7480 datasheet(43/98 Pages) RENESAS

43 / 98 page

MITSUBISHI MICROCOMPUTERS

7480/7481 GROUP

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

PRELIMINAR

Notice:

This

is not

a final

specification.

Some

parametric

limits

are

subject

to change.

Clock Generating Circuit

The 7480/7481 group is provided with a built-in oscillation circuit.

An oscillation circuit can be formed by connecting a resonator be-

tween XIN and XOUT. Use the manufacturer's recommended

values for constants such as capacitance, which will differ de-

pending on each resonator. The 7480/7481 group has a built-in

feedback resistor between the XIN and XOUT pins, so an external

resistor can be omitted.

q Frequency Control

(1) High-speed Mode

The frequency applied to the clock input pin XIN divided by 2 is

used as the internal clock

φ. This mode is set after reset release.

(2) Medium-speed Mode

The frequency applied to the clock input pin XIN divided by 8 is

used as the internal clock

φ.

q Oscillation Frequency

(1) Stop Mode

If the STP instruction is executed, the internal clock

φ stops at an

“H” level, and the oscillator stops. At this time, timer 1 is set to

“FF16,” and f(XIN)/8 is forcibly connected to the count source of

timer 1. Accordingly, set the timer 1 interrupt enable bit to the dis-

able status (“0”) before execution of the STP instruction.

When a reset or an external interrupt is accepted, oscillation is re-

started, but the internal clock

φ is supplied to the CPU after timer

1 underflows. This is because when an external resonator is used,

some time is required until a start of oscillation.

(2) Wait Mode

If the WIT instruction is executed, the internal clock

φ stops at an

“H” level. But, the oscillator does not stop. When a reset or inter-

rupt is accepted, the stop status is released. The microcomputer

can execute any instruction immediately, because the oscillator

does not stop.

Fig. 44 External circuit of ceramic resonator

Fig. 45 External clock input circuit

XIN

XOUT

COUT

CIN

XIN

XOUT

External oscillation

circuit

Open

VCC

VSS

Duty ratio 50%

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