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Original question:

[FAQ] ADS1258 / ADS1158: What is the output data format and LSB size?

ADS1258: Incorrect readings

Michael T Schneider
Expert 3790 points
Other Parts Discussed in Thread: ADS1258

Team, would you be able to help debug the below?

Reference system. We have AVDD @ 5V, AVSS @ ground, AINCOM @ 2.5V, Vrefp @ 2.5V and Vrefn @ ground.
We are reading voltages in pulse convert mode sequentially from 0 to 15 (single ended)

Three things are confusing me.

  1. Readings are not linear throughout the range
  2. Readbacks are flipped (ie 0V in reads highest positive number 0x7FFFFF)
  3. I was not able to read the ID register correct when the Start pin was held high. I would read back 0xFC not the expected 0x8B. 

Configuration registers:

_ads1258_reg.CONFIG0    = 0x1A;

_ads1258_reg.CONFIG1    = 0xF0;

_ads1258_reg.MUXSCH     = 0x00;

_ads1258_reg.MUXDIF     = 0x00;

_ads1258_reg.MUXSG0     = 0x03;  //Channel 0 and 1 Selected

_ads1258_reg.MUXSG1     = 0x00;

_ads1258_reg.SYSRED     = 0x00;

Anything you see that is incorrect? Have you seen this error before?

  • 0
    TI__Mastermind 44680 points
    Hi Michael,

    Would it be possible to see a schematic of the circuit?
    The only thing I can see from the register settings is that you are relying on the external ADC inputs, so it is possible the issue is related to the external amplifier circuit. NOTE: Sometimes BYPAS is mistakenly set high. The naming of this bit would make you think that high bypasses the external amp inputs, but its just the opposite.