7540 datasheet(64/366 Pages) RENESAS

64 / 366 page

1-45

REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

7540 Group

HARDWARE

FUNCTIONAL DESCRIPTION

Fig. 46 External circuit of ceramic resonator

Fig. 47 External circuit of RC oscillation

XIN

COUT

CIN

XOUT

M37540

XIN

XOUT

M37540

Fig. 48 External clock input circuit

XIN

XOUT

External oscillation

circuit

VCC

VSS

Open

M37540

XIN

XOUT

M37540

Open

Fig. 49 Processing of XIN and XOUT pins at on-chip oscillator

operation

Clock Generating Circuit

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

tween XIN and XOUT, and an RC oscillation circuit can be formed

by connecting a resistor and a capacitor.

Use the circuit constants in accordance with the resonator

manufacturer's recommended values.

(1) On-chip oscillator operation

When the MCU operates by the on-chip oscillator for the main

clock, connect XIN pin to VSS and leave XOUT pin open.

The clock frequency of the on-chip oscillator depends on the sup-

ply voltage and the operation temperature range.

Be careful that variable frequencies when designing application

products.

(2) Ceramic resonator

When the ceramic resonator is used for the main clock, connect

the ceramic resonator and the external circuit to pins XIN and

XOUT at the shortest distance. A feedback resistor is built in be-

tween pins XIN and XOUT.

(3) RC oscillation

When the RC oscillation is used for the main clock, connect the

XIN pin and XOUT pin to the external circuit of resistor R and the

capacitor C at the shortest distance.

The frequency is affected by a capacitor, a resistor and a micro-

computer.

So, set the constants within the range of the frequency limits.

(4) External clock

When the external signal clock is used for the main clock, connect

the XIN pin to the clock source and leave XOUT pin open.

Select “ceramic resonance” by setting “0” to the Oscillation mode

selection bit of CPU mode register (address 003B16).

Externally connect a

damping resistor Rd de-

pending

the

oscillation frequency.

(A feedback resistor is

built-in.)

Use

the

resonator

manufacturer’s recom-

mended value because

constants such as ca-

pacitance depend on the

resonator.

Note:

Connect the external

circuit of resistor R

and the capacitor C at

the shortest distance.

The frequency is af-

fected by a capacitor,

a resistor and a micro-

computer.

So, set the constants

within the range of the

frequency limits.

Note:

The clock frequency of the

on-chip oscillator depends

on the supply voltage and

the operation temperature

range.

Be careful that variable fre-

quencies and obtain the

sufficient margin.

Note:

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