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Periodically Wakeup from LPM3

Victor44251
Intellectual 310 points

Other Parts Discussed in Thread: MSP430F235

Simple question - is it better from a low power perspective to wake up from LPM3 using the WDT (running in interval mode) to fire a wakeup interrupt or using TIMER_A to generate an periodic wakeup interrupt? Assume both are using being sourced by the VLO. In case anyone is thinking "it depends on the specific MSP430 variant," I am using the MSP430F235.

  • 0
    Guru 12050 points

    You will only have 4 time options with the WDT, the Timer_A can be set to 'any' time.

    Using WDT will let you use Timer_A for something else like pwm.

     

  • 0 in reply to Tony Philipsson
    Intellectual 310 points

    I recognize that the Timer_A is more "flexible" than the WDT for waking up. However, by combining the DIVA prescalar and the WDT prescalar, you can get 16 different wakeup-rates. The meat of my question is really only which approach consumes less power.

  • 0 in reply to Victor44251
    Genius 4170 points

    Victor44251 said:
    The meat of my question is really only which approach consumes less power

     

    Hello,

     

    can you not meassure the current consumption in both modes, since they dont seem that time intensive to implement?

     

    If you do so i would be glad to get those results too, as i am also trying to get the power consumtion as low as possible, i am currently at 3 µA in LPM3.

    This first approach of mine was to simple never periodically exit the LPM3 but instead wake up on a Button-pressed event, but now that i am thinking of it i can only guess

    that not everyone has a user-driven application, so perhaps you really need a periodically wake-up :)

     

    Ok anyway, would be interested in the results.

    Thanks. Seb

  • 0 in reply to Victor44251
    Guru 227245 points

    The unbeloved answer to this question is: it depends.

    Since waking up from LPM requires some dead time in which the MCU isn't working but consumes full power, the question is: how often shall the interrupt happen. Also one question is: how fast do you need to respond to the interrupt? Just switch off MCLK for instant wakeup, or shutting doen DCO and maybe the crystals for occasional, not time-critical wakeups.

    The WDT requires less power, especially if you run it from the VLO. If everything else is really off, and you can live with the few timings available with the WDT, then WDT and VLO is the lowest current. And the least comfortable.
    If your MSP has a VLO at all. (the available options differ with the MSP family and sometimes sub-family)

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