Datasheet

Table Of Contents
Section 5 Clock Pulse Generator
Rev. 2.00 Jul. 04, 2007 Page 98 of 692
REJ09B0309-0200
(2) Wait Time
After the system clock is generated, the time required for the amplitude of the oscillation
waveform to increase, the oscillation frequency to stabilize, and the CPU and peripheral functions
to begin operating.
Oscillation
waveform
(OSC2)
System clock
(φ)
Oscillation
start time
Operating
mode
Standby mode,
watch mode,
or subactive
mode
Wait time
Oscillation stabilization wait time
Active (high-speed) mode or
active (medium-speed) mode
Interrupt accepted
Figure 5.12 Oscillation Stabilization Wait Time
As the oscillation stabilization wait time required is the same as the oscillation stabilization time
(t
rc
) at power-on, specified in the AC characteristics, set the STS2 to STS0 bits in SYSCR1 to
specify the time longer than the oscillation stabilization time (t
rc
).
Therefore, when a transition is made from standby mode, watch mode, or subactive mode, to
active (high-speed/medium-speed) mode, with an resonator connected to the system clock
oscillator, careful evaluation must be carried out on the mounting circuit before deciding the
oscillation stabilization wait time. For the wait time, secure the time required for the amplitude of
the oscillation waveform to increase and the oscillation frequency to stabilize. In addition, since
the oscillation start time differs according to mounting circuit constants, stray capacitance, and so
forth, suitable constants should be determined in consultation with the resonator manufacturer.
5.5.4 Note on Subclock Stop State
To stop the subclock, a state transition should not be made except to mode in which the system
clock operates. If the state transition is made to other mode, it may result in incorrect operation.