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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.

Thanks,

George

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  • Hi George,

    Don't see any problem with your code. Can you send me a schematic diagram. How are you driving pin 2 the MCLK IN? And how is the filter register programmed?

    One thing to try. Once the part is programmed to operate in continuous conversion mode, stop the code there and check the RDY pin with an oscilloscope, it should be toggling at the filter register programmed output data rate.

    Regards,  Brendan.


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  • Hi George,

    Don't see any problem with your code. Can you send me a schematic diagram. How are you driving pin 2 the MCLK IN? And how is the filter register programmed?

    One thing to try. Once the part is programmed to operate in continuous conversion mode, stop the code there and check the RDY pin with an oscilloscope, it should be toggling at the filter register programmed output data rate.

    Regards,  Brendan.


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