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ADS1247: Fail to get conversion data

Dave Stevens
Prodigy 40 points
Part Number: ADS1247


Hi

I'm using an ADS1247 with PIC32MX530. I previously had an issue reading any regs from the device - now resolved; however I can not get any valid conversion data.

The unit is connected to a PT100 identically to the apps note in a 3 wire application. The regs are programmed with the same values as the apps note(see analyser display below which shows the regs read out for verification).

Looking at the pins of the ADS the excitation currents are on a valid voltage is appearing across the REFP and REFN (gnd) and I can measure a voltage across the PT100 but all zeros from theSPI.

The second display shows the reads.

Thanks

Dave

  • 0
    TI__Guru* 98275 points
    Dave,


    Looking at the logic analyzer output, I think the problem is in the FSC2 register. This value scales the output from the digital filter and determines the gain error. Normally this register should have a value somewhere near 40h (with the full FSC value at 400000h), but it looks like you've over-written it to 00h. With this value, I would guess that you're getting 000000h as your output data all the time.

    Generally, you don't want to over-write the FSC value. For the ADS1247, the FSC value is factory trimmed for each gain setting and you'll get good performance with the factory setting, which is imported for each change of gain.

    If the FSC isn't the problem, I would check the reference setting and make sure that the reference used is REF0. I would also measure back the input voltage and the reference voltage with a precision multimeter, and then report back what you get for the output data. It's always good to compare the output data with what you expect.

    Regardless, let me know if the leaving the FSC register alone works (or if you program the FSC2 to 40h). Hopefully, it solves your problem.


    Joseph Wu
  • 0 in reply to Joseph Wu
    TI__Guru* 98275 points
    Dave,


    Out of curiosity, did my comments help solve your problem? I just wanted to make sure you got a solution to your output data error. I'll close this post for now, but if you want to continue to ask questions, you can add on to this post, or contribute a new post if you get locked out.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 40 points

    Hi Joseph

    Yes, many thanks sorry not to have notified you. I've been on a customer's site for a couple of days.

    I would have been a while finding that as the register settings were, initially, taken from an apps note where those regs were marked as XX.

    Butt all working now,

    cheers

    Dave