27.4.3 Switching from 32.768 kHz Crystal Oscillator to Embedded 32 kHz RC Oscillator

The sequence to switch from the 32.768 kHz crystal oscillator to the embedded 32 kHz (typical) RC oscillator is the following:

1. Switch the main system bus clock to a source different from slow clock (PLL or Main Oscillator).
2. Switch from the 32.768 kHz crystal oscillator to the embedded RC oscillator by writing a 0 to the TD_OSCSEL bit.
3. Wait 5 slow clock cycles for internal resynchronization.
4. Disable the 32.768 kHz crystal oscillator by writing a 0 to the OSC32EN bit.