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ADS1296 twice RDATA commands

MichRFT
Expert 2110 points
Other Parts Discussed in Thread: ADS1296

Hello,

I have the following configuration for the ADS1296

The START pin is low

The SINGLE_SHOT bit of CONFIG4 register is set to 1

A SDATAC command has been performed

I send a RDATA command and I read some values from the CHn channels.

I send a 2nd RDATA command and I read some different values from the CHn channels. (a few different)

=> why is there different values between these 2 reads while the START pin is always low?

=> if the RDATA trigs an acquisition, why is there not nDRDY signal change?

=> can I trust these values received


Best regards

Michel Le Mer

  • 0
    TI__Mastermind 38745 points
    Hey Michel,

    SINGLE_SHOT mode is a rarely used mode for situations that require a truly unconventional data rate. Does your application require this, or could you instead simply collect data in continuous mode in one of the data rates which come standard with the device?

    If you do need an unconventional data rate, you should know that in single shot mode, the START command will reset the digital filter thus requiring that the device wait 4 conversion cycles before outputting data. You will need to wait for DRDY for the data to be trusted. RDATA does not trigger conversions, it just tells the device to shift existing data out on the MISO line.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Expert 2110 points

    Brian Pisani said:
    Hey Michel,
    RDATA does not trigger conversions, it just tells the device to shift existing data out on the MISO line.

    => this is my question : why do I read 2 different values for 2 consecutive RDATA commands without a START command?

    these values are just a few different

    Mich

  • 0 in reply to MichRFT
    TI__Mastermind 38745 points
    Hey Mich,

    At that point in time the internal state machine is in some unknown state. I'm not sure what to expect there, but it's definitely not reliable data.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Expert 2110 points

    Hi,

    Do you mean that after a START I can not do many RDATA commands?

    In the datasheet, what is the interrest of:

    When reading data with the RDATA command, the read operation can overlap the occurrence of the next DRDY without data corruption.

    Best regards

    Mich

  • 0 in reply to MichRFT
    TI__Mastermind 38745 points
    Hey Mich,

    You should wait until a DRDY signal to retrieve data. That statement simply means that if you are still collecting data from the previous conversion cycle using the RDATA command when the subsequent DRDY signal occurs, the current acquisition will not be corrupted with new data. This is in contrast to continuous collection where if your collection runs past the next DRDY signal, new conversion data will be loaded into the output shift register while you are collecting and the current acquisition will contain invalid data.

    Does a requirement of your application prevent you from collecting data continuously?

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Expert 2110 points

    Hi Brian,

    Ok, I fully respect your advices concerning the scheduling.

    The goal was a test of the ADS1296. But I am still confused with some read values so I open a different post to avoid topics mixing.

    Best regards

    Michel