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RTC after reset

Eric Jonardi
Intellectual 305 points


The FR75xx family guide states that there is no initial state for the timekeeping (seconds, minutes, etc.) registers of the RTC_B module. Does this mean that the values of these registers will preserved without corruption after A) a watchdog timer expire or B) a software BOR?    (assuming in both cases that power is not lost)

Thanks,

Eric Jonardi

  • 0
    Guru 227245 points

    If the registers aren't reset to any initial state on BOR or PUC (WDT reset), then they should keep their old state unless power is lost. I didn't test it (I use the RTC in the MSP5438 as timer for multitasking rather than for timekeeping - I use an external I2C RTC for that). However, you should be able to test it: Write a program that sends the current RTC value to the PC and then does a reset. Over and over again. and on the PC you check whether there is a drift or distortion between the receive time and the received value.

  • 0 in reply to Jens-Michael Gross
    Intellectual 305 points

    Thanks, that's a good suggestion on testing it. My only other concern would be how this might perform at the extreme ends of a -40 to 90C temperature spectrum, as this is the likely temperature swing that I will see.

  • 0 in reply to Eric Jonardi
    Guru 227245 points

    Eric Jonardi said:
    My only other concern would be how this might perform at the extreme ends of a -40 to 90C temperature spectrum, as this is the likely temperature swing that I will see.

    Whew, that's really stressing the whole system (I think about thermal stress by material expansion and contraction. Havign many cycles that large will probably rip your parts from the PCB)

    About the test, well if the test succeeds, the temperature coefficient of the crystal will be a much greater problem than a possible short stop (a missing count) during a reset.

  • 0 in reply to Jens-Michael Gross
    Intellectual 305 points

    Missing a count from the crystal isn't so much of a concern as is loosing the value of the register. The RTC will be used to time stamp events in a cubesat (http://en.wikipedia.org/wiki/CubeSat) being constructed by Marquette university, so knowing the time (within an moderate error range) is crucial for timing orbital passes.

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