The Low Frequency Oscillator is used for the watchdog timer, and to test the functionality of the HFO as described above. As with the High Frequency Oscillator Failure detection, two counters are used to detect a failure with the Low Frequency Oscillator block. The counter roles are reversed in the Low Frequency Oscillator failure detection with the Low Frequency Oscillator clock generating a clear signal once the counter reaches a firmware programmable 5-bit threshold. This clear signal clears the free running High Frequency Oscillator counter. In the case of a Low Frequency Oscillator failure, no clear signal is generated and the High Frequency Oscillator counter will overflow. Firmware can detect the Low Frequency Oscillator Failure through the Fault Mux interrupt or through polling the status register in the Fault Mux Registers. There are three bit fields in the LFOFAILDET register:

• LFO_FAIL_THRESH – Configures threshold where a clear flag is used to clear a counter in the High Frequency Oscillator domain (if HFO counter overflows, a reset will be generated), resolution of threshold equals Low Frequency Oscillator period
• LFO_FAIL_INT_EN – a 1 enables Interrupt Generation upon LFO Failure Detection
• LFO_DETECT_EN – a 1 enables the LFO failure detection circuitry.

There are LFO_FAIL bits in the FAULTMUXRAWSTAT and FAULTMUXINTSTAT registers, giving status of the LFO fault detection status and interrupt status.