DPLLCTRLB.LTIME=0, the lock signal is linked with the status bit of the DPLL, and the lock time varies
depending on the filter selection and the final target frequency.
When the Wake Up Fast bit (DPLLCTRLB.WUF) is set, the wake up fast mode is activated. In this mode
the clock gating cell is enabled at the end of the startup time. At this time the final frequency is not stable,
as it is still during the acquisition period, but it allows to save several milliseconds. After first acquisition,
the Lock Bypass bit (DPLLCTRLB.LBYPASS) indicates if the lock signal is discarded from the control of
the clock gater (CG) generating the output clock CLK_DPLL.
Table 21-3. CLK_DPLL Behavior from Startup to First Edge Detection
WUF
LTIME
CLK_DPLL Behavior
0
0
Normal Mode: First Edge when lock is asserted
0
Not Equal To Zero Lock Timer Timeout mode: First Edge when the timer down-counts to 0.
1
X
Wake Up Fast Mode: First Edge when CK is active (startup time)
Table 21-4. CLK_DPLL Behavior after First Edge Detection
LBYPASS
CLK_DPLL Behavior
0
Normal Mode: the CLK_DPLL is turned off when lock signal is low.
1
Lock Bypass Mode: the CLK_DPLL is always running, lock is irrelevant.
Figure 21-4. CK and CLK_DPLL Output from DPLL Off Mode to Running Mode
CKR
ENABLE
CK
LOCK
CK STABLE
t
startup_time
t
lock_time
CLK_DPLL
Reference Clock Switching
When a software operation requires reference clock switching, the recommended procedure is to turn the
DPLL into the standby mode, modify the DPLLCTRLB.REFCLK to select the desired reference source,
and activate the DPLL again.
Output Clock Prescaler
The DPLL controller includes an output prescaler. This prescaler provides three selectable output clocks
CK, CKDIV2 and CKDIV4. The Prescaler bit field in the DPLL Prescaler register (DPLLPRESC.PRESC)
is used to select a new output clock prescaler. When the prescaler field is modified, the
DPLLSYNCBUSY.DPLLPRESC bit is set. It will be cleared by hardware when the synchronization is over.
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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