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MSP430FR6972: RTC module calender mode monthly time shift

Kz777
Expert 7895 points

Part Number: MSP430FR6972

Hi Champs,

We would like to use MSR430FR6x RTC calender and watch time shift per monthly.

How many times shift per monthly use case ?

Regards,

Kz777

  • 0
    TI__Guru**** 223817 points
    Hi Kz777,

    Can you please further explain what you are trying to accomplish? The MSP430FR6972 includes a RTC_C with calendar functionality which makes date/time customization straightforward, do you need to set a real-time clock alarm function (Section 29.2.3 of the User's Guide) and update the RTC settings in the ISR accordingly?

    Regards,
    Ryan
  • 0 in reply to Ryan Brown1
    TI__Expert 7895 points
    Hi Ryan,
    Sorry for giving you confuse. I would like to make sure how much shift time per monthly when we use RTC_C calender function.
  • 0 in reply to Kz777
    TI__Guru**** 223817 points
    "How many times shift per monthly use case" and "how much shift time per monthly" are the parts I do not understand, please clarify. The number of days in a month is dependent on which month it is, and leap years are accounted for as well.

    Thanks,
    Ryan
  • 0 in reply to Kz777
    Guru 92251 points

    Kz777 said:
    I would like to make sure how much shift time per monthly when we use RTC_C calender function.

    Do you mean the accuracy of the RTC timekeeping over a month of operation?

    If so, that depends upon the accuracy of the crystal frequency. The MSP430FR6972 has calibration logic that allows for adjusting the crystal frequency in approximately +4-ppm or –2-ppm steps, allowing for higher time keeping accuracy from standard crystals. See section 28.2.5 Real-Time Clock Calibration in the MSP430FR58xx, MSP430FR59xx, and MSP430FR6xx Family User's Guide SLAU367N.

  • 0 in reply to Ryan Brown1
    TI__Expert 7895 points
    Hi Ryan,
    Thanks for your input. Please calcurate 31days in this case. i.e) Janualy

    Regards,
    Kz777
  • 0 in reply to Kz777
    TI__Expert 7895 points
    Hi Ryan,

    Let me confirm if my calcuration correct.
    i.e) accourding to user's guide , this shift is -2 to 4ppm
    i)4.34ppm shift case
    x=(4.34x60x60)/1e+6.
    =+0.015624sec per 60min(3600sec).
    RTC_B is always calibrate per 60min.
    If we calcurate 31day time shift.
    +0.01562sec x 24hour x 31 = +11.62sec

    ii)-2.17ppm
    x=(-2.17x60x60)/1e+6
    =-0.007812 per 60min (3600sec)
    31day
    -0.007812x24x31=-5.8sec.
    So, RTC_B itself shift -5.8 to 11.62sec per mont.

    Is this correct ? I understand it should add crystal ppm also.

    Regards,
    Kz777
  • 0 in reply to Kz777
    TI__Guru**** 223817 points
    Thanks Chester for clearing up my confusion.

    Hi Kaz,

    You misunderstand the User's Guide. The RTC_B module is capable of adjusting the crystal frequency in +4 or -2 ppm steps, but standard frequency tolerance is dependent on the specific crystal used (typically 10 to 20 ppm) and varies with temperature and board design. You should use Section 28.2.5 as a guide for using the RTCCALS and RTCCALx bits to adjust the crystal per unit. Please refer to the following E2E posts and SLAA322:

    e2e.ti.com/.../376650
    e2e.ti.com/.../302580
    www.ti.com/.../slaa322c.pdf

    Regards,
    Ryan

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