I am working on a project involving reading sensor data using an AD7616 in Software Serial mode. There are 3 problems that I have encountered: There is never any value returned in response to a read register command, the ADC appears to not change register contents in response to a write register command, the values that are returned from a conversion are inconsistent for a consistent input voltage. We have verified the electrical configuration of our PCB for Software Serial mode, that is HW_RNGSEL = 00, SER/PAR = 1, SER1W = 1. We use the internal reference with REFSEL = 1. The undriven analog input pins hover at around 2V. When the pins are driven and a conversion is done (asserting CONVST and waiting for BUSY) the result does correspond to the input voltage, but the slope of the output is very inconsistent, going from around 1000 counts for a 1V increase to less than 500 counts for the same increase. When I try to write to the channel register to change which channel is being selected it has no effect. When I read any register the result is always 0. The setup algorithm is to first reset the ADC, do a dummy conversion, then right to the range registers to the change to +- 5V (which seems to have no effect). Then read conversion results from all channels, by writing to the channel register followed by a CONVST. Please let me know any potential issues with either the setup or the algorithm that could be causing these issues.
