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ADS131A02: ADC responds to NULL Command with SPI fault after enabling the channels

Katja Ehlen
Prodigy 20 points
Part Number: ADS131A02

We are controlling the ADS131A02 with SPI communication in asynchronous slave mode and 32 bit device word length without hamming code. The steps for initialization are executed according to the data sheet and it seems to work properly. However, as soon as we enable the adc channels, the response of the NULL command changes from 2200h to 2220h indicating an SPI fault. The F_FRAME bit in the STAT_S register is also set, so the number of clock cycles per frame seems to be too low. We observed the cycles and the dataframes with the oscilloscope and we could not detect any problems there. The error disappears after disabling the channels. Is there an explanation for this behaviour? The data conversion seems to work correctly despite the error message.

  • 0
    TI__Guru* 97755 points

    Katja,



    As you mention, the F_FRAME error that you get comes from the device not getting as many SCLKs as it expects. My first guess would be that once the ADCs are enabled, the device is expecting to clock out the ADC data for all the channels of the device. Because of this, the device is expecting the extra 48 SCLKs for data and 16 for CRC.

    Note that the F_FRAME error should clear with a read of the STAT_S register as long as the error doesn't continue to happen. With the ADS131A02, you can test this by adding in the additional SCLKs for each transaction after the enabling of the ADC that didn't originally have a read data associated with it. The device shouldn't flag extra SCLKs as an SPI error.

    If you continue to have problems with this error, post the transaction giving the error and the following status response showing the error. We should be able to work out a solution.

     
    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 20 points

    Thank you very much. We increased the number of clock cycles per frame after enabling the channels and it worked. The SPI error does not appear anymore.