4.15.4.1 Switching from Embedded Always-on 64 kHz RC Oscillator to 32.768 kHz Crystal Oscillator

The sequence to switch from the embedded Always-on 64 kHz (typical) slow RC oscillator to the 32.768 kHz crystal oscillator is the following:

1. Switch the main system bus clock to a source different from slow clock (PLL or Main Oscillator) through the Power Management Controller.
2. Switch from the embedded Always-on 64 kHz RC oscillator to the 32.768 kHz crystal oscillator by writing a 1 to the TD_OSCSEL bit.
3. Wait 5 slow clock cycles for internal resynchronization.