Datasheet
Note:
1. Number of cycles for the start-up counter
2. Number of cycles for the synchronization delay, before PCLKSR.XOSCRDY is set.
3. Actual start-up time is n OSCULP32K cycles + 3 XOSC cycles, but given the time neglects the 3
XOSC cycles.
Bit 11 – AMPGC Automatic Amplitude Gain Control
This bit must be set only after the XOSC has settled, indicated by the XOSC Ready flag in the PCLKSR
register (PCLKSR.XOSCRDY).
Value Description
0
The automatic amplitude gain control is disabled.
1
The automatic amplitude gain control is enabled. Amplitude gain will be automatically
adjusted during Crystal Oscillator operation.
Bits 10:8 – GAIN[2:0] Oscillator Gain
These bits select the gain for the oscillator. The listed maximum frequencies are recommendations, and
might vary based on capacitive load and crystal characteristics. Setting this bit group has no effect when
the Automatic Amplitude Gain Control is active.
GAIN[2:0] Recommended Max Frequency
0x0 2MHz
0x1 4MHz
0x2 8MHz
0x3 16MHz
0x4 30MHz
0x5-0x7 Reserved
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 XOSC.ONDEMAND bit has been previously written to one, the
oscillator will be running only 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 XOSC.RUNSTDBY bit is one. If
XOSC.RUNSTDBY is zero, the oscillator is disabled.
Value Description
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 oscillator is disabled if no peripheral is requesting the clock source.
Bit 6 – RUNSTDBY Run in Standby
This bit controls how the XOSC behaves during standby sleep mode:
SAM D21 Family
SYSCTRL – System Controller
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 211