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MSP430F6747: Questions for RTC_C

Part Number: MSP430F6747

Hi,

I got questions from customer about RTC_C module in MSP430F6747.

Q1) What is operating voltage range?
I understood RTC_C uses dedicated AUXVCC3 supply, but datasheet does not seem to provide Recommended Operating Conditions for AUXVCC3.
Is this the same as Vcc?

Q2) Is this possible to detect RTC_C stops working in any way?

hanks and regards,
Koichiro Tashiro

  • Hi,

    Q1) What is operating voltage range?

    You can find how to use it in the user guide on page 133. MSP430x5xx and MSP430x6xx Family user guide.pdf

    And in the datasheet, it gives the exact number:

    Q2) Is this possible to detect RTC_C stops working in any way?

    What's your opinion? You want to check the lowest voltage that RTC can work on?

    Maybe you can use a LED to indicate when MCU enter the RTC interrupt.

    Eason

  • Hi Eason,

    Thanks for your quick reply!

    For Q1), I see. Sorry, I referred to an old document.

    For Q2), I got the scenario customer thinks about.
    Suppose the device is in LPM3.5 and only RTC is working and AUXVCC3 power is provided by super capacitor.
    So the power can be maintained for limited period.
    Then the device wakes up from LPM3.5 and power is back. The CPU checks whether RTC has been working properly during LPM3.5 or not.
    If the register values are completely corrupted, we can tell the power is lost and RTC stopped working.

    Customer wonders there might be a case register values are kept, but RTC counter stops counting for a while.
    In such case, it is not easy to tell the RTC needs to be re-initialized or not.
    Does RTC_C module has feature to check above situation happened or not?

    Thanks and regards,
    Koichiro Tashiro

  • Hi,
    1. Now your way to judge whether RTC keeps working is to check whether register value becomes 0.
    2. And you afraid that when RTC counter stops counting for a while and its power lost, you can't judge it correctly?

    My advice:
    1. You can check the register: SYSRSTIV. If is a power on rst, SYSRSTIV will equal to 04h. it means RST/NMI (POR) . Please see the datasheet of MSP430F6747 on page 77.
    2. If you don't care about power consumption and memory size, you can use a sector of information memory(128B) to save the information.

    Eason
  • Hi Eason,

    Sorry for my late reply.

    Customer expects the function something like “BLD” bit in “Status register 1” in below device, for example.

    https://www.ablic.com/en/doc/datasheet/real_time_clock/S35390A_E.pdf

    I guess MSP430 has similar function in PMM, but PMM is disable in LPM3.5, right?

    Thanks and regards,
    Koichiro Tashiro

  • Hi,
    Yes, you are right.
    Just see from the user guide, the SVS and SVM are always disabled in LPMx.5. However, FRAM series support using SVS in LPMx.5.
    The only way is to check SYSRSTIV. If it indicates a power on rst, it means the power was below 1.8V.
    Eason
  • Hi Eason,

    Thanks for your confirmation. I understood.

    Thanks and regards,
    Koichiro Tashiro