sheet
TDC-GP21
Universal 2-Channel
Time-to-Digital Converters
March 13 th 2014
Document-No: DB_GP21_en V1.6
Member of the ams Group
UFC
TDC-GP21
Published by acam -messelectronic gmbh
©acam-messelectronic gmbh 2014
Disclaimer / Notes
“Preliminary” product information describes a product which is not in full production so
that full information about the product is not available yet. Therefore, acam-messelectronic
gmbh (“acam”) reserves the right to modify this product without notice. The information
provided by this data sheet is believed to be accurate and reliable. However, no
responsibility is assumed by acam for its use, nor for any infringements of patents or
other rights of third parties that may result from its use. The information is subject to
change without notice and is provided “as is” without warranty of any kind (expressed or
implied). All other brand and product names in this document are trademarks or service
marks of their respective owners.
Support / Contact
For a complete listing of Direct Sales, Distributor and Sales Representative contacts, visit
the acam web site at:
http://www.acam.de/sales/distributors/
For technical support you can contact the acam support team in the headquarters in
Germany or the Distributor in your country. The contact details of acam in Germany are:
[email protected]
or by phone
Member of the ams Group
+49-7244-74190.
TDC-GP21
Content
1
2
3
4
5
6
Overview .................................................................................................. 1-3
1.1
Features ............................................................................................. 1-3
1.2
Blockdiagram ...................................................................................... 1-5
1.3
Ordering Numbers ................................................................................ 1-5
Characteristics & Specifications ................................................................... 2-1
2.1
Electrical Characteristics ....................................................................... 2-1
2.2
Converter Specification .......................................................................... 2-4
2.3
Timings .............................................................................................. 2-7
2.4
Pin Description .................................................................................. 2-10
2.5
Package Drawings .............................................................................. 2-12
2.6
Power Supply ..................................................................................... 2-14
Registers & Communication ......................................................................... 3-1
3.1
Configuration registers .......................................................................... 3-1
3.2
Read registers ................................................................................... 3-12
3.3
EEPROM ........................................................................................... 3-15
3.4
SPI-interface ..................................................................................... 3-16
Converter Frontend .................................................................................... 4-1
4.1
TDC - Measurement mode 1 .................................................................. 4-1
4.2
TDC - Measurement mode 2 .................................................................. 4-9
4.3
Analog Input Section ........................................................................... 4-17
4.4
Temperature Measurement .................................................................. 4-20
Details and Special Functions ....................................................................... 5-1
5.1
Oscillator ............................................................................................ 5-1
5.2
Fire Pulse Generator ............................................................................. 5-4
5.3
Fast Initialization .................................................................................. 5-7
5.4
Noise Unit .......................................................................................... 5-8
5.5
EMC Measures .................................................................................... 5-9
Applications .............................................................................................. 6-1
6.1
7
Ultrasonic Heat Meter .......................................................................... 6-1
Miscellaneous ........................................................................................... 7-1
7.1
Bug Report ......................................................................................... 7-1
7.2
Last Changes ...................................................................................... 7-2
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1-2
TDC-GP21
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TDC-GP21
1
Overview
TDC-GP21 is next generation‘s upgrade for TDC-GP2. It offers pin-to-pin and functional
compatibility, several feature improvements and an extended functionality. Analog elements like a
chopper stabilized comparator and analog switches simplify external circuits in a significant
manner. In parallel, measurement quality is improved and operating current is reduced. The
firepulse generator is extended, a new low-power 32 kHz oscillator driver is implemented and the
temperature measuring unit is further improved. All in all, the TDC-GP21 is perfectly suited to
design ultra-compact and low-cost ultrasonic flow meters and heat meters. If the integrated
analog elements of the TDC-GP21 are used, the average operating current of a typical heatmeter
application can be reduced to 2.2 µA.
1.1
Features
Measurement mode 2

1 channel with typ. 90 ps resolution

Double resolution mode with 45 ps, Quad resolution mode with 22 ps resolution

Measurement range 700 ns to 4 ms

3-fold multihit capability with automatic processing of all 3 data
Analog Input Circuit

Chopper-stabilized low-offset comparator

Offset programmable, -8 to 7 mV

Integrated analog switches for input selection

External circuit is reduced to 2 resistors and 2 capacitors
Temperature Measurement Unit

2 or 4 sensors, PT500/PT1000 or higher

Schmitt trigger integrated

16-Bit eff. with external Schmitt trigger, 17.5-Bit eff. with integrated low noise
Schmitt trigger

Ultra low current (0.08 µA when measuring every 30 seconds)
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Ultrasonic-Flow-Converter
TDC-GP21
Special Functions

Fire pulse generator, up to 127 pulses

Trigger to rising and/or falling edge

Precise stop enable by windowing

Low-power 32 kHz oscillator (500 nA)

Clock calibration unit

7x32 Bit EEPROM
Measurement mode 1

2 channels with typ. 90 ps resolution

channel double resolution with typ. 45 ps

Range 3.5 ns (0 ns) to 2.5 µs

20 ns pulse-pair resolution, 4-fold multihit

Up to 500 000 measurements per second in measurement mode 1
General
1-4

4-wire SPI interface

500 kHz continuous data rate max.

I/O voltage 2.5 V to 3.6 V

Core voltage 2.5 V to 3.6 V

Temperature range – 40 °C to +85 °C

QFN 32 Package
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TDC-GP21
1.2
Blockdiagram
1.3
Ordering Numbers
Part#
Package
Package Qty; Carrier
Order number
TDC-GP21
QFN32
5000/3000; T&R
MNR 1720
TDC-GP21
QFN32
490; Tray
MNR 1839
GP21-EVA-KIT
System
1; Box
MNR 1781
This product is RoHS compliant and does not contain any Pb.
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Ultrasonic-Flow-Converter
1-6
TDC-GP21
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TDC-GP21
2
Characteristics & Specifications
2.1
Electrical Characteristics
Absolute Maximum Ratings
Supply voltage
V cc vs. GND
- 0.3 to 4.0
V
V io vs. GND
- 0.3 to 4.0
V
- 0.5 to V cc + 0.5
V
V in
Storage temperature (T stg )
- 55 to 150
°C
> 2
kV
max.125
°C
ESD rating (HBM), each pin
Junction temperature (T j )
Recommended Operating Conditions
Symbol
Parameter
Conditions
Min
V cc
Core supply voltage 1
V io = V cc
V io
I/O supply voltage
t ri
Max
Unit
2.5
3.6
V
2.5
3.6
V
Normal input rising time
200
ns
t fa
Normal input falling time
200
ns
t ri
Schmitt trigger rising time
5
ms
t fa
Schmitt trigger falling time
5
ms
Ta
Ambient temperature
T j must not exceed -40
125°C
125
°C
R th(j-a)
Thermal resistance
junction-ambient
1
Typ
28
K/W
including the oscillator pins XIN, XOUT, Clk32In, Clk32Out
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Ultrasonic-Flow-Converter
TDC-GP21
DC Characteristics (V io = V cc = 3.0 V, T j = -40 to +85°C)
Symbol
Parameter
Conditions
I 32
Current 32 kHz
I cc + I io , only 32 kHz
oscillator running
1.0
µA
I hs
Current 4 MHz oscillator
V cc = V io = 3.6 V
= 3.0 V
off
200
130
< 1
µA
µA
nA
I tmu
Current time measuring
unit
only during active
time measurement
4
mA
I ddq
Quiescent current
all clocks off, @ 85
°C
< 0.1
µA
Io
Operating current
TOF_UP/DOWN, 1/s
Temperature
average, PT1000,
1/30s
1.1
0.15
µA
V oh
High level output voltage
I oh = tbd mA V io =Min.
V ol
Low level output voltage
I ol = tbd mA, V io =Min
V ih
High level input voltage
LVTTL Level, V io =
Max.
V il
Low level input voltage
LVTTL Level, V io =
Min.
V th
High level Schmitt trigger
voltage
V tl
Low level Schmitt trigger
voltage
Vh
Schmitt trigger
hysteresis
2-2
Min
Typ
Max
0.8V io
V
0.2V io
0.7V io
V
V
0.3V io
0.7Vio
V
V
0.3V io
0.28
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Unit
V
V
TDC-GP21
Terminal Capacitance
Symbol
Terminal
Condition
Rated Value
Min.
measured @ V cc = V io ,
f = 1 MHz,
T a = 25°C
Typ.
Ci
Digital input
Co
Digital output
C io
Bidirectional
9
PT ports
t.b.d.
Analog in
t.b.d.
Unit
Max.
7
pF
Analog Frontend
Symbol
Terminal
Condition
Rated Value
Min.
Unit
Typ.
Max.
Comparator input offset
voltage (chopper stabilized)
< 1
2
R dson(AS)
Switch-on resistance of
analog switches at
STOP1/STOP2 inputs
200
Ohm
R dson(FIRE)
Switch-on resistance of
FIRE_UP, FIRE_DOWN
output buffers
4
Ohm
I fire
Output current FIRE_UP,
FIRE_DOWN output buffers
48
mA
Symmetrical
outputs,
Rdson(HIGH) =
Rdson(LOW)
mV
EEPROM
Symbol
Terminal
Condition
Minimum Value
Unit
Data retention @ 85°C
normal
10
years
with Error
correction
practically endless
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2.2
TDC-GP21
Converter Specification
Time Measuring Unit (V io = V cc = 3.0 V, T j = 25°C)
Symbol
Terminal
Condition
Rated Value
Min.
LSB
Resolution (BIN-Size)
Measurement mode 1
& 2:
DOUBLE_RES = 0
DOUBLE_RES = 1
Standard deviation
Measurement Mode 2
tm
Measurement range
Max.
ps
90
45
Measurement mode 2:
QUAD_RES = 1
Standard deviation
Measurement Mode 1
Typ.
Unit
ps
22
DOUBLE_RES = 0
Delay = 200ns
Delay = 1µs
DOUBLE_RES = 1
Delay = 200ns
ps
45
72
35
DOUBLE_RES = 0
Delay = 2µs
Delay = 100µs
DOUBLE_RES = 1
Delay = 2µs
Delay = 100µs
QUAD_RES = 1
Delay = 2µs
Delay = 100µs
ps
54
70
50
62
39
62
Measurement mode 1
3.5 ns
2.4 µs
=26224
*LSB
Measurement mode 2
700 ns
4 ms
INL
Integral Non-linearity
< 0.1
LSB
DNL
Differential Nonlinearity
< 0.8
LSB
2-4
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TDC-GP21
Figure 2-1 Relative Variation of un-calibrated least significant bit with temperature and supply
voltage, reference 3.0V/25°C
1.40
3.6 V
1.30
LSB / (LSB @ 25°C, 3.0 V)
3.0 V
1.20
2.5 V
1.10
1.00
0.90
0.80
-5
-25
15
35
55
75
95
Temperature [°C]
Temperature Measuring Unit
Symbol
1
Terminal
2
Internal Schmitt trigger
external Schmitt trigger
PT500
PT1000
PT500
PT1000
Resolution RMS
17.5
17.5
16.0
16.0
Bit
SNR
105
105
96
96
dB
Absolute Gain 3
0.9912
0.9931
0.9960
0.9979
3.6 V
0.9923
0.9940
0.9962
0.9980
3.0 V
0.9912
0.9931
0.9960
0.9979
2.5 V
0.9895
0.9915
0.9956
0.9979
0,25
0.23
0.06
0.04
Absolute Gain vs.
V io 3
Gain-Drift vs. V io
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Unit
%/V
2-5
Ultrasonic-Flow-Converter
TDC-GP21
max. Gain Error
(@ dӨ = 100 K)
0,05%
0,05%
0,02%
< 0.01%
Gain-Drift vs. Temp
0.022
0.017
0.012
0.0082
Gain-Drift vs. Vio
0,08
%/V
Initial Zero Offset
< 20
<10
< 20
< 10
mK
Offset Drift vs. Temp
< 0.05
< 0.03
< 0,012
< 0.0082
mK/ °C
PSRR
1
%/10
K
>100
dB
All values measured at Vio = Vcc = 3.0 V, Cload = 100 nF for PT1000 and 200 nF for
PT500 (C0G-type)
2
measured with external 74AHC14 Schmitt trigger
3
compared to an ideal gain of 1
2-6
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2.3
Timings
At Vcc = 3.0 V ± 0.3 V, ambient temperature -40 °C to +85 °C unless otherwise specified
Oscillator
Symbol
Parameter
Min.
Clk32
32 kHz reference oscillator
32,768
kHz
t 32st
32 kHz oscillator start-up time after power-up
250
ms
ClkHS
High-speed reference oscillator
t oszst
Oscillator start-up time with ceramic resonator
100
µs
t oszst
Oscillator start-up time with crystal oscillator
3
ms
2
Typ.
Max.
4
8
Unit
MHz
Note:
It is strongly recommended to use a ceramic oscillator. Exactly because a quartz needs
much longer to settle than a ceramic oscillator. This costs a lot current, but using a
quartz oscillator has no advantage.
Serial Interface
Symbol
Parameter
Max. @ V io =
Unit
2.5 V
3.3 V
20
f clk
Serial clock frequency
15
Symbol
Parameter
Min. @ V io =
MHz
Unit
2.5 V
3.3 V
t pwh
Serial clock, pulse width high
30
25
ns
t pwl
Serial clock, pulse width low
30
25
ns
t sussn
SSN enable to valid latch clock
40
10
ns
t pwssn
SSN pulse width between write cycles
50
40
ns
t hssn
SSN hold time after SCLK falling
40
25
ns
t sud
Data set-up time prior to SCLK falling
5
5
ns
t hd
Data hold time before SCLK falling
5
5
ns
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Symbol
TDC-GP21
Parameter
t vd
Max. @ V io =
Data valid after SCLK rising
Unit
2.5 V
3.3 V
20
16
Serial Interface (SPI compatible, Clock Phase Bit =1, Clock Polarity Bit =0):
tsussn
tpwssn
tpwl
tpwh
SSN
thssn
SCK
SI
MSB
LSB
tsud
thd
Figure 2-2 SPI Write
tsussn
tpwl
tpwssn
tpwh
SSN
SCK
SI
MSB
1
6
tsud
LSB
thd
SO
MSB
1
MSB-1
LSB
tvd
OPCODE
DATA
Figure 2-3 SPI Read
Disable Timings
STOP
no pass
pass
EN_Stop
STOP
no pass
pass
EN_Stop
tS-EN
tSH-EN
Figure 2-4 Disable Timings
Spec
Description
Measurement mode 1
Measurement mode 2
t S-EN
Enable Setup Time
0 ns
0 ns
t SH-EN
Enable Hold Time
1.5 ns
3.0 ns
2-8
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ns
TDC-GP21
Reset Timings
Figure 2-5 Reset Timings
Spec
Description
Typ. Min
t ph
Reset pulse width
50 ns
t rfs
Time after rising edge of reset
pulse before further
communication
200 ns
Time after rising edge of reset
pulse before analog section is
ready
500 µs
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2.4
TDC-GP21
Pin Description
Figure 2-6 TDC-GP21 Pinout
No.
Name
Description
1
XIN
Oscillator driver in
2
XOUT
Oscillator driver out
3
VIO
I/O – supply voltage
4
GND
Ground
5
FIRE_UP
Fire pulse generator output 1
48 mA
6
FIRE_DOWN Fire pulse generator output 2
48 mA
7
FIRE_IN
Diagnostics output
8
INTN
Interrupt flag
9
SSN
Slave select
10
SCK
Clock serial interface
2-10
Buffer type
Value
If not
used
GND
GND
4 mA
LOW active
LOW active
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No.
Name
Description
Buffer type
Value
If not
used
11
SI
Data input serial interface
12
SO
Data output serial interface
13
RSTN
Reset input
14
VCC
Core supply voltage
15
CLK32OUT
Output 32 kHz clock generator
n. c.
16
CLK32IN
Input 32 kHz clock generator
GND
17
SENSET
Sense input temperature
measurement
Schmitt
trigger
GND
18
LOADT
Load output temperature
measurement
24 mA
n.c.
19
PT4*
Port 4 temperature
measurement
> 96 mA open
drain
20
PT3*
Port 3 temperature
measurement
> 96 mA open
drain
21
GND
Ground
22
VIO
I/O – supply voltage
23
PT2*
Port 2 temperature
measurement
> 96 mA open
drain
24
PT1*
Port 1 temperature
measurement
> 96 mA open
drain
25
EN_STOP2
Enable pin stop input 2
HIGH
active
VIO
26
EN_STOP1
Enable pin stop input 1
HIGH
active
VIO
27
STOP2
Stop input 2
28
GND
Ground
29
VCC
Core supply voltage
30
STOP1
Stop input 1
31
START
Start input
32
EN_START
Enable pin start input
4 mA tristate
LOW active
GND
GND
HIGH
active
VIO
* R DSON temperature ports: typ. 1.8 Ω @ 3.0 V
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2.5
TDC-GP21
Package Drawings
Figure 2-7 QFN-32 package outline, 5 x 5 x 0.9 mm³, 0.5 mm lead pitch
Caution: Center pad, 3.70 * 3.70 mm², is internally connected to GND. No wires other
than GND are allowed underneath. It is not necessary to connect the center pad to GND.
Suitable socket: Plastronics 32QN50S15050D
Landing Pattern:
Figure 2-8
2-12
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Thermal resistance: Roughly 28 K/W (value just for reference).
Environmental: The package is RoHS compliant and does not contain any Pb.
Moisture Sensitive Level (MSL)
Based on JEDEC 020 Moisture Sensitivity Level definition the TDC -GP21 is classified as
MSL 1.
Soldering Temperature Profile
The temperature profile for infrared reflow furnace (in which the temperature is the resin’s
surface temperature) should be maintained within the range described below.
Figure 2-9 Soldering profile
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TDC-GP21
Maximum temperature
The maximum temperature requirement for the resin surface, given 260ºC as the peak
temperature of the package body’s surface, is that the resin surface temperature must
not exceed 250ºC for more than 10 seconds. This temperature should be kept as low as
possible to reduce the load caused by thermal stress on the package , which is why
soldering for short periods only is recommended. In addition to using a suitable
temperature profile, we also recommend that you check carefully to confirm good
soldering results.
Date Code: YYWWA: YY = Year, WW = week, A = Assembly site code
2.6
Power Supply
Supply voltage
TDC-GP21 is a high end mixed analog/digital device. To reach full performance of the chip
a good power supply is mandatory. It should be high capacitive and of low inductance.
The TDC-GP21 provides two pairs of power supply terminals:
Vio
- I/O supply voltage
Vcc
- Core supply voltage
Figure 2-10
Both voltages should be applied with low series resistance from the same source. On the
chip there are connected, but a separate external connection is recommended for good
measurement quality. All ground pins should be connected to a ground plane on the
2-14
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TDC-GP21
printed circuit board. Vio and Vcc should be provided by a battery or fixed linear vol tage
regulator. Do not use switched regulators to avoid disturbances caused by the I/O supply.
Vio and Vcc are connected internally on the chip. The resistance between both is in the
range of several Ohms. However, Vio is connected to the pads with significantly lower
impedance and therefore can provide this better than Vcc.
The measurement quality of a time-to-digital converter depends on a good power supply.
The chip sees mainly pulsed current and therefore a sufficient bypassing is mandatory:
Vcc
47 to 100 µF
(minimum 22 µF)
Vio
100 µF
(minimum 22 µF)
The supply voltage should be provided through analog regulators. We strongly recommend
not to use switch mode power supplies.
Current consumption
The current consumption is the sum from different parties (all data for Vio = Vcc = 3.0V):
I ddq
< 5 nA [email protected],
Quiescent current, no 32 kHz oscillator running
25°C
I 32
typ. 1.0 µA
Standby current with active 32 kHz oscillator ( GP21 waiting for
command).
I hs
typ. 130 µA/s
Current into the high speed oscillator at 3.0 V Vio.
* (active runtime)
Example: In ultrasonic flow-meters the high-speed oscillator is on for
about 2ms only.
The average current consumption is 130 µA/s * 2 ms = 0.26 µA
I tmu
typ. 4 mA/s
Current into the time measuring unit, In measurement mode 1
* (active measuring
The time measuring unit is active for the start-stop time interval plus
time)
the calibration time interval of 2 periods of the reference clock per
measurement.
In measurement mode 2 the time measuring unit is on for average 4
periods of the reference clock per measuremen t, two for the time
measurement and two for calibration.
Example: With 10 measurements per second in measurement mode
2 and a 4 MHz reference clock the time measuring unit is active for
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TDC-GP21
only about 10 µs.
The average current is 4 mA/s * 10 µs = 0.040 µA.
I ALU
typ. 7 nA per
Current into ALU during data proccesing including a calibration
calculation
calculation.
Example: At 1000 measurements per second with 3 stops per start
the ALU average current is 7 nA * 3000 = 21 µA.
IT
typ. 2.5 µAs
The current for a full temperature measurement is typ.2.5µAs.
* measure rate
In heat-meters the temperature is measured typically once every 30
seconds. The average current is about 0.085 µA
I ana
typ. 0.8 mA
Current consumption of the integrated analog part of TDC-GP21
during a Time-of-flight (ToF) measurement. The analog part is active
for a duration of 250 µs + ToF.
2-16
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TDC-GP21
3
Registers & Communication
3.1
Configuration registers
The TDC-GP21 has 7 configuration registers with 32 bit. The upper 24 bit are used for
configuration and are write only. They are used to setup the TDC-GP21 operating mode.
The lowest 8 bit can be used e.g. as an ID and can be read back.
For communication test please write to register 1 and read back the highest 8 bit from
address 5.
Note:
The write registers of TDC-GP21 are fully upwards compatible with TDC-GP2. A given
configuration of TDC-GP2 can directly be used one-to-one in TDC-GP21. The TDC-GP21
than works as a TDC-GP2. The add-on functionality can be selected in register 6 and reg1
Bits 7:0 which are not used in GP2. For proper work of TDC-GP21, a power-up reset via
pin or SPI command is necessary after the power-up of the circuit.
3.1.1
Alphanumeric listing of configuration parameters
Table 3-1: Configuration Parameters
Parameter
Old name (TDC-GP2)
Register
Bits
Default
value
ANZ_FAKE
No_Fake
0
15
0
Fire#
0
6
28-31
8-10
2
ANZ_PER_CALRES
CALRES#
0
22,23
0
ANZ_PORT
PORT#
0
17
1
CALIBRATE
Calibrate
0
13
1
CON_FIRE
CONF_FIRE
5
28-31
0
CURR32K
1
15
0
x
CYCLE_TEMP
6
18,19
0
x
CYCLE_TOF
6
16,17
0
x
ANZ_FIRE
[3:0]
[6:4]
DELVAL1
DELVAL1
2
8-23
0
DELVAL2
DELVAL2
3
8-23
0
DELVAL3
DELVAL3
4
8-23
0
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New or
modified
x
3-1
Ultrasonic-Flow-Converter
TDC-GP21
Parameter
Old name (TDC-GP2)
Register
Bits
Default
value
DIS_PHASESHIFT
Dis_PhaseNoise
5
27
0
DIV_CLKHS
ClkHSDiv
0
20,21
0
DIV_FIRE
DIV_FIRE
0
24-27
2
DOUBLE_RES
6
12
0
x
EN_ANALOG
6
31
0
x
EN_ERR_VAL
EN_ERR_VAL
3
29
0
EN_FAST_INIT
EN_FAST_INIT
1
23
0
EN_INT
2
6
29-31
21
1
EN_STARTNOISE
5
28
0
6
14
0
EN_INT
[2:0]
[3]
EN_STARTNOISE
FIREO_DEF
New or
modified
x
x
HIT1
HIT1
1
24-27
5
HIT2
HIT2
1
28-31
5
HITIN1
HITIN1
1
16-18
0
HITIN2
HITIN2
1
19-21
0
HZ60
6
15
0
x
ID0
0
0-7
0
x
ID1
1
0-7
0
x
ID2
2
0-7
0
x
ID3
3
0-7
0
x
ID4
4
0-7
0
x
ID5
5
0-7
0
x
ID6
6
0-7
0
x
MESSB2
MRange2
0
11
1
NEG_START
NEG_START
0
8
0
6
30
0
NEG_STOP_TEMP
NEG_STOP1
NEG_STOP1
0
9
0
NEG_STOP2
NEG_STOP2
0
10
0
NO_CAL_AUTO
DisAutoCal
0
12
0
PHFIRE
Phase_Fire
5
8-23
0
6
13
0
QUAD_RES
3-2
x
x
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TDC-GP21
Parameter
Old name (TDC-GP2)
Register
Bits
Default
value
REPEAT_FIRE
REPEAT_FIRE
5
24-26
0
RFEDGE1
RFEDGE1
2
27
0
RFEDGE2
RFEDGE2
2
28
0
SEL_ECLK_TMP
SelClkT
0
14
1
1
14
0
3
27,28
3
SEL_TSTO1
1
8-10
0
x
SEL_TSTO2
1
11-13
0
x
START_ClkHS
0
6
18,19
20
1
x
TCycle
0
16
0
TEMP_PORTDIR
6
11
0
x
TW2
6
22,23
0
x
SEL_START_FIRE
SEL_TIMO_MB2
START_CLKHS
TCYCLE
SEL_TIMO_MR2
[1:0]
[2]
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New or
modified
x
3-3
Ultrasonic-Flow-Converter
3.1.2
TDC-GP21
List of configuration registers
15
Bit number 
14
13
Parameter 
12
11
10
9
8
7
param1
6
5
4
3
2
1
0
1
0
1
0
k.d.
Default value 
1
1
0
0
1
0
19
18
17
16
15
14
k.d. = keep default values
Register 0 (address 0):
31
30
29
28
27
ANZ_FIRE[3:0]
0
0
1
0
26
25
24
23
22
21
20
13
12
11
10
8
DIV_FIRE
0
0
1
7-0
ID0
0
0
0
0
0
0
1
1
0
0
1
1
0
1
0
Parameter
Description
Settings
ANZ_FIRE[3:0]
(FIRE#)
Sets number of pulses generated by fire
pulse generator. Additional 3 bits are set in
register 6.
For values ANZ_FIRE > 15 the phase setting
(PHFIRE) can not be used.
0 = off
1 = 1 pulse
2 = 2 pulses
…
127 = 127 pulses
DIV_FIRE
Sets predivider for internal clock signal of fire
pulse generator
0 = not permitted
1 = divided by 2
2 = divided by 3
3.= divided by 4
…
15 = divided by 16
ANZ_PER_CALRES
(CALRES#)
Sets number of periods used for calibrating
the ceramic resonator
0
1
2
3
=
=
=
=
2 periods = 61.035 µs
4 periods = 122.07 µs
8 periods = 244.14 µs
16 periods = 488.281 µs
DIV_CLKHS
(ClkHSDiv)
Sets predivider for CLKHS
0
1
2
3
=
=
=
=
divided
divided
divided
divided
3-4
9
by
by
by
by
1
2
4
4 (also)
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0
0
0
TDC-GP21
START_CLKHS[1:0] Defines the time interval the chip waits after
switching on the oscillator before making a
measurement.
Note:
The highest bit to adjust START_CLKS is
located in register 6, bit 20. This has to be
set to 1 for settling times of 2.44 ms and
5.14 ms.
0
1
2
3
4
5
= Oscillator off
= Oscillator continuously on
= settling time 480 µs
= settling time 1.46 ms
= settling time 2.44 ms
to 7 = settling time 5.14 ms
ANZ_PORT
(PORT#)
Sets number of ports used for temperature
measurement
0 = 2 temperature ports (PT1 and PT2)
1 = 4 temperature ports
TCYCLE
Sets cycle time for temperature
measurement
0 = 128 µs cycle time @ 4 MHz
1 = 512 µs cycle time @ 4 MHz
(recommended)
ANZ_FAKE
(FAKE#)
Number of dummy cycles at the beginning of
a temperature measurement
0 = 2 Fake measurements
1 = 7 Fake measurements
SEL_ECLK_TMP
(SelClkT)
Select reference signal for internal cycle
clock for temperature measurement
0 = use 32.768 kHz as cycle clock
1 = use 128 * CLKHS as period for cycle
clock (32 µs with 4 MHz high speed clock
signal )
CALIBRATE
Enables/disables calibration calculation in the 0 = calculation of calibrated results off
ALU
(allowed only in measurement mode 1)
1 = calculation of calibrated results on
(recommended)
NO_CAL_AUTO
(DisAutoCal)
Enables/disables auto-calibration run in the
TDC
0 = auto-calibration after measurement
1 = auto-calibration disabled
MESSB2
(MRange2)
Switch to measurement mode 2
0 = measurement mode 1
1 = measurement mode 2
NEG_STOP2
Negation stop 2 input
0 = non-inverted input signal – rising edge
1 = inverted input signal – falling edge
NEG_STOP1
Negation stop 1 input
0 = non-inverted input signal – rising edge
1 = inverted input signal – falling edge
NEG_START
Negation start input
0 = non-inverted input signal – rising edge
1 = inverted input signal – falling edge
ID0
Free bits, e.g. to be used as identification or
version number
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3-5
Ultrasonic-Flow-Converter
TDC-GP21
Register 1 (address 1):
31
30
29
28
27
HIT2
0
1
26
25
24
23
22
21
HIT1
0
1
0
1
0
20
19
18
HITIN2
1
0
1
0
0
17
16
15
14
HITIN1
0
0
0
0
0
0
13
12
8
7-0
SEL_TSTO2
SEL_TSTO1
ID1
0
0
0
0
11
0
10
9
0
0
Parameter
Description
Settings
HIT2
Defines operator for ALU data postprocessing
Measurement mode 1: HIT1-HIT2
Measurement mode 2: HIT2-HIT1
Measurement
mode 1:
0 = Start
1 = 1. Stop Ch1
2 = 2. Stop Ch1
3 = 3. Stop Ch1
4 = 4. Stop Ch1
5 = no action
6 = Cal1 Ch1
7 = Cal2 Ch1
9 = 1. Stop Ch2
A = 2. Stop Ch2
B = 3. Stop Ch2
C = 4. Stop Ch2
Measurement
mode 2:
2 = 1. Stop Ch1
3 = 2. Stop Ch1
4 = 3. Stop Ch1
HIT1
Defines operator for ALU data postprocessing
Measurement mode 1: HIT1-HIT2
Measurement mode 2: HIT2-HIT1
Measurement
mode 1:
0 = Start
1 = 1. Stop Ch1
2 = 2. Stop Ch1
3 = 3. Stop Ch1
4 = 4. Stop Ch1
5 = no action
6 = Cal1 Ch1
7 = Cal2 Ch1
9 = 1. Stop Ch2
A = 2. Stop Ch2
B = 3. Stop Ch2
C = 4. Stop Ch2
Measurement
mode 2:
1 = Start
EN_FAST_INIT
Enables fast init operation
0 = Fast init mode disabled
1 = Fast init mode enabled
HITIN2
Number of expected hits on channel 2
0
1
2
3
4
5
3-6
= stop channel 2 disabled
= 1 hit
= 2 hits
= 3 hits
= 4 hits
to 7 = not permitted
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TDC-GP21
HITIN1
Number of expected hits on channel 1
0
1
2
3
4
5
= stop channel 1 disabled
= 1 hit
= 2 hits
= 3 hits
= 4 hits
to 7 = not permitted
CURR32K
Low current option for 32 kHz oscillator.
Basically there is no need to use high current
option (1). Low current (0) also guarantees
oscillation.
0 = low current (recommended)
1 = high current (GP2 compatibility)
SEL_START_FIRE
Fire pulse is used as TDC start. The START
input is disabled.
0 = TDC-GP2 behavior
1 = Use FIRE as Start
SEL_TSTO2
Defines functionality of EN_START pin.
Besides the GP2 functionality this pin can act
as output for various signals. If SEL_TSTO2 >
0 then EN_START = HIGH internally.
0 = GP2 functionality, High level enables
the START pin.
1 = START_TDC output
2 = STOP1 TDC output
3 = STOP2 TDC output
4 = Stop Temperature measurement
output
5 = “0” indicates TOF_DOWN being active,
“1” indicates TOF_UP being active
6 = n.c.
7 = 4 kHz (32 kHz/8) clock
SEL_TSTO1
Defines functionality of FIRE_IN pin. Besides
the GP2 functionality this pin can act as
output for various signals. If SEL_TSTO1 >1
the FIRE_IN is connected to GND internally.
0 = GP2 functionality, FIRE_IN input for
sing-around
1 = START_TDC output
2 = STOP1 TDC output
3 = STOP2 TDC output
4 = Start Temperature measurement
output
5 = EN_STOP by DELVAL output
6 = Comparator out
7 = 32 kHz clock
ID1
Free bits, e.g. to be used as identification or
version number
Register 2 (address 2):
31
30
29
28
27
26
25
24
23
22
21
20
19
EN_INT[2:0]
0
0
1
18
17
16
15
14
13
12
11
10
9
8
DELVAL1
0
0
0
0
0
0
0
0
0
0
0
0
0
ID2
0
0
0
0
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7-0
0
0
0
3-7
0
0
Ultrasonic-Flow-Converter
TDC-GP21
Parameter
Description
Settings
EN_INT[2:0]
Activates interrupt sources wired by OR.
Additional bit in register 6 (see there, too)
Bit 31 = Timeout interrupt enable
Bit 30 = End Hits interrupt enable
Bit 29 = ALU interrupt enable
Reg6, BIT21 = End of EEPROM action
RFEDGE2
Edge sensitivity channel 2
0 = rising or falling edge
1 = rising and falling edge
RFEDGE1
Edge sensitivity channel 1
0 = rising or falling edge
1 = rising and falling edge
DELVAL1
Delay value for internal stop enable unit, hit 1
channel 1. Fixed point number with 14
integer and 5 fractional digits in multiples of
Tref
DELVAL1 = 0 to 16383.96875
ID2
Mandatory: If EN_ANALOG = 0 then set
DELVAL1 = 0
Free bits, e.g. to be used as identification or
version number
Register 3 (address 3):
31
30
29
28
27
26
25
24
23
22
21
20
19
k.d.
0
0
18
17
16
15
14
13
12
11
10
8
DELVAL2
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Description
Settings
EN_ERR_VAL
Timeout forces ALU to write ‘hFFFFFFFF
into the output register
0 = disabled
1 = enabled
SEL_TIMO_MB2
Select predivider for timeout in
measurement mode 2
0 = 64 µs
1 = 256 µs
2 = 1024 µs
3 = 4096 µs recommended
@ 4 MHz ClkHS
DELVAL2
Delay value for internal stop enable unit, hit DELVAL2 = 0 to 16383.96875
2 channel 1. Fixed point number with 14
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7-0
ID3
Parameter
3-8
9
0
0
0
TDC-GP21
integer and 5 fractional digits in multiples
of Tref
ID3
Mandatory: If EN_ANALOG = 0 then set
DELVAL2 = 0
Free bits, e.g. to be used as identification
or version number
Register 4 (address 4):
31
30
29
28
27
26
25
24
23
22
21
20
19
k.d.
0
0
1
18
17
16
15
14
13
12
11
10
9
8
DELVAL3
0
0
0
0
0
0
0
0
0
0
0
0
0
ID4
0
0
0
0
0
0
Parameter
Description
Settings
DELVAL3
Delay value for internal stop enable unit, hit 3
channel 1. Fixed point number with 14
integer and 5 fractional digits in multiples of
Tref
DELVAL3 = 0 to 16383.96875
ID4
7-0
0
0
0
Mandatory: If EN_ANALOG = 0 then set
DELVAL3 = 0
Free bits, e.g. to be used as identification or
version number
Register 5 (address 5):
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
PHFIRE
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
ID5
0
0
0
0
0
0
0
Parameter
Description
Settings
CONF_FIRE
Output configuration for pulse generator
3’b 011 is not allowed
Bit 31 = 1: FIRE_BOTH (inverts FIRE_DOWN)
Bit 30 = 1: enable output FIRE_UP
Bit 29 = 1: enable output FIRE_DOWN
EN_STARTNOISE
Enables additional noise for start channel
1 = switch on noise unit
DIS_PHASESHIFT
(Dis_PhaseNoise)
Phase noise unit. Improves statistics and
should be enabled if start pulse
generation is derived from the GP2
reference clock (e.g. with fire pulse
generator).
1 = disables phase noise
0 = enables phase noise unit
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7-0
3-9
0
Ultrasonic-Flow-Converter
REPEAT_FIRE
TDC-GP21
Number of pulse sequence repetition for
"quasi-sing-around"
PHFIRE
Enables phase reversing for each pulse of
a sequence of up to 15 possible pulses.
PHFIRE[0..14] are available.
ID5
Free bits, e.g. to be used as identification
or version number
0=
1=
2=
...
7=
no signal repetition
1 signal repetition
2 signal repetition
7 signal repetition
0 = no inversion, phase jump HIGH-LOW
1 = inversion, phase jump LOW-HIGH
Bit 23 = 0 (mandatory)
Register 6 (address 6):
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7-0
ID6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Parameter
Description
Settings
EN_ANALOG
Activates the analog part for the ultrasonic
flow measurement is. If active, this section is
powered only for the duration of the
measurement to save current. STOP1 and
STOP2 are analog inputs now and
automatically selected by the internal
multiplexer.
0 = STOP1 and STOP2 are digital inputs
(TDC-GP2 compatibility)
1 = The analog section is used.
Mandatory:
If EN_ANALOG = 0 then set DELVAL1 =
DELVAL2 = DELVAL3 = 0
NEG_STOP_TEMP Inverts the SenseT input signal. This is
mandatory when the internal comparator is
used instead of the external one like in TDCGP2
0 = external 74HC14 is used (TDC-GP2
compatibility)
1 = internal Schmitt trigger is used
DA_KORR
7 = 7 mV
3-10
Sets comparator offset from -8 mV to +7
15 = - 1 mV
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0
TDC-GP21
mV. 2‘s complement
6 = 6 mV
...
1 = 1 mV
0 = 0 mV
14 = - 2 mV
9 = - 7 mV
8 = - 8 mV
TW2
Timer to charge up the capacitor of the
recommend RC network when the internal
analog part is used.
Charge time:
0 = 90 µs
1 = 120 µs
2 = 150 µs
3 = 300 µs, recommended setting
EN_INT[3]
Additional interrupt source. See also register
2 for the lower 3 bits of EN_INT. The various
sources are wired by an OR. An EEPROM
action, e.g. EEPROM_COMPARE, is managed
by the TDC-GP21 and especially the EEPROM
write may last up to 130ms. Indicating the
end will be helpful.
1 = end of EEPROM action
START_CLKHS[2]
Highest bit to set the settling time for the
high speed oscillator. The lower bits are set
in register 0, bit 18 and 19.
0
1
2
3
4
5
= off
= continuously on
= 480 µs delay
= 1.46 ms
= 2.44 ms
to 7 = 5.14 ms
CYCLE_TEMP
Selects timer for triggering the second
temperature measurement in multiples of
50/60Hz
0
1
2
3
=
=
=
=
1
1.5
2
2.5
CYCLE_TOF
Selects timer for triggering the second ToF
measurement in multiples of 50/60Hz
0
1
2
3
=
=
=
=
1
1.5
2
2.5
HZ60
TDC-GP21 can make complete up and down
flow measurement and also two temperature
measurements in series. The time interval
between 2 measurements is based on 50 or
60 Hz.
0 = 50 Hz base, 20 ms
1 = 60 Hz base, 16.67ms
FIREO_DEF
Specifies the default level of the inactive fire
buffer. Example: if FIRE_UP is active then the
FIRE_DOWN buffer is connected to the
default level. Setting 1 is mandatory when
using the integrated analog section.
0 = High-Z (as in GP2)
1 = LOW
QUAD_RES
Option to improve the resolution by factor 4
from 90 ps to 22 ps. Can be used only in
measurement mode 2.
0 = off (TDC-GP2 mode)
1 = on
DOUBLE_RES
Doubles the resolution from 90 ps to 45 ps.
In measurement mode 1 this option limits the
number of stop inputs to one (Stop1)
0 = off (TDC-GP2 mode)
1 = on
TEMP_PORTDIR
Ports for temperature measurement are
measured in the opposite order.
0 = PT1 > PT2 > PT3 > PT4
1 = PT4 > PT3 > PT2 > PT1
ANZ_FIRE[6:4]
Highest 3 bits of the number of fire pulses.
See also register 0. If ANZ_FIRE > 15 then
0 = off
1 = 1 pulse
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3-11
Ultrasonic-Flow-Converter
TDC-GP21
PHFIRE is no longer active.
ID6
2 = 2 pulses
…
127 = 127 pulses
Free bits, e.g. to be used as identification or
version number
3.2
Read registers
The result and status registers can be read by means of opcode ’hB x. The opcode is
followed by 4, 2 or 1 bytes, depending on the address.
The ID register bits in the configuration registers can be read back by means of opcode
’hB7. This opcode is followed by 7 bytes in the order ID0, ID1 ... ID6, each byte with the
MSB first.
Table 3-2: Read Registers
Symbol
Bits
Description
0
RES_0
32
Measurement result 1, fixed-point number with 16 integer and 16 fractional
digits
2 15
2 0 , 2 -1
2 -16
1
RES_1
32
Measurement result 2, fixed-point number with 16 integer and 16 fractional
digits
2
RES_2
32
Measurement result 3, fixed-point number with 16 integer and 16 fractional
digits
3
RES_3
32
Measurement result 4, fixed-point number with 16 integer and 16 fractional
digits
4
STAT
16
15
5
3.2.1
REG_1
8
13
12
11
10
9
8 - 6
5 - 3
2 - 0
Error
short
Error
open
Timeout
Precounter
Timeout
TDC
# of
hits
Ch 2
# of
hits
Ch 1
ALU_
OP_
PTR
EEPROM_Error
14
EEPROM_DED
EEPROM_eq_CREG
ADR
Content of highest 8 bits of write register 1, to be used for testing the
communication
Result Registers
The data structure and the occupancy of the result registers depend on the operatio n
mode and whether calibrated or non-calibrated data are stored. Several cases must be
distinguished:
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Only in measurement mode 1 negative results are possible.
In measurement mode 2 only positive results are possible, given as unsigned numbers.
A non-calibrated measure is possible only in measurement mode 1.
In measurement mode 1 with calibrated data (ALU) the time intervals that have to be
measured can not exceed twice the period of the calibration clock. When measuring
bigger time intervals an ALU - overflow will occur and ’hFFFFFFFF is written in the
appropriate result register.
a. Measurement mode 1 with calibrated data (CALIBRATE = 1)
The results are given in multiples of the internal reference clock (= external reference
clock divided by 1, 2 or 4 (DIV_CLKHS)). Calibrated data are 32 bit fixed point numbers
with 16 integer bits and 16 fractional bits. Any calibrated result covers therefore 1 result
register. The serial output begins with the highest bit (2 15 ) and ends with the lowest one
(2 -16 ). The numbers are available in complements of 2.
Time = RES_X * T ref * 2
Time < 2 * T ref * 2
DIV_CLKHS
= RES_X * T ref * N , with N = 1, 2 or 4
DIV_CLKHS
b. Measurement mode 1 without calibration (CALIBRATE = 0)
Non-calibrated data are of the type ‘Signed Integer’ and are stored as a 16 bit value in the
high word of the result registers. The bits of the low word are set to zero. The result is
represented as number of LSB and is available in complements of 2.
Time = RES_X * LSB ~ RES_X * 90 ps
c. Measurement mode 2
In measurement mode 2 the TDC-GP21 only supports calibrated measurement. The
results are given in multiples of the internal reference clock (= external reference clock
divided by 1, 2 or 4 (DIV_CLKHS)). Calibrated data are 32 bit fixed point numbers with 16
integer bits and 16 fractional bits. Any calibrated result covers therefore 1 result register.
The serial output begins with the highest bit (2 15 ) and ends with the lowest one (2 -16 ). The
numbers are available in complements of 2.
Time = RES_X * T ref * 2
DIV_CLKHS
= RES_X * T ref * N , with N = 1, 2 or 4
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d. Temperature measurement
Discharge time in the same format as in c., measurement mode 2.
The ratio of the discharge times equal the ratio of resistance:
R T = R ref *  T / ref
3.2.2
Status Register
Table 3-3: Status registers
Bits
Name
Description
Values
2 – 0
ALU_OP_PTR
ALU operation pointer. Pointer to the result register.
See description below
5 – 3
# of hits Ch 1
Number of hits registered on channel 1
8 – 6
# of hits Ch 2
Number of hits registered on channel 2
9
Timeout TDC
Indicates an overflow of the TDC unit
1 = overflow
10
Timeout Precounter
Indicates an overflow of the 14 bit precounter in MR 2
1 = overflow
11
Error open
Indicates an open sensor at temperature
measurement
1 = open
12
Error short
Indicates a shorted sensor at temperature
measurement
1 = short
13
EEPROM_Error
Single error in EEPROM which has been corrected
1 = error
14
EEPROM_DED
Double error detection. A multiple error has been
detected which can not be corrected.
1 = multiple
error
15
EEPROM_eq_CREG
Indicates whether the content of the configuration
registers equals the EEPROM
1 = equal
ALU Operation Pointer
Description: The ALU operation pointer is stored in bits 0-2 of the status register (range
of 0x00 to 0x03) and provides an index to one of the 4 results registers (R ES_0 to RES_3)
as follows:
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3.3
EEPROM
The TDC-GP21 has a 7x32 bit EEPROM. This EEPROM can be used to store the
configuration data together with the ID or version number. Only the following three actions
are possible:

Write configuration register content into the EEPROM

Transfer the EEPROM content into the configuration registers

Compare the configuration registers‘ content with the EEPROM content
Important Note:
If values are to be stored in the EEPROM it is mandatory to ensure that NO measurement is
running (neither ToF nor temperature nor calibration measurements). During measurement a
write access to the EEPROM is not permitted. The write access to the EEPROM takes about
300 ms. With no consideration, the EEPROM may be written with incorrect values. It may even
happen that adjustment values are overwritten which prevents proper operation of the TDC.
Besides the ID it is not possible to read back the EEPROM. This gives customers the
possibility to program the chips by themselves and prohibit other to read back the
configuration.
For verification it is possible to compare the configuration register may be compare with
the EEPROM. Bit EEPROM_eq_CREG in the status register indicates whether the content is
equal or not.
The EEPROM has an internal error correction (Hamming code). It is possible

to detect and correct single bit errors,

to detect multi-bit errors without correction
Errors are indicated in the status register, bits EEPROM_Error (single bit) and
EEPROM_DED (double error detection).
*****With each read access/compare to the EEPROM the error bit is checked. In case
a single bit error is detected a refresh cycle is started automatically and the data is
restored.
The data retention of the EEPROM is > 10 years @ 85 °C without single or multiple
errors. With regular Compare_EEPROM commands (e.g. once per month) the data
retention can be extended unlimited.
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3.4
TDC-GP21
SPI-interface
The serial interface is compatible with the 4-wire SPI standard. It needs the
SerialSelectNot (SSN) and can not operated as 3-wire interface.
SSN
- Slave Select
SCK
- SPI Clock
SI
- SPI Data In
SO
- SPI Data Out
The TDC-GP21 does only support the following SPI mode (Motorola specification) * :
Clock Phase Bit = 1
Clock Polarity Bit = 0
SCK starts with LOW, data take over is with the falling edge of SCK. The timings are
shown in section 2.3. The interrupt pin is set back to INTN = 1 if:

SSN goes LOW

or, in case SSN is already LOW, with the first rising edge of SCK.
SSN as Reset
The SerialSelectNot (SSN) line is the HIGH-active reset for the serial interface. After SSN
is set to LOW different operations can be addressed, not depending on the status of the
interface before the reset.
Note:
It is mandatory to set the SSN – line to High-state for at least 50 ns between each
Read-/Write sequence.
* There is no common SPI specification, especially for phase & polarity. Some microcontroller may
need a different setting, e.g. MSP430 run with Clock Phase = Clock Polarity = 0
Opcodes
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Table 3-4: Opcodes
Hex
MSB
LSB
Description
Followed by
New
’h8x
1
0
0
0
0
A2 A1 A0 Write into address A
24 bit or
32 bit data
’hBx
1
0
1
1
0
A2 A1 A0 Read from address A
8, 16 or 32
bit data
’hB7
1
0
1
1
0
1
1
1
Read ID bit
56 bit ID‘S
’hC0
1
1
0
0
0
0
0
0
Write configuration
registers into EEPROM
x
’hF0
1
1
1
1
0
0
0
0
Transfer EEPROM content
into configuration
registers
x
’hC6
1
1
0
0
0
1
1
0
Compare configuration
registers with EEPROM
x
’h70
0
1
1
1
0
0
0
0
Init
’h50
0
1
0
1
0
0
0
0
Power On Reset
’h01
0
0
0
0
0
0
0
1
Start_TOF
’h02
0
0
0
0
0
0
1
0
Start_Temp
’h03
0
0
0
0
0
0
1
1
Start_Cal_Resonator
’h04
0
0
0
0
0
1
0
0
Start_Cal_TDC
’h05
0
0
0
0
0
1
0
1
Start_TOF_Restart
x
’h06
0
0
0
0
0
1
1
0
Start_Temp_Restart
x
x
The transfer starts with the MSB and is finished sending the LSB. The transfer is done
bytewise. Data transfer can be stopped after each byte, sending a LOW-HIGH-LOW on the
SSN line.
Example:
‘h80 + 3 bytes will write configuration register 0 in the TDC-GP2 compatible mode.
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‘h80 + 4 bytes will write configuration register 0 including IDO (TDC -GP21 only).
It is not possible to do incremental writing. Each register must be addressed separately.
3.4.1

Opcode Explanations
’hC0, ’hF0, ’hC6 all refer to EEPROM operations. Those may last up 130 ms,
especially the EEPROM write. Therefore, the EN_INT bit 3 in register 6 indicates
the end of the EEPROM operation. This can be used to adjust microprocessor
actions.

’h01, Start_TOF: triggers a sequence for a single time-of-flight measurement. First,
the 4 MHz oscillator is switched on. After the delay set to settle the oscillator
(START_CLKHS), the comparator and the reference voltage are switched on. The
receiver capacitor is charged up th Vref while inactive fire buffer is pulled down to
GND. After the delay set to charge up the capacitor (TW2), the fire buffer sends
the fire pulses. After the delay set in DELVAL the TDC stop channel is open. At the
end of the measurement the analog section and the 4 MHz are switched off and
the current consumption drops down to near zero. The interrupt is set, pin INTN =
LOW.

’h05, Start_TOF_Restart: This opcode runs the Start_TOF sequence twice, in up
and down direction as it is typical in ultrasonic flow meters. The interrupt is set, pin
INTN = LOW, when the time measurement for each direction is finished. So, for
one Start_TOF_Restart command the microprocessor sees two interru pts and has
to read twice. The time interval between the up and down measurement is set by
configuration parameter CYCLE_TOF in multiples of 50 Hz or 60 Hz. The right
selection of the delay between the two measurements suppresses 50/60 Hz noise.

CYCLE_TOF
factor HZ60 = 0(50Hz)
0
1
20 ms 16.67 ms
1
1.5
30 ms 25.00 ms
2
2
40 ms 33.33 ms
3
2.5
50 ms 41.67 ms
HZ60 = 1(60Hz)
’h02, Start_Temp: triggers a single temperature measurement sequence. It begins
with the fake measurements (ANZ_FAKE) on port PT0. Then it measures ports PT0
> PT1 > PT2 > PT4. If TEMP_PORTDIR is set one then the sequence of ports is
inverted, starting with the fake measurements at port PT4.

’h06, Start_Temp_Restart: This opcode runs the Start_Temp sequence twice. The
time interval between the up and down measurement is set by configuration
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parameter CYCLE_TEMP in multiples of 50 Hz or 60 Hz. The right selection of the
delay between the two measurements suppresses 50/60 Hz noise.
CYCLE_TEMP

factor
HZ60 = 0 (50Hz)
HZ60 = 1 (60Hz)
0
1
20 ms
16.67 ms
1
1.5
30 ms
25.00 ms
2
2
40 ms
33.33 ms
3
2.5
50 ms
41.67 ms
’h03, Start_Cal_Resonator: Triggers a calibration measurement of the high speed
oscilator. The TDC measures a time interval between 61 µs and 488 µs, specified
in ANZ_PER_CALRES. The end of the measurement is indicated by the interrupt.
The result, in multiples or the high speed clock period, is stored in result register
0. Dividing this by the theoretical value gives the correction factor.

’h04, Start_Cal_TDC: This command starts a measurement of 2 periods of the
reference clock. It is used to update the calibration raw data. Typically, the chip is
configured for auto-calibration and this command is not necessary.
3.4.2
SPI Sample
Figure 3-1: Sample scope picture for sequence INIT ’h70 and Start_Cal_TDC = ’h04
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4
Converter Frontend
4.1
TDC - Measurement mode 1
4.1.1
General Description

Measurement range from 3.5 ns to 2.4 µs (0 to 2.4 µs between stop channels)

2 stop channels referring to one start channel each of typ. 90 ps resolution

1 stop channel referring to one start channel with typ. 45 ps resolution

20 ns pulse pair resolution

4-fold multihit capability for each stop channel

Selectable rising/falling edge sensitivity for each channel

Enable pins for windowing functionality

The possibility to arbitrarily measure all events against each other

Typical application: Laser ToF, RF ToF, ATE
Digital TDCs use internal propagation delays of signals through gates to measure time
intervals with very high precision. Figure 5 clarifies the princip al structure of such an
absolute-time TDC. Intelligent circuit structures, redundant circuitry and special methods
of layout on the chip make it possible to reconstruct the exact number of gates passed by
the signal. The maximum possible resolution strongl y depends on the maximum possible
gate propagation delay on the chip.
Figure 4.1
The measuring unit is triggered by a START signal and stopped by a STOP signal. Based on
the position of the ring oscillator and the coarse counter the time interval between START
and STOP is calculated with a 20 bit measurement range.
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The BIN size (LSB) is typically 90 ps at 3.3 V and 25 °C ambient temperature. The RMS
noise is about 60 ps (0.7 LSB). The gate propagation delay times strongly depend on
temperature and voltage. Usually this is solved doing a calibration. During such a
calibration the TDC measures 1 and 2 periods of the reference clock.
The measurement range is limited by size of the counter:
t yy = BIN x 26224 ~ 90 ps x 26224 = 2.4 µs
Time (Condition)
Description
t ph
2,5 ns (min.)
Minimum pulse width
t pl
2,5 ns (min.)
Minimum pulse width
t ss
3.5 ns ns (min)
2.4 µs (max.)
Start to Stop
t rr
20 ns (typ.)
Rising edge to rising
edge
t ff
20 ns (typ.)
t va
1.24µs uncalibrated
4.25µs calibrated
t xx
No timing limits
t yy
2.4 µs (max)
Figure 4.2
Last hit to data valid
Max. measurement
range
= 26224 * LSB
Input circuitry
Each input separately can be set to be sensitive to rising or falling edge or both edges.
This is done in register 0, bits 8 to 10. (NEG_START, NEG_STOP 1, NEG_STOP2) and
register 2, bit 27 & 28, RFEDGEx.
Furthermore all Start/Stop-inputs support a high active enable pin.
4.1.2
Measurement Flow
Configuration
At the beginning the TDC-GP21 has to be configured. The main settings for measurement
mode 1 are:
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a. Select measurement mode 1
Set register 0, bit 11, MESSB2 = 0.
Register 6, bit 12, DOUBLE_RES = 1 selects double resolution. With this bit set the
resolution is typ. 45 ps instead of 90 ps, but only one STOP channel is available.
b. Select the reference clock (see also section 5.1)
Register 0, bits 18 & 19 and register 6, bit 20, START_CLKHS defines the switch-on
behavior of the high-speed clock. If only the 32 kHz is used it should be “0“. If only the
high-speed clock is used it should be “1“ (continuously on).
Register 0, bits 20 & 21, DIV_CLKHS
sets an additional internal divider for
the reference clock (1, 2 or 4). This is
important for calibrated
measurements in measurement mode
1 because the ALU works correctly
only if 2*T ref (intern) is bigger than the
maximum time interval to be
measured. Otherwise the ALU output
is ’hFFFFFFFF.
Make also sure that 2*T ref (intern) <
2.4 µs to avoid a timeout during
calibration.
Figure 4.3
c. Set the number of expected hits
In register 1, bits 16 to 18 and 19 to 21, HITIN1 and HITIN2 the user has to define the
number of hits the TDC-GP21 has to wait for. A maximum of 4 on each channel is
possible. The TDC-GP21 measures until the set number of hits is registered or a timeout
occurs.
d. Select calibration
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As the BIN size varies with temperature and voltage the TDC-GP21 ALU can internally
calibrate the results. This option is switched on by setting register 0, bit13, CALIBRATE =
“1“. It is recommended to do this.
For the calibration the TDC measures 1 and 2 cycles of the reference cloc k. The two data
are stored as Cal1 and Cal2.
There are two ways to update the calibration data Cal1 and Cal2:
- Separate calibration by sending opcode Start_Cal_TDC via the SPI interface
- Automatic update by setting register 0, bit 12, NO_CAL_A UTO = “0“. In most applications
this will be the preferred setting.
e. Define ALU data processing
While the TDC unit can measure up to 4 hits on each channel the user is free in his
definition what the ALU shall calculate. The settings are done in register 1, bits 16 to 19
and 20 to 23, HIT1 and HIT2. Both parameters can be set to:
0 = Start
1 = 1. Stop Ch1
9 = 1. Stop Ch2
2 = 2. Stop Ch1
A = 2. Stop Ch2
3 = 3. Stop Ch1
B = 3. Stop Ch2
4 = 4. Stop Ch1
C = 4. Stop Ch2
Examples:
Reg1 = ‘h01xxxx - 1st Stop Ch1-Start
Reg1 = ‘h2Bxxxx - 3rd Stop Ch2-2nd Stop Ch1
6 = Cal1 Ch1
Reg1 = ‘h06xxxx - Cal1
7 = Cal2 Ch1
The ALU calculates HIT1 - HIT2.
In case calibration is active the ALU does the full calibration calculation (except when
reading the calibration values. In this case the ALU writes the Cal1/Cal2 ra w data to the
output register).
(
4-4
)
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Figure 4.4
f. Select input sensitivity
In register 2, bits 27 & 28, RFEDGE1 and RFEDGE2, the user can select whether the stop
inputs are sensitive to either rising or falling edges (RFEDGE = “0“) or to both rising and
falling edges (RFEDGE = “1“).
In register 0, bits 8 to 10 the user can add an internal inverter to each inpu t, Start,
Stop1 and Stop2. With RFEDGE = “0“ this is the same as rising edge (NEG_X = “0“) or
falling edge (NEG_X = “1“).
g. Interrupt behavior
The interrupt pin 8, INT can have different sources. They are selected in register 2, bits
29 to 31, EN_INT and register 6, bit 21.
Reg. 2 bit 29 = “1”
ALU ready
Reg. 2 bit 30 = “1”
The set number of hits is there
Reg. 2 bit 31 = “1”
Timeout of the TDC unit
Reg. 6 bit 21 = “1”
End of EEPROM action
The different options are wired by OR to enable more than one so urce. The first rising
edge of SCK resets the INTN pin (interrupt).
After the configuration the user has to initialize the TDC-GP21 by sending opcode “Init” so
that the TDC accepts Start and Stop hits.
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Measurement
After an initialization the TDC unit will start with the first pulse on the Start input. It will
run until:

the set number of hits has been seen (maximum 4 on both stop channels in mode
1)

or until a timeout occurs at the end of the measurement range (at about 2.4 µs in
mode 1).
The time measurement raw data are internally stored. The number of hits can be seen
from the status register, bits 3 to 8. In case calibration is active the TDC now measures
one and two periods of the internal reference clock (T ref * 1, 2 or 4). The calibration raw
data Cal1 and Cal2 are also internally stored.
Figure 4.5
Data Processing
At the end of the measurement the ALU starts to process the data according to the HIT1,
HIT2 settings and transfers the result to the output register. In case calibration is off the
ALU transfers the 16 bit raw data to the output register. With calibration the ALU
calculates according to 3.1.1.d and transfers the 32 bit fixed point number to the output
register.
The ALU can be switched off configuring HIT1 = HIT2 = 5.
The time it takes the ALU depends on whether calibration is on or not and the supply
voltage.
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Table 4.1: ALU timings
un-calibrated
(disable AutoCal.)
2.5 V
3.0 V
calibrated
1.56 µs
1.24 µs
3.6 V
1.0 µs
Predivider
As soon as the data is available
from the output register the
interrupt flag is set (assumed that
3.0 µs
0
the ALU interrupt is enabled, see
4.58 µs
1
reg. 2, EN_INT). Further the load
7.58 µs
2
2.75 µs
0
4.25 µs
1
7.26 µs
2
2.54 µs
0
4.0 µs
1
7.0 µs
2
pointer of the output register is
increased by 1 and points to the
next free memory. The actual
position of the load pointer can be
seen in the status register, bits 0
to 2.
Reading Data
Example:
Now the user can read the data sending
the opcode 10110ADR. With the next
16 clock cycles (un-calibrated data) or
32 clock cycles (calibrated data) the
TDC-GP21 will send the result, beginning
with the most significant bit (MSB). The
configuration
...
write reg1=’h014400
calculate 1st Stop -Start
...
first rising edge of SCK resets the INTN
Initialize
pin (interrupt).
...
while(Check interrupt flag)
a. Un-calibrated data format:
write reg1=’h024400
16 bit Signed integer in complements of
2. 1BIN = uncalibrated gate delay is
about 90 ps at 3.3 V and 25 °C.
Time = RES_X x 90 ps
4 hits on channel 1,
calculate 2nd -Start
wait(4.6 µs)
write reg1=’h034400
calculate 3rd-Start
wait(4.6 µs)
write reg1=’h044400
calculate 4th-Start
b. Calibrated data format:
wait(4.6 µs)
32 bit fixed-point number in
Now all Hit data are available from registers 0 to 3.
The load pointer value is 4.
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complements of 2. Given in multiples of the reference clock.
Time = RES_X * T ref * N, with N = 1, 2 or 4
The measured time interval may not exceed otherwise the ALU will go into overflow and will
write the data ’hFFFFFFFF to the output register.
The configuration of the ALU allows only one hit calculation at the time. In case mor e than
one hit has been measured it is necessary to write new commands to HIT1/HIT2 to
instruct the ALU for calculating the other hits. After writing to HIT1/HIT2 it is necessary
to wait for minimum t.b.d. µs (calibrated data) or t.b.d. ns (un -calibrated data) before
reading or writing again to HIT1/HIT2.
Reading Calibration Raw Data
The calibration data are not addressed directly after the calibration measurement but
after the next regular measurement, before the next INIT.
Source Code Example:
//-------------------------------------------------------------------------// 1st Measurement plus calibration data readout
gp21_send_1byte(Bus_Type, Init);
// Wait for INT Slot_x
Wait_For_Interrupt(Bus_Type);
// First regular measurement (to readout calibration raw data)
Result = gp21_read_n_bytes(Bus_Type, 4 ,0xB0 ,0x00 ,16);
// readout the new calibration data from result register adr 0x01
gp21_wr_config_reg(Bus_Type, 0x81, 0x67490000);
Diff_Cal2_Cal1 = gp21_read_n_bytes(Bus_Type, 4, 0xB0 ,0x01 ,16);
//--------------------------------------------------------------------------
At the end the TDC-GP21 has to be initialized again to be ready for the next measurement.
This is done by sending the opcode “Init“ so that the TDC accepts new Start and Stop hits.
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4.2
TDC - Measurement mode 2
4.2.1
General Description

1 stop channels referring to one start channel

Typical 22 ps / 45 ps / 90 ps resolution

Measurement range from 700 ns to 4 ms @ 4 MHz

2 x T ref pulse pair resolution

3-fold multihit capability, full-automated calculation

Selectable rising/falling edge sensitivity

Integrated programmable windowing for each single stop with 10 ns precision

Typical application: Ultrasonic flow & heat meter
Digital TDCs use internal propagation delays of signals through gates to measure time
intervals with very high precision (see also measurement mode 1, section 4). In
measurement mode 2 the maximum time interval is extended using a pre-divider. The
resolution in LSB remains unchanged by that. In this mode the high -speed unit of the TDC
does not measure the whole time interval but only time intervals from START and STOP to
the next rising edge of the reference clock (fine-counts). In between the fine-counts the
TDC counts the number of periods of the reference clock (coarse -count).
Figure 4.6
The GP21 converter front end section achieves a quantization BIN of 90 ps (LSB) where
Vcc = 3.3 V and the ambient temperature is at 25 °C. RMS noise accounts for 60 ps (0.7
LSB) of this same result. As gate propagation delay is used for precision interval
measurement it is important to consider that this delay time is directly affected by both
Vcc and temperature. Therefore, using Measurement Mode 2, a calibration is required
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and is done automatically with the right configuration. During calibration the TDC
measures one and two periods of the 4 MHz reference clock.
The calibrated result does not depend on temperature or supply voltage.
The measurement range is limited by size of the coarse counter:
t yy = T ref x 2 14 = 4.1ms @ 4MHz
The time interval between START and STOP is calculated with a 26 bit measurement
range.
Time (Condition)
Description
t ph
2,5 ns (min.)
Minimum pulse width
t pl
2,5 ns (min.)
Minimum pulse width
t ss
2*T ref
Start to Stop @
DIS_PHASESHIFT = 1
t rr
2*T ref
Rising edge to rising edge
t ff
2*T ref
Falling edge to falling edge
t va
4.6 µs (max.)
ALU start to data valid
t yy
4 ms (max)
Max. measurement range
Figure 4.7
Input circuitry
Each input separately can be set to be sensitive to rising or falling edg e. This is done in
register 0, bits 0 to 2. (NEG_START, NEG_STOP1).
Further all Start/Stop-inputs support a high active enable pin.
Note:
In case the Start-Stop interval is less than the lower limit tzz the TDC will ignore more and
more events the smaller it is. In no case there will be wrong results.
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4.2.2
Measurement Flow
Configuration
At the beginning the TDC-GP21 has to
be configured. The main settings for
measurement mode 2 are:
a. Select measurement mode 2
setting register 0, bit 11, MESSB2 = 1
b. Select the reference clock
(see also section 5.1)
In measurement mode 2 the TDC-GP21
needs the high-speed clock for the time
measurement. In case of low-power
applications this clock can be switched
of in between measurements. The a
Figure 4.8
32.768 kHz clock is necessary for the
timing control during the oscillator
power-on.
Register 0, bits 18 & 19, START_CLKHS defines the switch-on behavior of the high-speed
clock. If only the high-speed clock is used this is be set to “1“(continuously on). In case
both oscillators are used for current saving reasons this should be set to “2“ for ceramic
oscillators and to “3“ for quartz oscillators.
Register 0, bits 20 & 21, DIV_CLKHS sets an additional internal divider for the reference
clock (1, 2 or 4). The choice has an influence on the minimum time interval
t min = 2 * T ref * 2
DIV_CLKHS
and the maximum time interval
t max = 2 14 * T ref * 2
DIV_CLKHS
Further, it is necessary that
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2 * T ref * 2
DIV_CLKHS
TDC-GP21
< 2.4 µs.
Otherwise the ALU will go into an overflow during calibration and write ’hFFFFFFFF as
output data.
Please note:
The resulting clock after the predivider has to be in the allowed range of 2 MHz to 8 MHz
in single and double resolution and from 2 MHz ... 6 MHz in quad resolution.
c. Set the number of expected hits
In register 1, bits 16 to 18, HITIN1 the user has to define the number of hits the TDC GP21 has to wait for. A maximum of 3 on channel 1 is possible. The number HITIN1
always has to be higher by 1 than the number of expected hits. The reason is that the
Start is also counted as a hit. The TDC-GP21 measures until the set number of hits is
registered or a timeout occurs. register 1, bits 19 to 21, HITIN2 have to be set to “0“.
Example:
2 stop pulses are expected:
HITIN1 = “3”, HITIN2 = “0”
d. Select calibration
The calibration is switched on by setting register 0, bit13, CALIBRATE = “1“. It is
mandatory to do this.
For the calibration the TDC measures 1 and 2 cycles of the reference clock. The two d ata
are stored as Cal1 and Cal2.
There are two ways to update the calibration data Cal1 and Cal2:

Separate calibration by sending opcode Start_Cal_TDC via the SPI interface

Automatic update by setting register 0, bit 12, NO_AUTO_CAL = “0“. In most
applications this will be the preferred setting.
e. Define ALU data processing
While the TDC unit can measure up to 3 hits the ALU can calculate only one hit at once.
The settings are done in register 1, bits 24 to 27 and 28 to 31, HIT1 and HIT2. The
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Start pulse is internally handled like a Stop pulse because of the special measuring method
in measurement mode 2.
Reg1 = ’h21xxxx = Calculate 1st Stop Ch1-Start
Reg1 = ’h31xxxx = Calculate 2nd Stop Ch1-Start
Reg1 = ’h41xxxx = Calculate 3rd Stop Ch1-Start
The ALU calculates the time interval as:
(
)
f. Select input sensitivity
In register 2, bits 27 & 28, RFEDGE1 and RFEDGE2, the user can select whether the stop
inputs are sensitive to either rising or falling edges (RFEDGE = “0“) or to both rising and
falling edges (RFEDGE = “1“). In register 0, bits 8 to 10 the user can add an internal
inverter to each input, Start, Stop1 and Stop2. With RFEDGE = “0“ this is the same as
rising edge (NEG_X = “0“) or falling edge (NEG_X = “1“).
g. Interrupt behavior
The INT pin can have various sources, to be selected in regi ster 2, bits 21 to 23, EN_INT,
and register 6 bit 21 EN_INT.
EN_INT =
no bits set
no Interrupt source
reg2 bit 29
ALU ready
reg2 bit 30
The set number of hits is there
reg2 bit 31
Timeout of the TDC unit
reg6 bit 21
EEPROM action has finished
The different options are wired by OR. The first rising edge of SCK resets the INTN pin
(interrupt).
After the configuration the user has to initialize the TDC-GP21 by sending opcode “Init“ so
that the TDC accepts Start and Stop hits.
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Measurement
After an initialization the TDC unit will start with the first pulse on the Start input. It will
run until:

the set number of hits has been seen (maximum 3 on channel 1 in measurement
mode 2)

or until a timeout occurs. The timeout can be programmed in multiples of the
reference clock setting reg. 3, bits 27 & 28, SEL_TIMO_MB2. At 4 MHz the values
are:
SEL_TIMO_MB2 (@ 4 MHz, DIV_CLKHS = 0)
= 0
= 64 µs
= 1
= 256 µs
= 2
= 1024 µs
= 3
= 4096 µs recommended
At the end of the time measurement the TDC measures 2 periods of the reference clock
for calibration.
Data processing
At the end of the measurement the ALU starts to process t he data according to the HIT1,
HIT2 settings and transfers the result to the output register. The ALU calculates
according to 4.2.2.e and transfers the 32 bit fixed point number to the output register.
The time it takes the ALU depends on the supply voltage to be calculated:
Table 4-2: ALU timings
First Event (1 Hit)
2.5 V
3.0 V
3.6 V
3.7 µs
3.3 µs
3.1 µs
As soon as the data is available from the output register the interrupt flag is set (assumed
that the ALU interrupt is enabled, see reg. 2, EN_INT). Further the load pointer of the
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output register is increased by 1 and points to the next free memory. The actual position
of the load pointer can be seen in the status register, bits 0 to 2.
Reading Data
Now the user can read the data sending the opcode 1 0110ADR. With the next 32 cycles
(calibrated data) the TDC-GP21 will send the result, beginning with the main significant bit
(MSB).
The 32 bit fixed-point numbers in complements of 2 represent the time interval in
multiples of the reference clock.
Time = RES_X * T ref * 2
DIV_CLKHS
Now all hit data are available from registers 0 to 2. The load pointer value is 3.
At the end the TDC-GP21 has to be initialized again to be ready for the next measurement.
This is done by sending the opcode “Init“ so that the TDC accepts new Start and Stop hits.
The first rising edge of SCK resets the INTN pin (interrupt).
4.2.3
Stop Masking
The TDC-GP21 can set time-based masking windows for each of the 3 hits on Stop1 input
when no hits are accepted. The masking refers to the st art event and has an accuracy of
less than 10 ns.
The internal enable unit is connected to the external enable pin by a logical AND. The
external enable pin must be set to “1” to use the internal masking unit. The configuration
settings are made in registers 2 to 4, DELVAL1, DELVAL2 and DELVAL3:

DELVAL1 … DELVAL3 are fixed point numbers with 14 bit integer and 5 bit
fractional digits, in multiples of the internal reference clock
Delay min = DELVALX / 2 5 * T ref * 2
DIV_CLKHS

The minimum mask size is 3 clock cycles

The mask values must have an ascending order. Each mask value must be 3 clock
cycles bigger than the previous value
It is mandatory that if not all registers are used the mask values that are not required are
set to “0”. When all DELVAL registers are set to 0, the complete unit is disabled.
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Example:
4 MHz reference, DIV_CLKHS = 1
DELVAL1 = ’h3200 1st Stop not accepted before 200 µs after Start
(12800/32 * 250 ns * 2 1 = 200 µs)
DELVAL2 = ’h3300 2nd Stop not accepted before 204 µs after Start
(13056/32 * 250 ns * 2 1 = 204 µs)
DELVAL3 = ’h3400 3rd Stop not accepted before 208 µs after Start
(13312/32 * 250 ns * 2 1 = 208 µs)
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4.3
Analog Input Section
Compared to TDC-GP2, the TDC-GP21 has an additional analog input section which can be
used alternatively to the pure digital inputs. Especially the design of ultrasonic flow and
heat meters is greatly simplified by this new option. The external circuit of the ultrasonic
part is reduced to just two resistors and capacitors additional to the piezo transducers.
The ultrasonic signals will be packages of sinusoidal oscillat ions with several 100 mV
amplitude. The signals are coupled to the inputs by means of a high pass filter as the
comparator can not handle GND as threshold. The threshold of the comparator is set to
1/3 Vcc. An analog multiplexer selects the input according to the active mea surement
direction. The comparator is chopper stabilized to guarantee a low offset voltage in the
range of < 2 mV. This is mandatory for a good measurement quality. The input offset
voltage of the comparator is frequently corrected by an internal chopper circuit. If
temperature or supply voltage changes over time, the offset voltage is automatically
adapted and holds at < 2 mV.
All elements are controlled by the TDC-GP21 control unit. They are powered only during
the measurement to keep down the power consumption.
A measurement sequence, triggered by command Start_TOF_Restart looks like the
following procedure, starting with the up flow measurement:

The 4 MHz oscillator is switched on. The chip waits for the programmed delay to
give enough time for the oscillator to reach the full amplitude.

The comparator, the reference voltage and the analog switches get powered.

The capacitor of the transmitting path (STOP1) is connected to GND.

The fire down buffer (FIRE_DOWN) is connected to GND.

The capacitor of the receiving path (STOP2) is charged up to Vref. The TDC waits
the delay set in TW2.

The analog switch selects STOP2 input as input to the comparator.

FIRE_UP is selected as TDC START signal.

The set number of pulses is sent through the fire up buffer, pin FIRE _UP.

The analog signal at STOP2 passes the comparator converted to a digital signal
that is connected to the STOP input of the TDC unit.

When the delay of the stop masking unit (DELVAL) expired the TDC is ready to
measure. It can measure up to 3 stops.
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Figure 4.9

At the end of the measurement the control unit switches off the comparator, the
reference the analog switches and the 4 MHz. The current is reduced to close
zero. The interrupt flag is set.

The control unit waits a period, given in multiples of 50Hz/60Hz. During this the
processor has to read the results.

4-18
After the delay the same procedure is started but in the opposite direction.
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4.3.1
Offset Setting / First Hit Detection
The offset of the comparator can be set in steps of 1 mV from -8mV to +7 mV by means
of parameter DA_KORR, bits 25 to 28 in register 6. DA_KORR is set as 2‘s complement.
This feature can be used to savely detect the first hit. By setting the offset to e.g. +5mV
the rising edge of the first pulse can be savely detected. With this i nformation the stop
making (DELVAL) can be set appropriately. The offset can be set back to 0 mV and with
the next measurement the zero crossing of the 7th wave can be savely detected.
Figure 4-10: First hit detection
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4.4
TDC-GP21
Temperature Measurement
Especially for heat meter applications the TDC-GP21 has a PICOSTRAIN based
temperature measuring unit that offers high resolution and very low current consumption.
The measurement is based on measuring discharge times. Therefore, a capacitor is
discharged alternately through the sense resistors and the reference resistors. As an
improvement compared to TDC-GP2, the TDC-GP21 has the comparator already
integrated.
Figure 4.11:
Figure 4-12: With internal Schmitt trigger
4-20
Figure 4-13: GP2 compatible with external
trigger
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The unit has 4 resistor ports, two of them to be used for the temperature sensors for hot
water (up) and cold water (down). The other two ports are used for reference resistors.
Basically, on reference resistor connected to both ports is suffic ient.
The temperature sensors should have a minimum resistance of 500 Ohm. The cable
length should not exceed 3 m. TDC-GP21 can measure 2-wire sensors only. It is not
possible to use 4-wire sensors. The precision of the temperature measurement is far
within the limits of the standard for heat meters when PT500 or PT1000 are used. In
combination with PT500 or PT1000 temperature sensors there is no need for two
reference resistors. A typical setup with one fixed reference is shown in figure 4 -14.
The EMC protection is a recommendation of acam from experience. Further information
will be shown in section 5.5 EMC Measures.
2 x PT500 / PT1000
100nF
LoadT
down
up
SenseT
Rref
PT1
PT2
TDC-GP21
PT3
PT4
1nF
1nF
EMC protection
Figure 4.14: PT500 / PT1000 temperature measurement with one reference resistor
The temperature measurement is fully automated. It is triggered by the µC sending the
opcodes Start_Temp or Start_Temp_Restart. With Start_Temp_Restart the TDC -GP21
measures the temperature twice, with a delay given in multiples of the 50 Hz/60 Hz
period. This will be of help to reduce 50Hz/60Hz noise.
For a measurement, the TDC-GP21 starts with 2 or 8 dummy measurements at port PT1
before it makes the real four measurements in the order PT1 > PT2 > PT3 > PT4. After
the 4 measurements have finished the interrupt flag is set. TDC -GP21 has the possibility
to inverse the order, making the dummy measurements at port PT4.
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The four data are found in registers 0 to 3. From Res_3/RES_1 and RES_4/RES_2 the
microcontroller can calculate the ratio Rtemp/Rref. By means of a look -up table it can
calculate the temperature for the special type of sensor in use.
Configuration
Register 0, bit 15, ANZ_FAKE sets the number of dummy measurements at the beginning
of a temperature measurement. This is necessary to overcome mechanical effects of the
load capacitor.
ANZ_FAKE = 0
2 dummy measurements
ANZ_FAKE = 1
7 dummy measurements
Register 0, bit 16, T
CYCLE sets the cycle time for the temperature measurement.
TCYCLE = 0
128 µs cycle time @ 4MHz
TCYCLE = 1
512 µs cycle time @ 4MHz
Register 0, bit 17, ANZ_PORT sets the number of ports that will be used.
ANZ_PORT = 0
2 ports = 1 sensor
ANZ_PORT = 1
4 ports = 2 sensors
Register 6, bit 11, TEMP_PORTDIR sets the order of the port measurements
TEMP_PORTDIR = 0
PT1 > PT2 > PT3 > PT4
TEMP_PORTDIR = 1
PT4 > PT3 > PT2 > PT1
Register 6, bit 15, HZ60 sets the base frequency for the delay between the up and down
measurements for commands Start_TOF_Restart and Start_Temp_Restart.
HZ60
= 0
50 Hz base
HZ60
= 1
60 Hz base
Register 6, bits 18, 19, CYCLE_TEMP, selects the factor timer for triggering the second
temperature measurement in multiples of 50/60Hz.
CYCLE_TEMP = 0
= 1
4-22
1
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= 2
2
= 3
2.5
Register 6, bit 30, NEG_STOP_TEMP inverts this signal at the SenseT path. This is
mandatory when the internal comparator is used. Without inversion the unit is compatible
to TDC-GP2 operation with an external Schmitt trigger
NEG_STOP_TEMP
= 0
No inversion, TDC-GP2 compatible
= 1
Inversion, mandatory when the internal comparator is used
Recommended Capacitor Values
The discharge time should be about 150 µs. Therefore the capacitor should have the
following value:
PT500:
220 nF
PT1000:
100 nF
Please set TCYCLE = 1 to avoid timeout error.
Recommended Capacitor Type
To get accurate results we recommend capacitor types with very low dC/dU. We
recommend:
C0G types or CfCap Series from Tayo Yuden
Please do not use X7R or similar capacitors.
Current consumption
By means of the TDC technology the temperature measurement needs an extremely low
current, much less than an A/D converter does.
A full temperature measurement with 2 sensors, 2 references am PT1000 sensor type,
including all calculations takes less than 2.5 µAs. With one temperature measurement in
30 seconds (typical for heat meters) the average current consumption is 0.08 µA only.
This is about 50 times less than other solutions. A PT500 sensor doubles the current.
Note: During temperature measurement the start input has to be enabled.
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Error detection
Additionally the temperature unit checks the plausibility of the results. It is able to detect a
short circuit of the sensor or an open sensor. The TDC-GP21 provides in the relevant
output register an error code instead of a measurement value.
1. Short circuit between lines: equivalent to a very short time interval (< 8 x T ref = 2 µs @
4 MHz). The TDC-GP21 writes a ’h0 to the output register of the shorted sensor.
2. Broken sensor/Short circuit against GND: equivalent to no stop signal or timeout. The
TDC-GP21 writes a ’hFFFFFFFF into the output register of the ope n sensor.
Note: Due to a bug it is necessary to have SEL_TIMO_MB2 at 2ms to get a correct
interrupt indication when 512 µs cycle time is selected.
33nF
1: Short circuit between lines: Error short
2: Short circuit LoadT against GND: Error open
3: Circuit circuit PT2 against GND: Measurement
at PT1 with half the nominal discharge time as
sensor is in parallel to Rref, result out of
reasonable range
LoadT
2
1
SenseT
Rref
PT1
PT2
3
TDC-GP21
PT3
PT4
Figure 4-15: Short circuit indication
Table 4.4: Analog specification
Symbol
Terminal
Resolution RMS
External Schmitt trigger
PT500
PT1000
PT500
PT1000
17.5
17.5
16.0
16.0
Bit
96
96
dB
0.9960
0.9979
SNR
Absolute Gain 3
4-24
2
Internal Schmitt trigger
0.9912
0.9931
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3.6
V
0.9923
0.9940
0.9962
0.9980
3.0
V
0.9912
0.9931
0.9960
0.9979
2.5
V
0.9895
0.9915
0.9956
0.9979
Gain-Drift vs. Vio
0.25
0.23
0.06
0.04
max. Gain Error
(@ dӨ = 100 K)
0,05%
0,05%
0,02%
< 0.01%
Gain-Drift vs. Temp
0.022
0.017
0.012
0.0082
Absolute Gain
vs. Vio 3
(gain factor)
Gain-Drift vs. Vio
0,08
%/10 K
%/V
Initial Zero Offset
< 20
<10
< 20
< 10
mK
Offset Drift vs. Temp
< 0.05
< 0.03
< 0,012
< 0.0082
mK/ °C
PSRR
1
%/V
>100
dB
All values measured at Vio = Vcc = 3.0 V, Cload = 100 nF for PT1000 and 200 nF for
PT500 (C0G-type)
2
measured with external 74AHC14 Schmitt trigger
3
compared to an ideal gain of 1
Gain error and its mathematical correction
The TDC-GP21 temperature measurement is based on acam’s PICOSTRAIN technology.
Here the resistance variation of an RTD is digitized by means of a high accurate time
interval measurement. According to that, the Schmitt trigger’s delay time introduces a
considerable gain error that results in a gain reduction compared to an ideal output value.
This gain reduction can be mathematically described as a deviation from an ideal straight
line. Hence, a simple mathematical correction by adding a correction factor compensates
for this deviation from the ideal gain. It is calculated as follows:
T corr = T uncorr /gainfactor
with
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T corr : gain corrected temperature result
T uncorr : uncorrected temperature result
gainfactor: gain correction factor, compensates the deviation from an ideal gain of 1
By means of this compensation, the effect of the Schmitt trigger’s delay time can be
reduced to a residual gain error of 0.05 % of F. S. with the internal Schmitt trigger, or
even less in combination with an external 74AHC14 Schmitt trigger.
Three main parameters have to be considered, to select the correct gain factor:

base resistance of the temperature sensor (e.g. PT500, PT1000)

used Schmitt trigger (GP21-internal, external 74AHC14)

GP21 supply voltage
The appropriate gain correction factors are provided in table 4-3 (“Absolute gain vs. Vio”).
Import note:
The gain correction factors for the external Schmitt trigger exclusively refer to the
74AHC14 Schmitt trigger. Other types (e.g. 74HC14) require different gain factors, in
order to ensure a correct compensation. According to that, we strongly recommend to
use a 74AHC14 as external Schmitt trigger.
Example 1:
Application with PT1000 Sensor, GP21 internal Schmitt trigger and 3.0 V supply
voltage. According to table 4.3 a gain factor of 0.9931 has to be selected. The gain
corrected result is calculated then by the following equation:
T corr =T uncorr /0.9931
Example 2:
Application with PT500 Sensor, external 74AHC14 Schmitt trigger and 3.6 V supply
voltage. Table 4-3 now specifies a gain factor of 0.9980. The gain corrected result is
calculated as follows:
T corr = T uncorr /0.9980
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5
Details and Special Functions
5.1
Oscillator
The TDC-GP21 uses up to 2 clock signals depending on the operating mode:

High-speed clock, typically 4 MHz, for calibration and as a predivider for the TDC
measuring unit in measurement mode 2 and for the EEPROM

5.1.1
32 kHz clock signal used for internal timer functions.
High-Speed Oscillator
Generally, the TDC-GP21 needs a high-speed clock for calibration. The recommend value is
4 MHz, the possible range is 2 to 8 MHz (2 to 6 MHz in QUAD_RES mode). When running
in measurement mode 2 the TDC-GP21 needs the high-speed clock signal also as a part of
the time measuring unit. Finally the operations need the high speed clock, too.
The oscillator takes an average current of 200 µA when running all the time. But as it is
needed only during the time measurement, the TDC-GP21 has the capability to control the
on-time by itself. The settings are done with parameter START_CLKHS. With
START_CLKHS > 1 the oscillator is switched on after sending opcodes Start_TOF,
Start_TOF_Restart, Start_Temp and Start_Temp_Restart for the duration of the
measurement. A delay between starting the oscillator and starting the measurement
guarantees sufficient time for the oscillation to settle at full amplitude.
Note:
It is strongly recommended to use a ceramic oscillator. Exactly because a quartz needs
much longer to settle than a ceramic oscillator. This costs a lot current, but using a
quartz oscillator has no advantage.
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START_CLKHS
= 0
Oscillator off
= 1
Oscillator continuously on
= 2
The measurement is started with 480 µs delay.
= 3
same as ‘2’, but with 1.46 ms delay
= 4
same as ‘2’, but with 2.44 ms delay
Figure 5.1
= 5 to 7
same as ‘2’, but with 5.14 ms delay
The programmable delay guarantees that the oscillator has settled before the
measurement starts. For ceramic resonators 480 µs will be sufficient. For quartz the
necessary delay might reach the maximum of 5.14 ms.
By this measure the average current consumption can be drastically reduced.
Example:
At one ToF measurement in an ultrasonic flow meter (forth/back) per second the highspeed oscillator is active only for about 2 ms.
The average current consumption is 130 µAs * 2 ms = 0.26 µA.
5.1.2
32.768 kHz Oscillator
The TDC-GP21 needs a 32.768 kHz reference for the
start-up control of the high-speed clock and the clock
calibration. It therefore offers an integrated low-power
driver.
The 32.768 kHz oscillator is permanently running and has
a current consumption of only about 0.5 µA at 3.0 V. The
settling time of this oscillator is about 3 s after power -up.
The 32.768 kHz oscillator cannot be switched off. With an
Figure 5.2
external 32 kHz clock from the microprocessor pin
CLK32in has to be connected to GND.
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The low-power clock can be internally forwarded to an output pin to be available for an
external microprocessor. The possible settings are:
32 kHz output at pin FIRE_IN
SEL_TSTO2 = 7:
4 kHz (32 kHz/8) output at pin EN_START
CLK32in
It is also possible to provide an external
low-frequency rectangular clock at the
CLK32Out pin (3.6 V max.).
CLK32out
SEL_TSTO1 = 7:
External
32kHz
Figure 5.3
5.1.3
Calibrating a Ceramic High-speed Oscillator
Using a ceramic oscillator for the 2 to 8 MHz clock will be attractive because it is of low
cost and has a fast settling time. Unfortunately it has a poor tolera nce of 0.3 to 0.5 %
and shows a temperature drift. For this reason the TDC-GP21 allows to execute a
calibration measurement that allows to compensate this behavior. This measurement is
based on the very precise 32.768 kHz clock. The TDC-GP21 generates start/stop pulses
from the 32.768 kHz and measures this time interval with its TDC unit. The result is
stored in the result register and the interrupt flag is set. The frequency error of the
ceramic resonator can be calculated by the microprocessor. The calibration is configured
by setting register 0, ANZ_PER_CALRES and is started with “START_Cal_Resonator“ instruction by the microprocessor.
The time interval to be measured is set by ANZ_PER_CALRES which defines the number of
periods of the 32.768 kHz clock:
ANZ_PER_CALRES
= 0
2 periods =
= 1
4 periods = 122.070 µs
= 2
8 periods = 244.140 µs
= 3
61.035 µs
16 periods = 488.281µs
The results is given in multiples of the high-speed clock and (divided by 1, 2 or 4
(DIV_CLKHS)) as 32 bit fixed point numbers with 16 integer bits and 16 fractional bits.
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The microcontroller can compare this measured value to the the oretical value and
calculate the correction factor for the frequency.
(
)
Example:
The system shall work with a 4 MHz resonator. With DIV_CLKHS = 0 and
ANZ_PER_CALRES = 1 the theoretical result is 122.0703125µs/250ns = 488.28125
(RES_0 = ’h01E84800). If the ceramic resonator in use is not exactly at 4 MHz but only
3.98 MHz the calibration measurement will show 485,83984375
(RES_0 = 1E5D700). The correction factor for the microcontroller is 1.005.
Note: During clock calibration the start input has to be enabled.
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Source Code Example:
//-------------------------------------------------------------------------// Start Calibrate High Speed Clock Cycle
// NOTE: It does not work in combination with EN_AUTOCALC = 1
gp21_wr_config_reg(Bus_Type, 0x83, 0x00000000); // EN_AUTOCALC=0
gp21_send_1byte(Bus_Type, Init);
gp21_send_1byte(Bus_Type, Start_Cal_Resonator);
// Wait for INT Slot_x
Wait_For_Interrupt(Bus_Type);
//Calculate Correction factor (ANZ_PER_CALRES=1)
CLKHS_freq_corr_fact = 122.070/
gp21_read_n_bytes(Bus_Type, 4, 0xB0, 0x00, 16) * CLKHS_freq;
printf("\n Correction factor for clock = %1.3f\n", CLKHS_freq_corr_fact);
CLKHS_freq_cal *= CLKHS_freq_corr_fact; // Calibrated Clock frequency
gp21_wr_config_reg(Bus_Type, 0x83, 0x80000000); // EN_AUTOCALC=1
//--------------------------------------------------------------------------
5.1.4
How to use Clock Calibration
a. Application
This option is dedicated especially to ultrasonic flow and heat meters. In those applications
the use of ceramic oscillators shows two main advantages: lower cost and less current
consumption. Mainly because of the short oscillation start-up time of the ceramic oscillator
the operating current can be reduced by several µA. Referring to 10 years of operation
this saves several 100 mAh in battery capacitance. There is no negative effect on the
resolution when using this option the correct way.
b. Jitter of the 32 kHz clock and consequences
The 32 kHz clock is very precise in frequency with only a few ppm error. However, the
phase jitter is about 3 to 5 ns peak-peak. For this reason also a calibration measurement
(Start_Cal_Resonator) has this error. When multiplying a measurement result with the
calibration result, the jitter of the calibration is transferred to the result by the ratio
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calibration measurement time (see ANZ_PER_CALRES) to measurement time. Using a
permanently updated calibration value will add a considerable jitter to the measurement
result.
c. Application of this option in ultrasonic flow meters
A measurement result is always made of two single time-of-flight measurements in
ultrasonic flow meters, with and against the fl ow direction. The difference between those
measurements is a measure for the flow. To avoid an influence of the calibration jitter on
this measurement result it is necessary only to use the same calibration for both ToF
measurements. Following this, the difference between the two ToF measurements will be
free of the jitter of the clock calibration measurement. The clock can be calibrated only
between measurements that are not directly subtracted from each other.
5.2
Fire Pulse Generator
5.2.1
General Description
The fire pulse generator generates a sequence of pulses which is highly programmable in
frequency, phase and number of pulses. The high-speed oscillator frequency divided by the
factor selected for DIV_CLKHS is used as the basic frequency. This frequency is i nternally
doubled and can freely be divided by a factor of 2 to 15. It is possible to generate 1 to
127 pulses. If maximum 15 pulses are sent the phase for each pulse can be adjusted per
register configuration. The fire pulse generator is activated by sending opcode Start_TOF.
The fire pulse maybe used directly for the START of the TDC.
The fire pulse generator provides 2 outputs, FIRE_UP and FIRE_DOWN. The driver
strength of each output is 96 mA @ 3.3 V. Furthermore, FIRE_DOWN output signal can
be inverted to double the signal amplitude. The outputs can be set individually High-Z.
Alternately, the default level of the inactive buffer can be set to GND.
5.2.2
Configuration
Number of pulses:
ANZ_FIRE
5-4
= 0
Switch off fire pulse generator
= 1
1 pulse
= 2
2 pulses
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…
…
= 127
127 pulses
SEL_START_FIRE
= 1
Fire pulse is used as TDC START
FIRE_DEFAULT
= 0
Default level High-Z (GP2 compatible)
= 1
Default level GND. Mandatory if the internal analog
circuit and the recommended circuit with external R and
C is used.
Phase:
The phase of each pulse can be defined in register 5, PHFIRE[0..14], (Mandatory:
PHFIRE[15] = 0), if not more than 15 pulses are sent. “0“ stands for HIGH-LOW and “1“
for LOW-HIGH. The pulse sequence begins with the LSB and ends with th e MSB.
It is an easy way to halve
Example:
the pulse frequency.
ANZ_FIRE = 15, PHFIRE = ’h0055
For that use PHFIRE =
‘h5555 and defining
straight number of
LSB
[0], [1], …
[14]
MSB
ANZ_FIRE = 14.
Fire pulse frequency:
The input signal fireclk1 for the fire pulse generator is derived from the high speed clock
CLKHS and the selected value for the high speed clock divider DIV_CLKHS.
Pulse-Generator
CLKHS
ffireclk1
1
n
DIV_CLKHS
1
Phaseshift
0.5
ffireclk2
1
m
FIRE_UP
FireGenerator
FIRE_DOWN
DIV_FIRE
frequency
doubling
PHFIRE
DIS_PHASESHIFT
CONF_FIRE
16
3
ANZ_FIRE
4
Figure 5.3
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This Signal is internally doubled and divided by DIV_FIRE.
DIV_FIRE =
0
not permitted
1
divided by 2
2
divided by 3
...
...
15
divided by 16
Register 5, bit 19, DIS_PHASESHIFT actives the phase shift, which introduces additional
noise to improve statistical behavior when averaging.
DIS_PHASESHIFT = 0
Phase shift on
DIS_PHASESHIFT = 1
Phase shift off
fireclk2 is used as reference signal for the FIRE_UP / FIRE_DOWN - signal which is
emitted by the output buffers FIRE_UP / FIRE_DOWN of the fire pulse generator.
Figure 5.4
As shown in Figure 16 at least 2 clock periods T fireclk2 are required to send one fire pulse.
One for the high phase and one for the low phase of the FIRE_UP/FIRE_DOWN output
signal.
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Example:
CLKHS = 4 MHz, DIV_CLKHS = 1, DIV_FIRE = 1
Max. frequency of the FIRE_UP / FIRE_DOWN output signal:
Driver outputs:
The output drivers are configured by setting CONF_FIRE in register 5, bits 29 to 31:
CONF_FIRE configures the FIRE_UP and FIRE_DOWN outputs of the GP21. CONF_FIRE is
used to control which of the outputs (FIRE_UP or FIRE_DOWN) are first fired when the
Start_TOF_Restart command is issued. It is also used to individually enable or disable
these outputs.
Only one of the three bits may be set to 1:
Bit 31 = 1
Fire both outputs (FIRE_UP and FIRE_DOWN) simultaneously. In this
case, the FIRE_DOWN output is an inverted representation of
FIRE_UP.
Bit 30 = 1
Enable FIRE_UP output only, or when Start_TOF_Restart is issued, fire
this output first.
Bit 29 = 1
Enable FIRE_DOWN output only, or when Start_TOF_Restart is issued,
fire this output first.
Note:
In register 5, bits 16 to 18, REPEAT_FIRE originally had been implemented for sing around
measuring. Please set
REPEAT_FIRE = 0
5.3
no repetition
Fast Initialization
In measurement mode 1 the TDC-GP21 offers the possibility of a fast initialization.
Activated by setting register 1, bit 15, EN_FAST_INIT = “1“ the interrupt flag automatically
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initializes the TDC. So the TDC is already prepared for the next measurement while the
data can be read out. This mode is for highest speed applications only. It is most
reasonable for un-calibrated measurements with only one stop.
5.4
Noise Unit
In case the user wants to improve the measuring results by averaging it is necessary that
the values do not always display exactly the same time difference. Instead the user should
provide some “noise” so that different quantization steps of the characteristic curve of the
TDC are involved. This can not happen with very constant time differences. One would
constantly hit the same LSB.
The noise unit enables the use of weighted averaging even for constant time differences.
The noise unit adds a random offset to the start. It is dedicated to applications where the
TDC gets a dummy start and measures the time difference between STOP1 and STOP2
(e.g. laser range finders).
The noise unit is switched on by setting register 5, bit 28, EN_STARTNOISE = “1“
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5.5
EMC Measures
Regarding the EMC susceptibility, there are measures we can recommend:

Most importantly: the housing of the spool-piece must be connected to the
electrical GND signal of the PCB

Using ferrite cores with ~100 Ohm @ 100 MHZ with a low DC resistance, e.g.
MURATA - BLM18EG101TN1D - FERRITE BEAD (Impedance: 100 Ohm, DC
Resistance Max: 0.045 Ohm, DC Current Rating: 2000 mA, Ferrite Case Style:
0603)

Using capacitors (value = 1 nF) between fire outputs and GND

Using a shielded cable

Common mode chokes are not needed
With these measures, we usually see significant improvement.
Please make sure that the capacitors are of C0G type. Use no other types. Values up to
2.2 nF should work without too big disturbance on the measurement result.
EMC protection of transducer (acam-messelectronic gmbh)
Figure 5.4
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6
Applications
6.1
Ultrasonic Heat Meter
The TDC-GP21 is perfectly suited for low-cost ultrasonic heat meter designs. Thanks to the
implemented functionality, including precision temperature measurement, fire pulse
generator, analog switches, comparator, windowing and clock calibration, it is sufficient to
add a simple microprocessor (without A/D converter).
The final circuit reaches a unknown level in compactness and small size. The following
diagram shows the front end section of a typical ultrasonic heat meter as it might look like
when TDC-GP21 is used.
Figure 6.1
The red parts illustrate the external components needed. The number is reduced to a
minimum:

In the ultrasonic path, the piezo transducers are connected through pairs of R and
C.
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
TDC-GP21
In the temperature path only a temperature stable reference resistor and a
capacitor

As oscillators take a 32.768 kHz and a ceramic 4 MHz oscillator. The FIRE_IN pin
can be used as output driver for the 32.768 kHz clock, so the µP does not need a
low power oscillator.

For the power supply use separate bypass capacitors of sufficient size to block V cc
and Vio. Separate both by a small resistor.
In total 11 low-cost elements only are needed for the measurement.
Register
Value
Typical example configuration (*)
Register 0
’ hA30B6800
ANZ_FIRE = 10 (see register 6, too)
DIV_FIRE = 3, fire pulse frequency = 4 MHz/4 = 1.0 MHz
ANZ_PER_CALRES = 0, the 4 MHz is calibrated by a 61.035 µs
measurement
DIV_CLKHS = 0, the 4 MHz ceramic oscillator is internally used as it is
START_CLKHS = 2, the ceramic oscillator has 480 µs to settle
ANZ_PORT = 1, use all 4 ports for the temperature measurement
TCYCLE = 1, 512 µs cycle time for the temperature measurement
ANZ_FAKE = 0, 2 fake measurements
SEL_ECLK_TMP = 1, use 4 MHz for the temperature measurement
cycle definition
CALIBRATE = 1, mandatory in measurement mode 2 to be on
NO_CAL_AUTO = 0, mandatory in measurement mode 2 to have autocalibration
MESSB2 = 1, switch on measurement mode 2 for measuring > 2 µs.
NEG_STOP/NEG_START = 0, all set to rising edges
ID0 = ’h00
Register 1
’ h21444000
HIT2 = 2, HIT1 = 1: calculate 1. Stop - Start in measurement mode 2
EN_FAST_INIT = 0, off
HITIN2 = 0
HITIN1 = 4, measure 3 stops (in measurement mode 2 this includes
the start, too, giving 4 hits)
CURR32K = 0, use default
SEL_START_FIRE = 1, use the internal direct wiring from the fire pulse
buffer to the TDC start
SEL_TSTO2 = 0, EN_START active
SEL_TSTO1 = 0, FIRE_IN pin is used as fire in
ID1 = ’h00
Register 2
’ hA0320000
EN_INT = b0101, interrupt given by Timeout TDC or ALU ready
RFEDGE1 = RFEDGE2 = 0, use only rising edges
DELVAL1 = h’3200, the first stop is accepted after 100 µs
ID2 = ’h00
Register 3
’ h18340000
EN_ERR_VAL = 0, there is enough time to read the status register
SEL_TIMO_MB2 = 3 , time out is generated after 4096 µs
DELVAL2 = h’3300, the first stop is accepted after 104 µs
ID3 = ’h00
Register 4
’ h20360000
DELVAL3 = h’3400, the first stop is accepted after 108 µs
ID4 = ’h00
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Register 5
’ h40000000
CON_FIRE = 2, enable FIRE_UP. If opcode Start_TOF_Restart is used
FIRE_UP and FIRE_DOWN are used alternately for up and down flow
measurements. With the configuration described here the
measurement cycle starts sending fire pulses at pin FIRE_UP.
EN_STARTNOISE = 0, switch off
DIS_PHASESHIFT = 0, phase noise unit is active to improve the
statistical behavior
REPEAT_FIRE = 0, no sing-around
PHFIRE = 0, no phase change in the fire pulse sequence
ID5 = ’h00
Register 6
’ hC0E45000
EN_ANALOG = 1, use the internal analog circuit
NEG_STOP_TEMP = 1, use the internal Schmitt trigger for the
temperature measurement
TW2 = 3, 300 µs delay to charge up the capacitors of the highpass
EN_INT = b0101, interrupt given by Timeout TDC or ALU ready (see
also register 2)
START_CLKHS = 2, the ceramic oscillator has 480 µs to settle (see
also register 0)
CYCLE_TEMP = 0, use factor 1.0 for the Start_Temp_Restart
CYCLE_TOF = 0, use factor 1.0 for the delay between two ToF
measurements
HZ60 = 0, 50 Hz base
FIREO_DEF = 1, mandatory when using the internal analog circuit
QUAD_RES = 0
DOUBLE_RES = 0, use 45 ps BIN
TEMP_PORTDIR = 0, standard order for T measurement
ANZ_FIRE = 10 (see register 0, too)
ID6 = ’h00
(*) the contents of the registers can differ
Measurement flow:
Calibrate Clock:
Power-on reset:
Send SO = ’h03 Start_Cal_Resonator
Send SO = ’h50
Check-loop INTN = 0?
Load configuration from EEPROM to
configuration registers:
Send SO = ’hB0, Read SI = RES_0
Correction factor = 61.035/RES_0
Send SO = ’hF0
Check-loop INTN = 0? for end of EEPROM
action
Measurement loop:
Send SO = ’hB4, Read SI = STAT
Temperature measurement, every 30
seconds:
STAT&’h0600 > 0: -> Error routine
Send SO = ’h06 Start_Temp_Restart
Send SO = ’h81314000 calculate HIT2Start
Check-loop INTN = 0?
Wait for 2.8 μs (ALU time)
Send SO = ’h81414000 calculate HIT3-
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Send SO = ’hB4, Read SI = STAT
Start
STAT&’h1E00 > 0: -> Error routine
Wait for 2.8μs (ALU time)
Send SO = ’hB0, Read SI = RES_0
Send SO = ’hB0, Read SI = RES_0
Send SO = ’hB1, Read SI = RES_1
Send SO = ’hB1, Read SI = RES_1
Send SO = ’hB2, Read SI = RES_2
Send SO = ’hB2, Read SI = RES_2
Send SO = ’hB3, Read SI = RES_3
Send SO = ’h70 Initialize TDC
Rhot/Rref = RES_0/RES_1
Check-loop INTN = 0? (down TOF)
Rcold/Rref = RES_3/RES_2
Send SO = ’hB4, Read SI = STAT
Check-loop INTN = 0?
STAT&’h0600 > 0: -> Error routine
Send SO = ’hB4, Read SI = STAT
Send SO = ’h81314000 calculate HIT2Start
STAT&’h1E00 > 0: -> Error routine
Wait for 2.8μs (ALU time)
Send SO = ’hB0, Read SI = RES_0
Send SO = ’hB1, Read SI = RES_1
Send SO = ’h81414000 calculate HIT3Start
Send SO = ’hB2, Read SI = RES_2
Wait for 2.8μs (ALU time)
Send SO = ’hB3, Read SI = RES_3
Send SO = ’hB0, Read SI = RES_0
Rhot/Rref = RES_0/RES_1
Send SO = ’hB1, Read SI = RES_1
Rcold/Rref = RES_3/RES_2
Send SO = ’hB2, Read SI = RES_2
Calculate the average of the two
measurements.
μP can now start the data post-processing
and
Go to look-up table to get the temperatures
calculate the flow and the heat.
Time-of-flight measurement every half
second:
Send SO = ’h70 Initialize TDC
Send SO = ’h05 Start_TOF_Restart
Check-loop INTN = 0? (up TOF)
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7
Miscellaneous
7.1
Bug Report
7.1.1
FIRE Pulse Generator
A flow measurement has to begin with sending on FIRE_UP. Otherwise, under certain
conditions, noise might be increased. This is avoided easily by starting with FIRE_UP.
7.1.2
TDC-CAL read error without Quad resolution
In case quad resolution is not set then reading separately the TDC cal value will give a
wrong read value. The internal calibration value is correct, but the transfer to the read
register is not correct. Therefore, measurement data are not affected.
Effect in Measurement mode 2:
- In this mode the cal value is for information only. Further, quad resolution is
recommended anyway.
Effect in Measurement mode 1:
- Customers using auto calibration are not affected.
- Only customers that want to read uncalibrated data and do external calibration are
affected.
Workaround:
- The calibration data are not addressed directly after the calibratio n measurement but
after the next regular measurement, before the next INIT.
Example:
Reg1 = ’h21...
Reg1 = ’h67...
result0 = read(adr=0)
cal = read(adr=1)
INIT
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7.1.3
TDC-GP21
Timeout Temperature Measurement
Note: Due to a bug it is necessary to have SEL_TIMO_MB2 at 2ms to get a correct
interrupt indication when 512 µs cycle time is selected.
7.1.4
Timeout TOF Measurement
Problem:
In case there is a timeout (e.g. because of air in the spool piece) the pulse -width
measurement starts but does not end before there is an INIT. Th e current is increased by
500 µA. The problem appears only with active pulse-width measurement.
Solutions:
1.
It is mandatory to answer to any interrupt from TDC-GP21 by minimum an INIT
command. Even in case you know the next data are bad you need to send an INIT to stop
the pulse-width measurement. Also in case you don’t read the data. Of course, timeout
has to be selected as an interrupt source.
7.2
Last Changes
27.05.2010
Target Specification, draft version
28.07.2010
Version 0.1 for release
13.08.2010
Version 0.2 slight changes
08.11.2010
Version 0.3 released
24.11.2010
Version 1.0 relesed, revision of section 4
17.01.2011
Version 1.1 released, several corrections in the whole document
08.02.2011
Version 1.1 small corrections in section 5 and 6.
21.02.2011
Version 1.1 slight corrections in section 3 and 5
03.03.2011
Version 1.2 released. Revision of the measurement flow example in section
6
05.08.2011
Version 1.3,new section 4.3.1 and 7.1. Reg5 corrected and further small
corrections
25.05.2012
Version 1.4 changes on pages 2-5; 3-7; 3-8; 3-10; 4-12; 6-2; 6-3
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14.11.2013
Version 1.5 Correction Status register (EEflags). Smaller additions;
In Measurement Mode 2 Tmin=700ns adapted;
Expands section 2.6 Power Supply, page 2-15;
Description EN_ANALOG (Register 6) adds, page 3-10;
Important supplement to writing the EEPROM, page 3-15;
Description of the configuration of the Fire Pulse Generator adds, page 5 -6;
Add new section 5.5 EMC Measures, page 5-10;
Revised the used registers, page 6-2;
Bug Report completed, section 7.1;
13.03.2014
Version 1.6: EMC section corrected
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Fax
+49 7244 7419 – 29
E-Mail [email protected]
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