FUJITSU Semiconductor Controller MB89950/950A - Manual (Page 69)

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CHAPTER 3 CPU
3.6.3 Oscillation Stabilization Delay Time
When the system goes to run mode from a state in which the main clock is stopped
(such as at power-on, and in stop mode and etc.), a delay time is required for oscillation
to stabilize before starting any operation.
■ 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 3.6-5 "Operation of oscillator after starting oscillation" shows the operation of an oscillator after
starting oscillation.
Figure 3.6-5 Operation of oscillator after starting oscillation
■ 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.
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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 stop mode back to run mode. One of two possible delay times can be selected by mask
option.
Resonator oscillation time Oscillation stabilization delay time
Normal operation
(wake-up from stop mode
or reset operation)
Oscillation starts Oscillation stabilizes