If External Oscillator or XCLKIN or Internal Oscillator 2 (OSCCLKSRC2) is selected and a missing clock is
detected, the missing clock detect circuit will automatically switch to Internal Oscillator 1 (OSCCLKSRC1)
and generate a CLOCKFAIL signal. In addition, the PLLCR register is forced to zero (PLL is bypassed) to
prevent any potential overshoot. The user can then write to the PLLCR register to re-lock the PLL. Under
this situation, the missing clock detect circuit will be automatically re-enabled (PLLSTS[MCLKSTS] bit will
be automatically cleared). If Internal Oscillator 1 (OSCCLKSRC1) should also fail, then under this
situation, the missing clock detect circuit will remain in limp mode. The user will have to re-enable the logic
via the PLLSTS[MCLKCLR] bit.