VCM-DAS-3 datasheet(38/42 Pages) ETC2

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Calibration

VCM-DAS-3 Reference Manual

Calibration

Calibration, if desired, is accomplished by mathematical transformation in software. Gain for the

board (not individual channels) can be adjusted using the ENCTRL register. Offset adjustments

are not currently implemented on the board.

An SPI transaction to the gain pot will take less than 10 us. However, the Gain pot takes up to 20

ms to update its EEPROM when written to. During calibration, you need to wait 2 ms after the

write command before measuring the voltage of the DAC output.

SETTING THE GAIN

The range of gain adjustment is 24 mV. The gain is encoded using the eight bits of the

ENDATLO register, so each step equals 0.094 mV. To perform the Set Gain command, write E0h

to the ENCTRL register at I/O port 0x30A, and then write the gain value to the ENDATLO

1. Select channel 0 by writing 0h to the DACSEL register at I/O port 0x302.

2. Output the code for 0V by writing 0h to both the DACHI and DACLO registers.

3. Using high-precision volt meter (VOM), read the voltage on channel 0. The voltage read

is the offset.

4. Output the code for known voltage minus the offset to channel 0.

5. Using the VOM, read voltage on channel 0. The difference between the VOM reading

and the known voltage applied in step 4 is the gain error.

6. Adjust gain pot up or down to reduce the gain error to the lowest possible amount.

Note that there is no adjustment for offset error. You must accommodate for offset with software.

The gain value you set is non-volatile.

READING THE GAIN

To perform the Read Gain operation, write F0h to the ENCTRL register at I/O port 0x30A, and

then read the value of the ENDATLO register at I/O port 0x308.

VCM-DAS-3 Datasheet(PDF) 38 Page - List of Unclassifed Manufacturers