Clock Control Logic
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
7-11
7.1.2 Clock Locking
There are two conditions under which clock locking occurs: reset initialization and clock
reprogramming.
7.1.2.1 Reset Initialization
The clock circuits are initialized after the first phase of the reset configuration when the low part
of the reset configuration word is loaded according to the selected clock mode.
7.1.2.2 Clock Reprogramming
The clock circuits can be reprogrammed after the reset configuration stage is completed. Use the
following steps to reprogram the clocks:
1.
Write the new values to the front registers: DCMRnFs, PCMRnFs and PAMRnFs.
Select a new clock mode and write its parameters to the front registers. You must write
values to ALL the front registers. Register values for each clock mode are listed in
Table 7-13 Clock Mode Register Reprogramming Values, on page 7-25.
Note:
The values listed for PCMR0 assume that the GP_CTL field = 000. This field can be
changed, subject to the restrictions in this chapter.
2.
Set SCCR[RLKPLL] and SCCR[RLKDIV] to activate the new settings.
Note:
Setting the SCCR[RLKPLL] and SCCR[RLKDIV] bits activates the relock sequence.
3.
After the clock relocks, you must clear the relock bits (SCCR[RLKPLL] and
SCCR[RLKDIV]) by writing zeros to them.
4.
Initiate an internal soft reset.
Note:
During clock relocking, all system clocks are stopped. Some circuits in the system may
require an oscillating clock to be reset.Therefore, either do not assert a hard or soft
reset during the relock sequence, or extend the assertion of the reset signal (
HRESET
or
SRESET
) for several
CLKIN
cycles after
CLKOUT
has started oscillating again. There is no
restriction regarding
PORESET
during relock.
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