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5xx and Real Time Clock

Steven Crawford
Prodigy 110 points

Hi,

 

A quick question, it may seem silly, but... after reading the RTC section of the user's guide, I had one completely unanswered question. 

 

Is the RTC persistent through reset?  Does it guarantee to maintain accuracy through reset?

 

Thanks in advance,

 

Steve

  • 0
    TI__Mastermind 24305 points

    I believe most of the registers will retain their value. Please refer to pages 401-406 of the User's Guide which is the RTC register description. There is a "rw" or "rw-0" under each bit which indicates it's properties, and any initial conditions on PUC or POR. These initial condition descriptors are on page 20. Based on the Calendar mode register description the values are retained. However some registers for this module do reset their values. All in all it will depend on the mode you use.

  • 0 in reply to Brandon08
    Prodigy 110 points

    Thanks, this apepars to answer my main concern.  Just for clarification, I assume that the description "unchanged" means to imply that in the case of Brownout / supply voltage supervisor resets, the value cannot be assumed to be reliable because the power supply was not reliable?

  • 0 in reply to Steven Crawford
    Expert 1235 points

    Hi Brandon,

    There are many RTC registers for which the initial state is being mentioned as "undefined" in the datasheet. Does this mean the initial state will be undefined after a POR or after a PUC ?

    Many of the RTC registers seem to get reset on POR and NOT PUC. But if you see Section 1.2 of the user guide, you will see that a hard reset (low on RST pin) will generate a BOR. The BOR will in turn generate a POR. Therefore if I reset the MSP using the reset pin, the RTC should get reset. It will also get reset if the supply goes below the BOR limits. However it will not get reset if a watchdog timer expires, since it generates only a PUC.

    Regards,

    Praval

  • 0 in reply to Praval Jain
    Intellectual 645 points

    i have copied this note from SLAU259B:

    NOTE: Real-time clock initialization
    Most RTC_A module registers have no initial condition. These registers must be configured
    by user software before use.

    so i think you should re-initialize your RTC after a Reset or Brownout

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