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
A low-power analog continuously operating clock monitor is provided to ensure that LFCLK is running when it is not sourced internally (for example, when LFCLK is sourced from LFXT or LFCLK_IN and not from LFOSC). The LFCLK monitor is only intended to check for clock stuck faults. It is not intended to be used to verify that the frequency of LFCLK is within a specific tolerance.
The LFCLK monitor is disabled at startup after a BOOTRST, unless the cause of the BOOTRST was the NRST pin.
If the STARTLFXT bit in the LFXTCTL register is set, the LFCLK monitor monitors the LFXT. If the STARTLFXT bit is left cleared, the LFCLK monitor monitors the LFCLK_IN.
Before enabling the LFCLK monitor, make sure that the source clock has started and is operating at 32kHz. If STARTLFXT is set and the monitor is checking the LFXT, wait for the LFXTGOOD indication before enabling the LFCLK monitor. If STARTLFXT is cleared and the monitor is checking the LFCLK_IN digital clock input, make sure that the external clock signal is active before enabling the LFCLK monitor. If a valid clock is not present when starting the monitor, the monitor will assert a fault.
The LFCLK continuous monitor can be enabled by setting the MONITOR bit in LFCLKCFG register.
If an LFCLK stuck fault is detected, the system responds in one of two ways depending on the system clock configuration:
In the event that an LFXT or LFCLK_IN failure is detected and the failure is due to a system level / PCB level issue that is preventing the external clock source from being able to run reliably, it is possible to fall back to the internal 32kHz LFOSC rather then continuously trying to use the LFXT or LFCLK_IN. In this case, the following procedure is recommended: