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AD7731 via Arduino SPI

We're using an Arduino to control an AD7731.  We think the SPI interface is working in that we can 1) trigger a reset by writing four 0xFF bytes and see the RESET pin go low via our logic analyzer and 2) After the reset, we read the Mode register and get back 0x174 as per the data sheet.  Our problem is that when we try to do a continuous conversion read operation, fully differential, AIN1(+) and AIN2(-), 0 - 1.28 V, Mode bytes as follows (MSB first)   00110001  01110100, we can't ever get the RDY pin to go low.  Is there a way to check the operation of the chip so see if conversions are being made and put in the data register at all?  I don't think we fried the chip, but we don't have a way to check.  Also, we are using the AD780 2.5V reference.  We could send you code if that would help.



  • Since it's been two weeks without any contact, I'll try one more time before we just fix it ourselves or simply switch to another chip.  We've now tied the /SYNC, /RESET, and /STANDBY chips through 10k resistors to +5V.  We did a full scale internal calibration, then an internal zero calibration.  We confirmed that the gain and offset register values were changed.  We gave 0.63 V to AIN2 with AIN1 tied to ground.  (The calibrations were performed without removing these connections.)  We even buffered that input through an op amp voltage follower in case our voltage divider couldn't provide enough current.  We can't get the chip to give us the correct result.  We know the serial comm is working ok, since we can monitor the command bytes, etc with our logic analyzer and see the correct values.  Any suggestions?

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