Datasheet

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 DFLLCTRL.RUNSTDBY bit is one. If
DFLLCTRL.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 DFLL behaves during standby sleep mode:
Value Description
0
The oscillator is disabled in standby sleep mode.
1
The oscillator is not stopped in standby sleep mode. If DFLLCTRL.ONDEMAND is one, the
clock source will be running when a peripheral is requesting the clock. If
DFLLCTRL.ONDEMAND is zero, the clock source will always be running in standby sleep
mode.
Bit 5 – USBCRM USB Clock Recovery Mode
Value Description
0
USB Clock Recovery Mode is disabled.
1
USB Clock Recovery Mode is enabled.
Bit 4 – LLAW Lose Lock After Wake
Value Description
0
Locks will not be lost after waking up from sleep modes if the DFLL clock has been stopped.
1
Locks will be lost after waking up from sleep modes if the DFLL clock has been stopped.
Bit 3 – STABLE Stable DFLL Frequency
Value Description
0
FINE calibration tracks changes in output frequency.
1
FINE calibration register value will be fixed after a fine lock.
Bit 2 – MODE Operating Mode Selection
Value Description
0
The DFLL operates in open-loop operation.
1
The DFLL operates in closed-loop operation.
Bit 1 – ENABLE DFLL Enable
Due to synchronization, there is delay from updating the register until the peripheral is enabled/disabled.
The value written to DFLLCTRL.ENABLE will read back immediately after written.
Value Description
0
The DFLL oscillator is disabled.
1
The DFLL oscillator is enabled.
SAM D21 Family
SYSCTRL – System Controller
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 223