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3.6 Clocks
3.6.3 Oscillation Stabilization Delay Time
As the oscillator that provides the source oscillation is stopped before the power is
turned on or during stop mode, a delay time is required for oscillation to stabilize after
the oscillator restarts operation.
n 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.
The oscillation stabilization delay time is optional. The oscillation stabilization delay time is the
time from when the counter starts counting up from zero until an overflow occurs on the
specified bit.
Products with power-on reset require an oscillation stabilization delay time after a power-on
reset, after an external reset in stop mode, or when the CPU wakes up from stop mode by an
external interrupt.
Products without power-on reset only require an oscillation stabilization delay time when the
CPU wakes up from stop mode by an external interrupt.
Figure 3.6.3 shows the operation of an oscillator after starting oscillation.
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CHAPTER 3 CPU
Resonator oscillation time
Oscillation stabilizes
Oscillation starts
Figure 3.6.3 Operation of an Oscillator after Starting Oscillation
Oscillation stabilization delay time
Normal operation
(wake-up from stop mode
or reset operation)
MB89620 series
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