OSC16M is used as a clock source for the generic clock generators. This is configured by the Generic
Clock Generator Controller.
Related Links
GCLK - Generic Clock Controller
on page 121
21.6.5. Digital Frequency Locked Loop (DFLL48M) Operation
The DFLL48M can operate in both open-loop mode and closed-loop mode. In closed-loop mode, a low-
frequency clock with high accuracy should be used as the reference clock to get high accuracy on the
output clock (CLK_DFLL48M).
The DFLL48M can be used as a source for the generic clock generators.
Related Links
GCLK - Generic Clock Controller
on page 121
21.6.5.1. Basic Operation
Open-Loop Operation
After any reset, the open-loop mode is selected. When operating in open-loop mode, the output
frequency of the DFLL48M clock, CLK_DFLL48M, will be determined by the values written to the DFLL
Coarse Value bit group and the DFLL Fine Value bit group (DFLLVAL.COARSE and DFLLVAL.FINE) in
the DFLL Value register. Using "DFLL48M COARSE CAL" value from the Non Volatile Memory Software
Calibration Area in DFLL.COARSE helps to output a frequency close to 48MHz.
It is possible to change the values of DFLLVAL.COARSE and DFLLVAL.FINE while the DFLL48M is
enabled and in use, and thereby to adjust the output frequency of CLK_DFLL48M.
Related Links
on page 40
Closed-Loop Operation
In closed-loop operation, the DFLL48M output frequency is continuously regulated against a precise
reference clock of relatively low frequency. This will improve the accuracy and stability of the
CLK_DFLL48M clock in comparison to the open-loop (free-running) configuration.
Before closed-loop operation can be enabled, the DFLL48M must be enabled and configured in the
following way:
1.
Enable and select a reference clock (CLK_DFLL48M_REF). CLK_DFLL48M_REF is Generic Clock
Channel 0 (DFLL48M_Reference).
2.
Select the maximum step size allowed for finding the Coarse and Fine values by writing the
appropriate values to the DFLL Coarse Maximum Step and DFLL Fine Maximum Step bit groups
(DFLLMUL.CSTEP and DFLLMUL.FSTEP) in the DFLL Multiplier register.
A small step size will ensure low overshoot on the output frequency, but it will typically take longer
until locking is achieved. A high value might give a large overshoot, but will typically provide faster
locking.
DFLLMUL.CSTEP and DFLLMUL.FSTEP should not be higher than 50% of the maximum value of
DFLLVAL.COARSE and DFLLVAL.FINE, respectively.
3.
Select the multiplication factor in the DFLL Multiply Factor bit group (DFLLMUL.MUL) in the DFLL
Multiplier register.
Note:
When choosing DFLLMUL.MUL, the output frequency must not exceed the maximum
frequency of the device.
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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