TDC-GP21 datasheet(43/91 Pages) AMSCO

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Ultrasonic-Flow-Converter

TDC-GP21

3-18

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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)

HZ60 = 1(60Hz)

20 ms 16.67 ms

1.5

30 ms 25.00 ms

40 ms 33.33 ms

2.5

50 ms 41.67 ms



’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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