4524_M Datasheet, PDF (252/310 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 720 FAMILY / 4500 SERIES

4524 Group
APPLICATION
2.10 Oscillation circuit
(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 instruction. A feedback
resistor is built in between pins XIN and XOUT
(Figure 2.10.3).
(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
2.10.4).
The frequency is affected by a capacitor, a
resistor and a microcomputer.
So, set the constants within the range of the
frequency limits.
M34524
Execute the CMCK instruction in
program.
XIN
CI N
Note: Externally connect a damping
XOUT
resistor Rd depending on the
oscillation frequency.
Rd
(A feedback resistor is built-in.)
Use the resonator manufacturer’s
COUT
recommended value because
constants such as capacitance
depend on the resonator.
Fig. 2.10.3 Ceramic resonator external circuit
M34524
* ^{Execute the CRCK}
R
XIN
XOUT
instruction in program.
C
(5) 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. Then,
execute the CMCK instruction (Figure 2.10.5).
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 section “3.1
Electrical characteristics”).
Also, note that the power down function (POF
or POF2 instruction) cannot be used when
using the external clock.
(6) Sub-clock generating circuit f(XCIN)
The quartz-crystal oscillator can be used for
the sub-clock f(XCIN). Connect a quartz-crystal
oscillator and this external circuit to pins XCIN
and XCOUT at the shortest distance. A feedback
resistor is built in between pins XCIN and XCOUT
(Figure 2.10.6).
Fig. 2.10.4 External RC oscillation circuit
M34524
* Execute the CMCK
instruction in program.
XIN
XOUT ^VDD
VSS
External oscillation circuit
Fig. 2.10.5 External clock input circuit
M34524
Note: Externally connect a damping
resistor Rd depending on the
XC IN
XCOUT
oscillation frequency.
(A feedback resistor is built-in.)
Use the quartz-crystal
Rd
manufacturer’s recommended
value because constants such
as capacitance depend on the
CI N
COUT ^resonator.
Fig. 2.10.6 External quartz-crystal circuit
Rev.2.00 Aug, 06 2004
REJ09B0107-0200Z
2-88