AD7124-4: Read command does not response unless CS is constant low from GND in EVAL-AD7124-SDZ

Hello,

We are trying to read the ID register with CS controlled via SPI module or GPIO (both mechanism) has being used (we used the sample code and SW reset routine is called in init routine as well). But, there is no response from the slave.

We are getting the response for the same command with CS line as constant low using GND from in EVAL-AD7124-SDZ. Also, there is no response from slave if it is connected to GND from micro controller board.

Delay between the clock falling edge to start of clock is set from 3us (using SPI) till 70us (using GPIO)  and still there is no response for command.

Please let us know what could be the reason for this behaviour.

Even with chip select kept at constant low and loop over all registers and compare it default values after reset, we are getting approx. 10 times success against 400 times failure for all register read. Please let us know what could be the reason for this behaviour as well.

Note: In the waveform.png that attached, it is the same behaviour when we tested with CS low during entire SPI total command.

Note: Master is TMS570LS1224 from Texas Instrument.



Note added for waveform picture
[edited by: ArshadZiyad at 4:35 PM (GMT 0) on 14 Nov 2019]