Fail-Safe Detection

The FSCM detects a failed oscillator by comparing the external oscillator to the FSCM sample clock. The sample clock is generated by dividing the LFINTOSC by 64. The fail detector block contains a latch that is set upon each falling edge of the external clock. The latch is cleared on the rising edge of the sample clock. A failure is detected when a half-period of the sample clock elapses before the external clock goes low.