17.3.10 Fail-Safe Clock Monitor (FSCM)

The clock system includes a Fail-Safe Clock Monitor (FSCM). The FSCM monitors the SYS_CLK for continuous operation. If the SYS_CLK fails, it switches the SYS_CLK over to the FRC oscillator and triggers an NMI. The FRC is an untuned 8 MHz oscillator that drives the SYS_CLK during an FSCM event. If executing the NMI, software can restart the main oscillator or shut down the system.

The SYS_CLK and the FSCM halt in the Sleep modes to prevent FSCM detection.