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Chapter 4
Clock Generator
Preliminary User’s Manual U17566EE1V2UM00
Since CLMCS.CMRT = 1 is synchronized with the ring oscillator any change of
this bit has to be maintained for at least 65 ring oscillator periods T
ROSC
= 1/
f
ROSC
to become effective. Therefore a wait period has to be assured before
this bit is changed again.
Proceed as follows to start the sub oscillator clock monitor:
1. After reset enable sub oscillator clock monitor:
PRCMDCM = FF
H
permit write to CLMS
CLMS.CLMES = 1enable sub oscillator clock monitor
2. Make sure the sub oscillator is stable.
3. Start sub oscillator clock monitor after reset and after power save mode
wake-up:
CLMCS.CMRT = 1
4. Wait for 65 ring oscillator periods T
ROSC
before resetting CMRT:
wait (65 x max(T
ROSC
))
5. Clear
CLMCS.CMRT:
CLMCS.CMRT = 0
6. Before CMRT should be set to 1 again, wait for 65 ring oscillator periods
T
ROSC
:
wait (65 x max(T
ROSC
))
Note that the minimum ring oscillator frequency min(f
ROSC
) (max(T
ROSC
)) has
to be taken into account for the wait time in steps (3) and (5).
Caution
The sub oscillator clock monitor is sometimes already started by setting
CLMS.CLMES = 1, i.e. without CLMCS.CMRT = 1.
In these cases it would not be required to start the sub oscillator by setting
CLMCS.CMRT = 1 additionally.
Since it is unpredictable whether the clock monitor has already started after
CLMS.CLMES = 1 the procedure described above should be followed in any
case.
(3)
Operation during and after power save modes
Main oscillator
stopped
If the main oscillator is stopped, its clock monitor changes to stand-by. When
the main oscillator is restarted after power save mode release, the main
oscillator clock monitor restarts automatically.
Sub oscillator
stopped
If the sub oscillator is stopped, its clock monitor stops.
When the sub oscillator is restarted after power save mode release, the sub
oscillator clock monitor does not start automatically.
Software must ensure that the sub oscillator stabilization time has elapsed and
then start the monitor by setting CLMCS.CMRT to 1.
Ring oscillator
stopped
If the ring oscillator is stopped, both clock monitors’ operation is suspended.
Their operation is automatically resumed as soon as the ring oscillator is
restarted.
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