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CHAPTER 3 CPU
3.6.5
Oscillation Stabilization Delay Time
When the system transitions to main-run mode from a state in which the main clock is
stopped (such as at power-on, and in main-stop and subclock modes, etc.), a delay
time is required for oscillation to stabilize before operation starts.
Similarly, a subclock oscillation stabilization wait time is required when exiting the
sub-stop mode, because the subclock oscillator is stopped in that mode.
s Oscillation Stabilization Delay Time
After starting, ceramic, crystal, and other resonators typically require the time between several
milliseconds and several tens of milliseconds to stabilize at their fixed oscillation frequency.
Therefore, operation of the CPU and other functions is disabled when oscillation first starts and
no clock signal is supplied to the CPU and peripheral functions until the oscillation stabilization
delay time has passed and the oscillation has sufficiently stabilized.
The time required for oscillation to stabilize depends on the resonator type (crystal, ceramic,
etc.) connected to the clock generator. Consequently, it is necessary to select an oscillation
stabilization delay time that matches the type of oscillator being used.
Figure 3.6-7 "Operation of Oscillator after Starting Oscillation" shows the operation of an
oscillator after starting oscillation.
Figure 3.6-7 Operation of Oscillator after Starting Oscillation
s Main Clock Oscillation Stabilization Delay Time
When first starting operation in main clock mode after a state in which the main clock oscillator
is stopped, a delay time is required for oscillation to stabilize. This delay time starts when the
timebase timer starts counting up from its cleared state, and ends when the count overflows at
the specified bit.
r Oscillation stabilization delay time during operation
A time length must be selected for the oscillation stabilization delay time when an external
interrupt takes the system from main-stop mode back to main-run mode, or when going from
subclock to main clock mode. One of four possible delay times can be selected, using the
oscillator stabilization delay time select bits of the system clock control register (SYCC: WT1,
WT0).
Resonator oscillation time Oscillation stabilization delay time
Normal operation
(wake-up from stop mode
or reset operation)
Oscillation starts
Oscillation stabilizes