7480 datasheet(178/337 Pages) RENESAS

178 / 337 page

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

µs 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

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