455A datasheet(64/148 Pages) RENESAS

64 / 148 page

Rev.1.01

Feb 15, 2008

Page 64 of 146

REJ03B0224-0101

455A Group

(4) External clock

When the external clock signal is used as the main clock

(f(XIN)), connect the XIN pin to the clock source and leave XOUT

pin open (Figure 62).

Be careful that the maximum value of the oscillation frequency

when using the external clock differs from the value when using

the ceramic resonator (refer to the recommended operating

condition). Also, note that the power down mode (POF and

POF2 instructions) cannot be used when using the external clock.

(5) Sub-clock generating circuit f(XCIN)

Sub-clock signal f(XCIN) is obtained by externally connecting a

quartz-crystal oscillator. Connect this external circuit and a

quartz-crystal oscillator to pins XCIN and XCOUT at the shortest

distance. A feedback resistor is built in between pins XCIN and

XCOUT (Figure 63). XCIN pin and XCOUT pin are also used as

ports D6 and D7, respectively. The sub-clock oscillation circuit is

invalid and the function of ports D6 and D7 are valid by setting

bit 2 of register RG to “1”.

When sub-clock, ports D6 and D7 are not used, connect XCIN/D6

to VSS and leave XCOUT/D7 open.

Fig 62. External clock input circuit

Fig 63. External quarts-crystal circuit

455A

XIN

XOUT

External oscillation circuit

VDD

VSS

455A

XCIN

XCOUT

CIN

COUT

Note: Externally connect a damping resistor Rd

depending on the oscillation frequency.

(A feedback resistor is built-in.)

Use the quartz-crystal manufacturer’s

recommended value because constants such as

capacitance depend on the resonator.

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