10.3.1 Sleep Mode Operation

When a clock source is not used/requested it will turn off. It is possible to request an clock source directly by writing a '1' to the Run Standby bit (RUNSTDBY) in the respective oscillator's Control A register (CLKCTRL.[osc]CTRLA). This will cause the oscillator to run constantly, except for Power Down sleep mode. Additionally, when this bit is written to '1' the oscillator start-up time is eliminated when the clock source is requested by a peripheral.

The Main Clock will always run in Active and Idle sleep mode. In Standby sleep mode, the Main Clock will only run if any peripheral is requesting it, or the Run in Standby bit (RUNSTDBY) in the respective oscillator's Control A register (CLKCTRL.[osc]CTRLA) is written to '1'.

In Power Down sleep mode, the Main Clock will stop after all NVM operations are completed.