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ADS1255: SDATAC command after reset

Martin Velek
Prodigy 80 points
Part Number: ADS1255

Hello,

I have checked many threads related to read data continuous mode and sometimes there is mentioned: "Also, after RESET, the device will default to RDATAC mode", see https://e2e.ti.com/support/data-converters/f/73/p/889689/3292609. 

Can someone point me out to the ADS1255 datasheet where there is specified that the data continuous mode is the default one? I do reset via RESET/ pin and this information would be very important. What I have observed so far, the WREG command + register data is ignored right after reset and there must be ~600 us delay (it does not depend if DRDY/ is high/low) between RESET/ goes high and first WREG command.

BR

Martin

  • 0
    TI__Mastermind 34981 points

    Hi Martin,

    Let me look into this question and get back to you soon. Hopefully by tomorrow (Friday), but by Monday at the latest

    -Bryan

  • 0 in reply to Bryan Lizon86
    TI__Mastermind 34981 points

    Hi Martin,

    We have determined in the past that after power-up the device defaults to SDATAC mode, so it would make sense that this also occurrs after RESET. I will look into identifying a definitive answer for you, but that will take some time and I wanted to get you some information by today. We would also recommend sending the SDATAC command after toggling RESET to be absolutely sure the device is in this mode.

    For the second question regarding the time from RESET = high to DRDY = low: the datasheet explains this timing, albeit in pieces and in several different places. You must wait until DRDY goes low to issue the next command after after issuing RESET (whether by command or by toggling the pin) (pg. 6, first image below). When RESET occurs, the device registers restore to their defaults (pg. 27, second image). This sets the device to PGA = 1, data rate = 30 kSPS, and then performs a self calibration (pg. 27, second image). The self-calibration at these gain and data rate settings takes ~ 600us, per Table 21 (pg. 25, third image), at which point DRDY should assert low. Since I assume you are measuring from RESET = high to DRDY = low, this matches what you are seeing.

    Let me know if this makes sense.

    -Bryan

  • 0 in reply to Bryan Lizon86
    TI__Mastermind 34981 points

    Hi Martin,

    I have confirmed with one of our digital designers that  that the default mode after RESET is SDATAC. It would still be best practice to send the SDATAC command after toggling RESET to be absolutely sure the device is in this mode however.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 80 points

    Hi Bryan,

    thank you, it makes sense. I was more curious if there is a possibility to terminate the self-calibration process after start-up caused by the RESET/ pin.

  • 0 in reply to Martin Velek
    TI__Mastermind 34981 points

    Hi Martin,

    Thank you for clarifying your question.

    There is unfortunately no way to bypass this RESET functionality on the ADS1255.

    -Bryan