Watchdog Clock Source Select Bit: This bit selects the source for WDCLK. On XRS low
and after XRS goes high, internal oscillator 1 is selected by default. User would need to
select external oscillator or Internal Oscillator 2 during their initialization process. If missing
clock detect circuit detects a missing clock, then this bit is forced to 0 and internal oscillator
1 is selected. The user changing this bit does not affect the PLLCR value.