TDC-GP21 datasheet(49/91 Pages) AMSCO

49 / 91 page

Ultrasonic-Flow-Converter

TDC-GP21

4-4

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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_AUTO = “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

6 = Cal1 Ch1

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 raw data to the

output register).

(

)

Examples:

Reg1 = ‘h01xxxx - 1st Stop Ch1-Start

Reg1 = ‘h2Bxxxx - 3rd Stop Ch2-2nd Stop Ch1

Reg1 = ‘h06xxxx - Cal1

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