455A Datasheet, PDF (64/148 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

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.
455A
XIN
XOUT VDD
VSS
(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.
External oscillation circuit
Fig 62. External clock input circuit
455A
XCIN
XCOUT
Rd
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.
Fig 63. External quarts-crystal circuit
Rev.1.01 Feb 15, 2008 Page 64 of 146
REJ03B0224-0101