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MY ADS1248 not sending data

rakesh joshi
Prodigy 70 points
Other Parts Discussed in Thread: ADS1248

Hi All

I am trying to use ADS1248 as general purpose ADC.  I am using internal clock and reference 

I have written all the registers accordingly and I am able to read those registers (SPI is working). My internal reference is turned on  I can measure the voltage across the VREFOUT and VREFCOM which is 2.04 V.

When I try to read the data (AIN0-AIN1) all I get is zeros. I am attaching screen shot of saleae with this submission

Channel 4 is DRDY and Channel 5 is start. 

  • 0
    TI__Guru* 92715 points
    Rakesh,


    I wrote a blog on debugging digital communications earlier in the month. Read through it and see if it helps.

    e2e.ti.com/.../help-i-can-t-talk-to-my-data-converter-what-s-wrong

    To help debug this I'd make sure the device is really converting. First I'd check to see if the there is anything coming out of /DRDY. This will show if the device is making conversions. However, I think this is probably going to be ok. It looks like Channel 4 rises on the first SCLK and that's what I would have expected. That probably means that the digital section is alive and is responding to SPI communications.

    What are you measuring for the input? Is it close to 0?

    Have you changed any registers? If you have, what have you changed them to? Regardless of the setting, try reading back all of the registers to make sure they are what you expect them to be.

    Right now, I'm not sure what the problem is, but I would suspect one of two things. The first is that you have a bad connection to DOUT. You can verify the connection by being able to read back the registers. The second would be a bad value in the FSC register. If you've accidentally set the FSC register to 000000h, you might get this problem. Generally this value would be close to 400000h and it's use is shown in the datasheet on page 31 in the calibration section. Just look at Figure 66.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 70 points
    Hi Joseph,

    I am able to write registers and read them (I can see exact same values I wrote). You are right It was FSC register I wrote zero on it.

    Thanks a lot
  • 0 in reply to rakesh joshi
    TI__Guru* 92715 points
    Rakesh,


    I'm glad you found the problem.

    I did want to point out that these devices are factory trimmed to get a very good gain error. If you change the PGA gain or the data output rate, the ADS1248 will automatically update FSC to a value that should have a low gain error that is programmed from the factory. Ideally you shouldn't have to update this value yourself.

    If you have any other questions, you can post again on this forum.


    Joseph Wu