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ADS1248: Using SYNC vs WAKE to initiate a conversion

Robert Poor1
Prodigy 180 points
Part Number: ADS1248

In our configuration:

  • START line is held high
  • Using SPI commands (SYNC, SLEEP, WAKEUP) rather than IO lines for control.
  • SDATAC command has been given to disable continuous conversions
  • Using DRDY- interrupts to signal conversion complete

As per section 10.1.7, a SYNC command will initiate conversions.  When I'm finished doing some conversions, I issue a SLEEP command to save power.

When I'm ready to do more conversions, do I need to issue a WAKEUP command, or will another SYNC command do the same thing?

What happens if the system is awake and I issue a WAKEUP rather than a SYNC?

In other words, what are the key differences between WAKEUP and SYNC commands?  In what way are they (and are they not) interchangeable?

  • 0
    TI__Mastermind 38771 points

    Hi Robert Poor1,

    Here are the answers to your questions:

    Robert Poor1 said:
    When I'm ready to do more conversions, do I need to issue a WAKEUP command, or will another SYNC command do the same thing?

    If you have used the SLEEP command to put the ADS1248 into powerdown mode, you should always issues the WAKEUP command to wake up the ADC. The SYNC command will not work in powerdown mode (see the footnote for Table 19)

    Robert Poor1 said:
    What happens if the system is awake and I issue a WAKEUP rather than a SYNC?

    Why would you do this? In this circumstance the WAKEUP command is effectively treated like a NOP

    Robert Poor1 said:
    In other words, what are the key differences between WAKEUP and SYNC commands?  In what way are they (and are they not) interchangeable?

    The WAKEUP command brings the ADC out of powerdown mode and starts a new conversion, the SYNC command only starts a new conversion

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 180 points

    "Why would you issue a WAKEUP rather than a SYNC?"

    If WAKEUP always starts a conversion, then I don't need the extra logic to track if the ADC is in powerdown or not.  (And if that's the case, I don't see why you'd ever need the SYNC command.)

    But if I interpret your reply correctly:

    • If the system is in powerdown mode, a WAKEUP command brings the system out of powerdown mode and starts a new conversion.
    • If the system is NOT in power down mode, a WAKEUP command has no effect.

    ... that means that before I start a new conversion, I should check if the system was previously put into power down mode (and thus do a WAKEUP) or not (and thus do a SYNC).

    It that about right?

  • +1 in reply to Robert Poor1
    TI__Mastermind 38771 points

    Hi Robert Poor1,

    Robert Poor1 said:
    • If the system is in powerdown mode, a WAKEUP command brings the system out of powerdown mode and starts a new conversion.
    • If the system is NOT in power down mode, a WAKEUP command has no effect.

    ... that means that before I start a new conversion, I should check if the system was previously put into power down mode (and thus do a WAKEUP) or not (and thus do a SYNC).

    Yes this is correct

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 180 points

    Thanks.  (Standby for a related question about the documentation!)  :)

  • 0 in reply to Robert Poor1
    TI__Mastermind 38771 points

    Hi Robert Poor1

    Glad we could resolve this issue quickly

    -Bryan