SLAU962A December 2025 – June 2026 MSPM33C321A , MSPM33C321A-Q1
It is possible to bypass the LFXT circuit and bring in a 32.768kHz typical frequency digital clock into the device to use as the LFCLK source instead of LFOSC or LFXT. To configure LFCLK to use a digital clock input instead of LFXT or LFOSC, first configure the IOMUX to enable the LFCLK_IN function on the appropriate pin. When IOMUX is configured correctly and the external clock source is outputting a 32kHz clock to LFCLK_IN, set the SETUSEEXLF bit in the EXLFCTL register in SYSCTL.
LFCLK_IN is compatible with digital square wave CMOS clock inputs and should have a typical duty cycle of 50%.
When the system is initialized, LFOSC is the primary clock source for LFCLK. Before switching LFCLK to use LFCLK_IN, it is possible to check for a valid clock signal on LFCLK_IN by enabling the LFCLK monitor through setting the MONITOR bit in LFCLKCFG register.
After LFCLK_IN is selected as the LFCLK source, it is not possible to change back to LFOSC or LFXT without going through a BOR reset.