7480 Group and 7481 Group User's Manual
1-161
HARDWARE
1.18.4 Oscillator Start-Up Stabilization Time
Oscillation is unstable immediately after oscillation is started in the oscillation circuit which uses a ceramic
resonator. Necessary time for stabilizing oscillation is called an oscillator start-up stabilization time.
The oscillator start-up stabilization time necessitated varies with the structure of the oscillation circuit used.
Consult the manufacturer of the resonator for the oscillator start-up stabilization time.
(1)
Oscillator Start-Up Stabilization Time at Power On
The oscillator start-up stabilizing time of 2048 cycles of the XIN pin input signal is automatically
generated after the system is released from reset by timer 1 in the 7480 Group and 7481 Group
(Note).
Note: Timer 1 goes to ‘FF16’ to select f(XIN)/8 as the count source.
Figure 1.18.4 shows an oscillator start-up stabilization time at power on.
Figure 1.18.4 Oscillator Start-Up Stabilization Time at Power On
(2)
Oscillator Start-Up Stabilization Time after Stop Mode
Oscillation stops in the stop mode. When the CPU returns from the stop mode by reset or accepting
an interrupt request, the oscillator start-up stabilization time of 2048 cycles of the input signal to the
XIN pin is automatically generated by timer 1, as occurs at power on.
1.18.5 Notes on Usage
Pay attention to the following notes when an oscillation circuit is used.
The oscillation circuit is held in the high-speed mode after the system is released from reset.
When a ceramic resonator is connected between the XIN and XOUT pins, consult the manufacturer of the
resonator for the oscillator start-up stabilization time.
When an external clock is input to the XIN pin, use a 50% duty cycle pulse signal as the external clock
input to the XIN pin. At this time, leave the XOUT pin open.
Activate timer 1 and disable the acceptance of a timer 1 interrupt request before the STP instruction is
executed.
2.7 V (Note)
VCC
XIN
RESET pin
2048 cycles of XIN pin input signal
2
s or more
Oscillator start-up stabilization time
Note: At f(XIN) = (2.2 VCC–2) MHz.
Apply 0.32 V or less to the RESET pin at the time that power source voltage passes 2.7 V.
Internal reset
Internal reset released
1.18 Oscillation Circuit