The LPO Clock Detect (LPOCLKDET) module consists of a clock monitor (CLKDET) and an internal low-power oscillator (LPO).
The LPO provides two different clock sources – a low frequency (LFLPO) and a high frequency (HFLPO).
The CLKDET is a supervisor circuit for an externally supplied clock signal (OSCIN). In case the OSCIN frequency falls out of a frequency window, the CLKDET flags this condition in the global status register (GLBSTAT bit 0: OSC FAIL) and switches all clock domains sourced by OSCIN to the HFLPO clock (limp mode clock).
The valid OSCIN frequency range is defined as: fHFLPO / 4 < fOSCIN < fHFLPO * 4.