Oscillation Stabilization Wait Time - Fujitsu F2MC-16LX Hardware Manual

5.5

Oscillation Stabilization Wait Time

When the power is turned on, when stop mode is released, or switching from the sub-
clock to the main clock or from sub-clock to the PLL clock occurs, an oscillation
stabilization wait time is required after oscillation begins because the oscillation clock
is stopped. When switching from the main clock to the PLL clock or from the main
clock to the sub-clock occurs, an oscillation stabilization wait time is required.
I Oscillation stabilization wait time
Ceramic and crystal oscillators generally require a waiting time ranging from several
milliseconds to several ten milliseconds after the start of oscillation until oscillation stabilizes to a
natural frequency (oscillation frequency). Therefore, disable CPU operation immediately after
the start of oscillation, and supply a clock to the CPU when oscillation completely stabilizes
following the elapse of the oscillation stabilization wait time. Specify a oscillation stabilization
wait time suitable for the oscillator used because the time required for oscillation to stabilize
varies depending on the type of oscillator (crystal, ceramic, or other material). The oscillation
stabilization wait time can be selected by defining the clock selection register (CKSCR).
When clock mode is switched from main clock to PLL clock, main clock to subclock, subclock to
main clock, or subclock to PLL clock, the CPU runs in the clock mode set before switching for
the oscillation stabilization wait time. After the oscillation stabilization wait time has elapsed, the
CPU changes to the specified clock mode.
Figure 5.5-1 "Operation immediately after start of oscillation" illustrates operation immediately
after the start of oscillation.
Figure 5.5-1 Operation immediately after start of oscillation
X1
Start of Oscillation Stable Oscillation
Oscillator oscillation stabilization
oscillation time wait time
CHAPTER 5 CLOCKS
Switching to operation start or
changing from PLL clock/sub clock
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