Datasheet

PRESC[1:0] Description

0x0 1

0x1 2

0x2 4

0x3 8

Bit 7 – ONDEMAND On Demand Control

The On Demand operation mode allows an oscillator to be enabled or disabled depending on peripheral

clock requests.

In On Demand operation mode, i.e., if the ONDEMAND bit has been previously written to one, the

oscillator will only be running when requested by a peripheral. If there is no peripheral requesting the

oscillator's clock source, the oscillator will be in a disabled state.

If On Demand is disabled the oscillator will always be running when enabled.

In standby sleep mode, the On Demand operation is still active if the OSC8M.RUNSTDBY bit is one. If

OSC8M.RUNSTDBY is zero, the oscillator is disabled.

Value Description

The oscillator is always on, if enabled.

The oscillator is enabled when a peripheral is requesting the oscillator to be used as a clock

source. The oscillator is disabled if no peripheral is requesting the clock source.

Bit 6 – RUNSTDBY Run in Standby

This bit controls how the OSC8M behaves during standby sleep mode:

Value Description

The oscillator is disabled in standby sleep mode.

The oscillator is not stopped in standby sleep mode. If OSC8M.ONDEMAND is one, the

clock source will be running when a peripheral is requesting the clock. If

OSC8M.ONDEMAND is zero, the clock source will always be running in standby sleep

mode.

Bit 1 – ENABLE Oscillator Enable

The user must ensure that the OSC8M is fully disabled before enabling it, and that the OSC8M is fully

enabled before disabling it by reading OSC8M.ENABLE.

Value Description

The oscillator is disabled or being enabled.

The oscillator is enabled or being disabled.

SAM D21 Family

SYSCTRL – System Controller

Datasheet Complete

DS40001882D-page 221