SLAU846B June 2023 – November 2024 MSPM0G1105 , MSPM0G1106 , MSPM0G1107 , MSPM0G1505 , MSPM0G1506 , MSPM0G1507 , MSPM0G3105 , MSPM0G3106 , MSPM0G3107 , MSPM0G3505 , MSPM0G3506 , MSPM0G3507
The RTC is clocked directly from RTCCLK, which is sourced either from the internal LFOSC or the external low frequency crystal oscillator (LFXT). The LFOSC and LFXT both require startup time. Ensure that the oscillator sourcing LFCLK in the application is configured and that LFCLK is operational before enabling power to the RTC module.
Two prescale dividers, RT0PS and RT1PS, are automatically configured to provide a 1-second clock interval for the RTC. The LFCLK must be running at 32kHz clock frequency for proper RTC operation. The RT0PS divider is sourced directly from LFCLK at 32kHz. The output of the RT0PS divider block is 32kHz/256, or 128Hz, and is used to source the input of the RT1PS divider block. The RT1PS output is 128Hz/128, or 1Hz, and is used to source the real-time clock counter registers with the required 1-second time interval.
Clearing the MODCLKEN bit in the CLKCTL register of the RTC halts the propagation of LFCLK to the real-time counters and the prescale counters (RT0PS and RT1PS) in the RTC. It does not have any effect on the LFCLK itself.