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MSP430FR59941: RTC without using crystal

Danilo A.
Mastermind 27650 points
Part Number: MSP430FR59941
Other Parts Discussed in Thread: MSP430FR5994

Hi Team,

Our customer would like to confirm if it is possible to use the RTC of MSP430FR5994 without using an external crystal. I understand that the clock source for the RTC could come from the 16MHz or 32.768kHz crystal as explained in the application note below.

https://www.ti.com/lit/an/spracv5/spracv5.pdf

However, according to our customer he is getting the RTC output without using the crystal. Can you please tell what could be the reason for this?

Regards,

Danilo

  • 0
    TI__Guru 56685 points

    Hello,

    VLOCLK or LFMODCLK would be the clock for ACLK which feeds the RTC when there is no external xtal. See section 3.2.8 in the family user guide. 

  • 0 in reply to Jace H
    TI__Mastermind 27650 points

    Hi Jace,

    Thank you for this information. I understand  that the VLO frequency may decrease in LPM3 or LPM4 mode as mentioned at  Section 8.12.3.4 of the datasheet, hence it can't be use as accurate source of clock for RTC. Can you please confirm?

    Regards,

    Danilo

  • +1 in reply to Danilo A.
    TI__Guru 56685 points

    Hello,

    Correct. It is not as accurate as the datasheet suggests. Useful if you just need to wakeup the MCU at some point, but not necessarily at a certain time. 

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