Data Sheet

192
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181G–SAM-D21_Datasheet–09/2015
z Bits 27:16 – CALIB[11:0]: Oscillator Calibration
These bits control the oscillator calibration. The calibration field is split in two:
CALIB[11:6] is for temperature calibration
CALIB[5:0] is for overall process calibration
These bits are loaded from Flash Calibration at startup.
z Bits 15:10 – Reserved
These bits are unused and reserved for future use. For compatibility with future devices, always write these bits to
zero when this register is written. These bits will always return zero when read.
z Bits 9:8 – PRESC[1:0]: Oscillator Prescaler
These bits select the oscillator prescaler factor setting according to the table below.
Table 16-12. Oscillator Prescaler
z 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.
0: The oscillator is always on, if enabled.
1: The oscillator is enabled when a peripheral is requesting the oscillator to be used as a clock source. The oscilla-
tor is disabled if no peripheral is requesting the clock source.
z Bit 6 – RUNSTDBY: Run in Standby
This bit controls how the OSC8M behaves during standby sleep mode:
0: The oscillator is disabled in standby sleep mode.
1: The oscillator is not stopped in standby sleep mode. If OSC8M.ONDEMAND is one, the clock source will be run-
ning when a peripheral is requesting the clock. If OSC8M.ONDEMAND is zero, the clock source will always be
running in standby sleep mode.
z Bits 5:2 – Reserved
These bits are unused and reserved for future use. For compatibility with future devices, always write these bits to
zero when this register is written. These bits will always return zero when read.
z Bit 1 – ENABLE: Oscillator Enable
0: The oscillator is disabled or being enabled.
1: The oscillator is enabled or being disabled.
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.
PRESC[1:0] Description
0x0 1
0x1 2
0x2 4
0x3 8