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ADS131E08: Status word [GPIO byte] format?

Bruce McKenney
Guru 103215 points

Part Number: ADS131E08

Per Data Sheet (SBAS561C) Fig 37, the third byte of the status word contains GPIO[7:4] (presumably referring to the GPIO register (20)). This uses 4 bits to define an 8-bit byte, so I want to make sure what it means.

Observed behavior is that GPIO[7:4] appears as bits [3:0] (low nybble) in that status word byte. The high-order nybble seems to always read as 0xF0 (but maybe I'm not watching closely enough).

My notion is to put a "well known" bit pattern into the GPIO register and use the status word to detect whether the ADC has been Reset. I'll be using a fairly heavy hammer if that happens (presumed rare), so I want to get it right.

Is it correct that GPIO[7:4] appears as bits [3:0] in the third status word byte? Is there any useful information in bits [7:4] of the third status word byte?

  • +1
    TI__Guru 59521 points

    Hi Bruce McKenney,

    The STATUS word is shown below, where the first four bits are always 0xC, followed by 8 bits of STATP, 8 bits of STATN, and then 4 bits of GPIO. So yes, there is useful information in those first 4 bits in the last byte in the STATUS word. Also that info is read only, so you cannot control what it is unless you force the corresponding inputs beyond the threshold value you set in the FAULT register

    I think what you want to do with the GPIO bits is possible, you will just need to make sure to set them appropriately depending on what pattern you want to detect, as shown in Table 20

    -Bryan

  • 0 in reply to Bryan Lizon86
    Guru 103215 points

    When I set the GPIO register to (e.g.) 0x50 (all output, with GPIO3/GPIO1 high) the third status byte (MSb first) reads as 0xF5. Similarly for other settings. So far I've only seen 0xF_ in the high 4 bits.

    (I expect it doesn't matter, but I'm using the EVM, so the 10k pulldowns are installed on the GPIOn pins.) The data words are all reasonable.

    Am I mis-reading something?

  • 0 in reply to Bruce McKenney
    Guru 103215 points

    Never mind, I missed the 0xC_ prefix, so everything is shifted down by 4 bits.

    Thanks!

    [Edit: Emphasis added.]