# Clock Failure Detection (CFD)

The Clock Failure Detection (CFD) allows the device to continue operating if an external crystal oscillator or clock source fails. The CFD is enabled by writing a ‘1’ to the Clock Failure Detection Enable (CFDEN) bit in the Main Clock Control C (CLKCTRL.MCLKCTRLC) register. See the Clock Failure Detection (CFD) Block Diagram for monitorable oscillators and clock sources.