The AD7768-4 offers multiplexing a "zero-scale [...] voltage close to 0V". In my understanding this can be used for calibration (by reading the offset of the "shorted" input and applying a corresponding value to the OFFSET REGISTERS). Is this assumption correct?
My problem is that I don't seem to get the multiplexer working correctly. I set all bits in the diagnostic receive select register for the channel and then write the Diagnostic Mux Control register according to the data sheet (0b101). Data is applied correctly, however, there seems to be no effect at all - the adc output data is still not nulled, e.g. I still see the sine input I feed to the inputs.
What am I missing here?
Additionally: By using full scale and full negative scale muxed voltages, could I calibrate the gain?