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MSP430F67621A: automatically change to RTC mode in power out

Lawrence M
Prodigy 100 points
Part Number: MSP430F67621A

Dear TI community,

I am looking at a design using a MSP430F67621A, it has a coin cell battery backup on AUXVCC3 and has an external crystal for X1.

The RTC works in normal operation. What I notice is that during power out (on DVCC and AVCC) the RTC date/time registers retain their value at power out time but do not continue ticking.

I can see I the in mode LPM3.5 that “RTC clocked by low-frequency oscillator” and I can confirm that if I put the uC into LPM3.5 then kill the primary power the RTC continues ticking and time is maintained during power-out.

What I would like to achieve is a way of being able to cut the primary power (DVCC and AVCC) and the RTC to continue ticking automatically. So I have 2 questions:

1: is it specifically being in LPM3.5 which is required to keep the RTC ticking during primary power-out.

2: is there a way to automatically get into the state where the RTC is ticking during primary power out? I can’t be in a LPM during normal operation.

Thanks.

  • 0
    TI__Genius 10860 points

    Hi Lawrence,

    my first suggestion would be to check out this related E2E post to see if this can also solve your issue:

    1) Could you please check if the capacitance connected to Vcc is in the right capacitor range?

    2) Please also note the following section in the User's Guide:

    Please let me know after checking those two items.

    Thanks and best regards,

    Britta

  • 0
    TI__Genius 10860 points
    Hi,

    as I didn't hear back from you in a while I assume that your issue has been solved.
    Please go ahead and verify the given answer to also help other users that might run into the same issue.

    Note that I'll go ahead and close this thread in the next couple of days if I don't hear back from you. Replying to the thread will re-open it if necessary at some point.

    Best regards,
    Britta
  • 0 in reply to Britta Ruelander
    Prodigy 100 points

    Hi,

    The links you sent over were very useful thank you.

    I have now got my board running the RTC in power off as desired. I effectively rewrite the function using the TI API rather than register bashing and it just started working. I am not sure exactly what fixed it but it is fixed.

    Thanks.

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