SLAU847D October 2022 – May 2024 MSPM0L1105 , MSPM0L1106 , MSPM0L1227 , MSPM0L1228 , MSPM0L1228-Q1 , MSPM0L1303 , MSPM0L1304 , MSPM0L1304-Q1 , MSPM0L1305 , MSPM0L1305-Q1 , MSPM0L1306 , MSPM0L1306-Q1 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346 , MSPM0L2227 , MSPM0L2228 , MSPM0L2228-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%.
It is possible to check for a valid clock signal on LFCLK_IN by enabling the LFCLK monitor before setting SETUSEEXLF in the EXLFCTL register. By default, the LFCLK monitor will check LFCLK_IN if the LFXT was not started.
After LFCLK_IN is selected as the LFCLK source, it is not possible to change back to LFOSC or LFXT without going through a BOOTRST.