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AD7682 / AD7689 - CFG not updating

Question asked by Janusz90 on May 1, 2013
Latest reply on Jul 13, 2016 by tbaruah

Hello,

 

I am trying to communicate with AD7689 via SPI interface but it seems that I am unable to update the configuration register. By looking at the ADCs readings I can see that after updating CFG device is always set to biopolar differential pairs, IN0 and IN1, internal reference = 2.5V, sequencer disabled (most of the bits are 0s?).

 

I want to operate in read/write after conversion (RAC) without busy indicator mode.

 

My code is as follows:

 

CNV-high

delay(800us)

CNV-low

SPI send - 0x3DC1;  (CFG= Unipolar referenced to GND, IN3, full BW, Internal ref=2.5V, disable sequencer, do not read back configuration)

CNV-high

delay(800us)

CNV-low

SPI send - 0x0000;

CNV-high

delay(800us)

CNV-low

SPI send - 0x0000;

........

 

From my scope i can see that Tcyc = 1.4ms. (Period of CNV line)

CKL=28kHz

 

Green - CNV

Pink - SDO

Blue - SDI

Yellow - CLK

 

SPI signals when updating CFG.

CFG.JPG

 

 

SPI signals when 0x0000 is send.

Sample.JPG

 

Please let me know what could be the problem.

 

Thanks.

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