12.3.3 Fail-Safe Operation - Primary and Secondary Fail-Safe Clock Monitors
When the primary external clock (EXTOSC) or the secondary external clock (SOSC) fail, the
Oscillator Fail Interrupt Flag (OSFIF) bit of the PIR registers will be set.
Additionally, the corresponding FSCM failure status bit (FSCMPEV or FSCMSEV, respectively) will be set. If the Oscillator Fail
Interrupt Enable (OSFIE) bit has been set, an interrupt will be generated
when OSFIF is high. It is important to note that neither the primary or
secondary Fail-Safe Clock Monitors will cause a clock switch to occur in the
event of a failure, and it is up to the user to address the clock fail
event.