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AD7779 SPI readback difficulties

Question asked by Ivan-Rusov Employee on Jul 30, 2018
Latest reply on Aug 9, 2018 by Ivan-Rusov

Hi,

 

AD7779 evaluation board (EVAL-AD7779FMCZ) is used. SPI Control Mode is used for configuration of AD7779 and for reading back sigma-delta conversion data.

The only one SPI port of MCU available for ADC configuration and reading the conversion data (DOUTx pins are not used).

no-OS drivers from ADI website is used.

After AD7779 initialization procedure there is an ability to readback the data from sigma-delta ADCs (via DCLKx pins).

 

I have 2 issues with the AD7779.

  1. When I try to program Offset and Gain Correction (by modifying CHx_GAIN and CHx_OFFSET registers) I see that only CHx_OFFSET impact on ADC conversion data.
  2. When I reprogram PGA Gain (CHx_CONFIG) there are no influences on ADC readback data.

 

How could the issues be solved? There are no clear explanation in the datasheet how to use AD7779 SPI (DCLKx pins) for configuration (calibration, PGA gain change) and reading back the conversion data simultaneously.

 

If you need any specific information please let me know.

 

Regards,

Ivan

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