4518 datasheet(69/160 Pages) RENESAS

69 / 160 page

Rev.3.01

2005.06.15

page 69 of 157

REJ03B0008-0301

4518 Group

Fig. 62 External clock input circuit

Fig. 61 External quartz-crystal circuit

Note: Externally connect a damping

resistor Rd depending on the

oscillation frequency.

(A feedback resistor is built-in.)

Use the quartz-crystal manu-

facturer’s recommended value

because constants such as ca-

pacitance depend on the

resonator.

Fig. 58 Handling of XIN and XOUT when operating on-chip oscillator

Fig. 59 Ceramic resonator external circuit

Fig. 60 External RC oscillation circuit

Execute the CMCK instruc-

tion in program.

Note: Externally connect a damping

resistor Rd depending on the

oscillation frequency.

(A feedback resistor is built-in.)

Use the resonator manu-

facturer’s recommended value

because constants such as ca-

pacitance depend on the

resonator.

M34518

XIN

XOUT

Do not use the CMCK, CRCK and

CYCK instructions in program.

Open

M34518

XIN

XOUT

CIN

COUT

M34518

XIN

XOUT

Execute the CRCK

instruction in program.

Open

M34518

XIN

XOUT

CIN

COUT

Execute the CYCK instruction

in program.

M34518

XIN

XOUT

External oscillation circuit

VDD

VSS

Ω or more

Open

(2) On-chip oscillator operation

When the MCU operates by the on-chip oscillator as the main clock

(f(XIN)) without using the ceramic resonator, RC oscillator or

quartz-crystal oscillation, leave XIN pin and XOUT pin open (Figure

58).

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.

(3) Ceramic resonator

When the ceramic resonator is used as the main clock (f(XIN)),

connect the ceramic resonator and the external circuit to pins XIN

and XOUT at the shortest distance. Then, execute the CMCK in-

struction. A feedback resistor is built in between pins XIN and XOUT

(Figure 59).

(4) RC oscillation

When the RC oscillation is used as the main clock (f(XIN)), connect

the XIN pin to the external circuit of resistor R and the capacitor C

at the shortest distance and leave XOUT pin open. Then, execute

the CRCK instruction (Figure 60).

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

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

limits.

(5) Quartz-crystal oscillator

When a quartz-crystal oscillator is used as the main clock (f(XIN)),

connect this external circuit and a quartz-crystal oscillator to pins

XIN and XOUT at the shortest distance. Then, execute the CYCK in-

struction. A feedback resistor is built in between pins XIN and XOUT

(Figure 61).

(6) External clock

When the external clock signal for the main clock (f(XIN)) is used,

connect the clock source to XIN pin and XOUT pin open. In program,

after the CMCK instruction is executed, set main clock (f(XIN)) os-

cillation start to be enabled (MR1=0).

For this product, when RAM back-up mode and main clock (f(XIN))

stop (MR1=1), XIN pin is fixed to “H” in order to avoid the through

current by floating of internal logic. The XIN pin is fixed to “H” until

main clock (f(XIN)) oscillation starts to be valid (MR1=0) by the

CMCK instruction from reset state. Accordingly, when an external

clock is used, connect a 1 k

Ω or more resistor to XIN pin in series

to limit of current by competitive signal.

Execute the CMCK instruction in

program, and set the main clock

f(XIN) to be enabled (MR1=0)

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