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MSP430FR2676: RTC count/configuration after reset?

Jeremy Rodencal
Prodigy 30 points

Part Number: MSP430FR2676

If the RST pin is used to wake the MSP from LPM3.5, is the RTC configuration and count retained?  The MSP is keeping track of the current time, so losing the RTCCNT value means our time will not be accurate anymore.

A quick desktop experiment showed that the count and configuration were retained, but I wanted to confirm that is reliable behavior before continuing with this solution.

  • 0
    TI__Mastermind 47045 points

    Hi Jeremy,

    Yes, RTC is retained in LPM3.5.  Section 6.10.11 in the datasheet shows this and also discusses the different clock sources available.

  • 0 in reply to Eddie LaCost
    Prodigy 30 points

    Thanks for the reply!

    I'm clocking the RTC with the XT1, and waking every half hour to increment an elapsed time counter in FRAM. This is working fine.

    My concern isn't about the RTC running in LPM3.5, it's about the state of the RTC registers after using the reset pin to wake the MSP from that state. Currently I'm using a gpio pin to wake from LPM3.5 when the MSP is off of battery power, but I want to use the reset pin instead. If asserting the reset pin could clear the RTCCNT, my FRAM time counter could miss up to a half hour of ticks.

    The reason for the concern is that in chapter 1.2.1 of the user guide, it states: `Other peripheral modules and registers are initialized as described in their respective chapters in this manual.`

    Looking at the RTC section (15) of the guide I couldn't find anything about the register states after a reset.

  • 0 in reply to Jeremy Rodencal
    TI__Mastermind 47045 points

    Jeremy,

    I apologize.  I missed an important part of your question.  The answer is that, yes, after a reset, the count will be cleared.  In the users guide, figure 15-6, the values shown in brackets are the values of this register after a reset.  As you can see, they are cleared to 0 after reset.  

    If you want to wake up from interrupt, I recommend using a GPIO pin instead to wake.  

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