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RTC timer - waking from LPM4

Daniel Berenguer
Expert 2185 points
Other Parts Discussed in Thread: CC430F5137

According tp the CC430 datasheet, LPM4 does not support waking up on RTC timer events. However, my CC430F5137 boards are able to do so. Is this another "elastic" constraint that has to be taken more as a serious recommendation than as a real limitation?

Thanks for your comments.

  • 0
    Guru 227245 points

    The CC5137 has an RTC_A, on which you can select the clock to use (ACLK or SMCLK).
    If the timer is active, the selected clock is requested. Which keeps ACLK or SMCLK active even if you try to enter LPM3 or LPM4.

    So the statement is correct but misleading: If you really enter LPM4, it means that the RTC doesn't have a clock and therefore no RTC events can occur. However, if RTC events occur, you did not really enter LPM3/4. LPM4 and RTC operation (whetehr calendar or timer mode) are mutually exclusive.
    Keep in mind that the debugger usually prevents LPM >0.

  • 0 in reply to Jens-Michael Gross
    Expert 2185 points

    Jens-Michael Gross said:
    Keep in mind that the debugger usually prevents LPM >0.

    OK, this has to be the case since I was doing my tests with the ez430 connected to the target board.

    Thanks a lot Jens Michael for the clear response.

  • 0 in reply to Daniel Berenguer
    Expert 2185 points

    I did some additional tests, this time without the debugger connected to the target board and the CC430F5137 is definitely able to wake up on RTC timer events after entering LPM4. Well, even if I  programmed the application to enter LPM4 I'm not sure it did so since the current consumed is exactly the same as when it enters LPM3 (~1.2 uA).

  • 0 in reply to Daniel Berenguer
    Guru 227245 points

    Daniel Berenguer said:
    Well, even if I  programmed the application to enter LPM4 I'm not sure it did so since the current consumed is exactly the same as when it enters LPM3 (~1.2 uA).


    Apparently, the active RTC keeps ACLK (or SMCLK) active, so you don't really enter LPM4.
    Well, LPM4 says 'ACLK off' while RTC active mean 'ACLK on'. You can't have both. And apparently the RTC wins.
    The users guide doesn't tell whether RTC_A issues a conditional or unconditional clock request. However, the default is to honor conditional requests anyway.

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