12.2 Clock Switching

The system clock source can be switched between external and internal clock sources via software using the New Oscillator Source Request (NOSC) and New Divider Selection Request (NDIV) bits. The following sources can be selected:
  • External Oscillator (EXTOSC)
  • EXTOSC with 4x PLL
  • High-Frequency Internal Oscillator (HFINTOSC)
  • Low-Frequency Internal Oscillator (LFINTOSC)
  • Secondary Oscillator (SOSC)
The Clock Switch Enable (CSWEN) Configuration bit can be used to enable or disable the clock switching capability. When CSWEN is set (CSWEN = 1), writes to NOSC and NDIV by user software will allow the system clock to switch between sources or frequencies. When CSWEN is clear (CSWEN = 0), writes to NOSC and NDIV are ignored, preventing the system clock from switching from one source to another.