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MSP430FR5969: RTC Backup Clock Source.. If LFXIN/LFXOUT and then LFXTCLK Fails..

Newman
Expert 5945 points
Part Number: MSP430FR5969

Hi Team MSP,

It seems that the FR5969 RTC_B can only be sourced from LFXTCLK (from an external xtal w/ LFXIN/LFXOUT).  Usually MSP430 devices have a backup clock that auto-enables when a primary clock source fails.. for pretty much all peripherals. 

Does the RTC_B peripheral have a backup clock source if the crystal(LFXIN/LFXOUT) -> LFXTCLK fails?

Thanks, Merril

Ref:

https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/990124/msp430fr5969-rtc-clock-source

  • 0
    TI__Guru 68011 points

    Hi Merril,

    That sounds right.  The TRM shows only the LFXTCLK as the clock source for RTC_B, and should that fail there is no mechanism to detect it and no other clock that is designated as a backup.  Is this a customer question or issue?

  • 0 in reply to Dennis Lehman
    TI__Expert 5945 points

    Hi Dennis,

    Thx!  A customer ask.. looking for & wanting a backup if the XTAL fails..

  • 0 in reply to Newman
    TI__Guru 68011 points

    Hi Merril,

    You probably already saw this in the TRM. I forgot to add to the post.

  • 0 in reply to Newman
    TI__Expert 5945 points

    Hi Dennis,

    Thx!  This seems to support the fact that there is no backup clock for RTC, right?  Since the TRM says "If LFXT is sourcing any system clock (ACLK, MCLK, or SMCLK) and a fault is detected, the system clock is automatically switched to LFMODCLK for its clock source.".. so that provides backup for ACLK/MCLK/SMCLK.. but no backup clock for LFXT.. and then LFXT driving the RTC directly has no backup (for the RTC peripheral), right?  This means that if LFXT fails.. the RTC will not function at all, right?

    Thanks, Merril

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