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ADS1298: Data Format

Phil Wainman
Prodigy 80 points
Part Number: ADS1298

When I decode the data from my ADC, if the data isn't clipping at + or - FS, the decimal data format always seems to be a round number of 10. Is this normal?

-7213910,-8388608,-8388608,-8388608,-8388608,-8388608,-4455520,
-7213970,-8388608,-8388608,-8388608,-8388608,-8388608,-4324200,
-7213810,-8388608,-8388608,-8388608,-8388608,-8388608,-4187900,
-7212920,-8388608,-8388608,-8388608,-8388608,-8388608,-4044030,
-7212630,-8388608,-8388608,-8388608,-8388608,-8388608,-3888240,
-7212340,-8388608,-8388608,-8388608,-8388608,-8388608,-3721980,
-7212160,-8388608,-8388608,-8388608,-8388608,-8388608,-3550390,
-7211390,-8388608,-8388608,-8388608,-8388608,-8388608,-3371610,
-7211130,-8388608,-8388608,-8388608,-8388608,-8388608,-3192150,
-7211360,-8388608,-8388608,-8388608,-8388608,-8388608,-3012240,
-7210300,-8388608,-8388608,-8388608,-8388608,-8388608,-2832810,
-7209390,-8388608,-8388608,-8388608,-8388608,-8388608,-2650840,
-7208570,-8388608,-8388608,-8388608,-8388608,-8388608,-2465140,
-7209130,-8388608,-8388608,-8388608,-8388608,-8388608,-2269890,
-7208890,-8388608,-8388608,-8388608,-8388608,-8388608,-2060830,

  • 0
    TI__Guru 66176 points

    Hello Phil,

    Thank you for your post.

    Could you share the raw ADC data in hex format that correspond to those channels? 

    Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 80 points

    Not that capture but have these:

    Packet Start Time (s) End Time (s) Data
    1 5.76E-07 5.50E-05 C0 00 00 04 A4 52 91 6C 9E 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 04A452 304210
    2 0.000125568 0.00018 C0 00 00 04 A3 6C 91 6E 92 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 04A36C 303980
    3 0.00025056 0.000304992 C0 00 00 04 A5 88 91 6D 84 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 04A588 304520
    4 0.000375552 0.000429984 C0 00 00 04 AB 8C 91 6D 98 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 04AB8C 306060
    5 0.00050064 0.000554976 C0 00 00 04 B2 62 91 6E 42 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 04B262 307810
    6 0.000625632 0.000679968 C0 00 00 04 B1 D6 91 6B B8 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 04B1D6 307670
    7 0.000750624 0.00080496 C0 00 00 04 B5 8C 91 6E BA 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 80 00 00 04B58C 308620
    8 0.000875616 0.000900288 C0 00 00 04 B2 62 91 6D 02 80 00 00 4 04B262

    307810

  • 0 in reply to Phil Wainman
    TI__Guru 66176 points

    Hi Phil, 

    I'm still not sure about this one. The last few LSBs should always toggle due to the intrinsic noise of the converter. Could you show a logic analyzer capture zommed in on the first 48 bits of one frame (just STATUS word + CH1 data) with /CS, SCLK, DOUT, /DRDY? I'll take a look at the timing of the SPI signals. Please provide the SCLK frequency and confirm that you are using CPOL = 0 and CPHA = 1.

    Another question - is this only observed on Channel 1? Or have you seen this behavior (multiples of 10 only) on other channels?

    Please also provide a list of the register settings used for the test.

    Best regards,

  • 0 in reply to Ryan Andrews
    Prodigy 80 points

    It isn't the fact that they are the last few bits - because it is a rounding to decimal. Trace captured above. Odd behaviour is with all the channels.

    Register setup.  Config1 0x82, (High resolution 8KSPS) Config2 0x02 (test signal not used), Config3 0xC0 (Internal reference 2.4V)

    Channel configs 0x21 for noise test otherwise 0x10.

  • 0 in reply to Phil Wainman
    TI__Guru 66176 points

    Post has been taken offline.