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MB90420/5 (A) SERIES F
MC-16LX FAMILY 16-BIT MICROCONTROLLERS HARDWARE MANUAL
4.5 Oscillation Stabilization Wait Time
At power-on, canceling stop mode, or switching from the sub-clock to the main clock or to the PLL clock, the
oscillation of the oscillation clock is stopped, so the oscillation stabilization wait time is required after
oscillation is started. At switching from the main clock to the PLL clock, the oscillation stabilization wait time
is also required after PLL oscillation is started.
n Oscillation stabilization wait time
Oscillator such as ceramic or crystal requires a few ms to several ten ms from when oscillation starts until
oscillation stabilizes at the original frequency. Consequently, the CPU operation is disabled immediately
after oscillation starts, and then the clock is supplied to the CPU when the oscillation stabilization wait time
has elapsed and oscillation is well-stabilized.
The time required for oscillation to stabilize depends on the type of the oscillator (crystal, ceramic, etc.,) so
the appropriate oscillation stabilization wait time must be selected for the oscillator type. The oscillation
stabilization wait time can be selected by setting the clock select register (CKSCR). At switching from the
main clock to the PLL clock, the CPU operates on the main clock during the PLL oscillation stabilization wait
time, and then switches from the main clock to the PLL clock.
Figure 4.5 shows the operation immediately after the oscillation started.
Normal operation started
or
Oscillation stabilization
Oscillation time of oscillator
switching to PLL clock
wait time
X1
The oscillation
The oscillation
started
stabilized
Fig. 4.5 Operation Immediately After Oscillation Started
4-12
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