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ADS131M08: SPI reads are inconsistent

Clark Dunson
Prodigy 40 points
Part Number: ADS131M08

Tool/software:

Reading register 0x00 gives the correct values sometimes, and sometimes not. Attached are two screen shots (which don't give much detail yet). Other reads also seem OK about half the time. Seems our timing may be weak. This app is built on hal.h and ads131m0x.h (slightly changed) and runs on a Raspberry Pi 4. I can supply source code as needed.

I know these high level traces are not very useful, they're just a start. My Salae Logic Analyzer also produces *.sal files if those are useful. Thank you!

Clark

  • 0
    TI__Mastermind 45805 points

    Hi Clark,

    Can you show a clear timing just for reading register 0x00? two frames are good enough, a RREG command in the first frame and the data in the second frame. You can also upload your .sal file. Your /DRDY signal is weird, are you using fly wires to connect Raspberry Pi to an ADC circuit board? It will be good if you can show the details about your hardware setup and connections, a photo of your setup is helpful.

    BR,

    Dale

  • 0 in reply to Dale Li
    Prodigy 40 points

    Thank you Dale;

    Yes, looking at the DRDY analog trace, (see DRDYAnalogTrace.png) it is barely a blip.

    Tried on capturing the two frames:

    Not sure if I got it right. And yes, the test setup is as you described. The intermediate proto board is used to feed the Salae.

    sal file is attached. (not sure, dialog upload box acted weird, and I don't see it, 768kB)

  • 0 in reply to Clark Dunson
    TI__Mastermind 45805 points

    Hi Clark,

    The signals in your setup are really bad. For example, the SCLK signal  is sweeping at ~1.5V DC, so the SCLK signals may not be recognized by the ADC as a clock. Using fly wires in your setup caused the problems.

    Also, the word length should be 24-bit not 16-bit for each word. Below is a good timing to read the Gain register (04h address) with RREG command and the response 0x0E0E register data is shown in next frame:

    -Dale

  • 0 in reply to Dale Li
    Prodigy 40 points

    Thank you Dale; I will stand down them. We expect the new PCBAs next week, so will pick it up then.

    Clark

  • 0 in reply to Clark Dunson
    TI__Mastermind 45805 points

    Hi Clark,

    Sounds good. I can help you to review your design if you would share them in the private message or you can check TI's design as a reference that is shown in the user guide of ADS131M08EVM. 

    BR,

    Dale