16.6.3. Peripheral Clock
Figure 16-4. Peripheral Clock
16.6.3.1. Enabling a Peripheral Clock
Before a Peripheral Clock is enabled, one of the Generators must be enabled (GENCTRLn.GENEN) and
selected as source for the Peripheral Channel by setting the Generator Selection bits in the Peripheral
Channel Control register (PCHCTRL.GEN). Any available Generator can be selected as clock source for
each Peripheral Channel.
When a Generator has been selected, the peripheral clock is enabled by setting the Channel Enable bit in
the Peripheral Channel Control register, PCHCTRLm.CHEN = 1. The PCHCTRLm.CHEN bit must be
synchronized to the generic clock domain. PCHCTRLm.CHEN will continue to read as its previous state
until the synchronization is complete.
16.6.3.2. Disabling a Peripheral Clock
A Peripheral Clock is disabled by writing PCHCTRLm.CHEN=0. The PCHCTRLm.CHEN bit must be
synchronized to the Generic Clock domain. PCHCTRLm.CHEN will stay in its previous state until the
synchronization is complete. The Peripheral Clock is gated when disabled.
Related Links
on page 138
16.6.3.3. Selecting the Clock Source for a Peripheral
When changing a peripheral clock source by writing to PCHCTRLm.GEN, the peripheral clock must be
disabled before re-enabling it with the new clock source setting. This prevents glitches during the
transition:
1.
Disable the Peripheral Channel by writing PCHCTRLm.CHEN=0
2.
Assert that PCHCTRLm.CHEN reads '0'
3.
Change the source of the Peripheral Channel by writing PCHCTRLm.GEN
4.
Re-enable the Peripheral Channel by writing PCHCTRLm.CHEN=1
Related Links
on page 138
16.6.3.4. Configuration Lock
The peripheral clock configuration can be locked for further write accesses by setting the Write Lock bit in
the Peripheral Channel Control register PCHCTRLm.WRTLOCK=1). All writing to the PCHCTRLm
register will be ignored. It can only be unlocked by a Power Reset.
The Generator source of a locked Peripheral Channel will be locked, too: The corresponding GENCTRLn
register is locked, and can be unlocked only by a Power Reset.
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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