4518 Datasheet, PDF (69/160 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4518 Group
(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 kΩ or more resistor to XIN pin in series
to limit of current by competitive signal.
M34518
XIN
Open
XOUT
Open
* Do not use the CMCK, CRCK and
CYCK instructions in program.
Fig. 58 Handling of XIN and XOUT when operating on-chip oscillator
XIN
CIN
M34518
Execute the CMCK instruc-
tion in program.
* ^XOUT
Note: Externally connect a damping
resistor Rd depending on the
Rd
oscillation frequency.
(A feedback resistor is built-in.)
Use the resonator manu-
COUT
facturer’s recommended value
because constants such as ca-
pacitance depend on the
resonator.
Fig. 59 Ceramic resonator external circuit
M34518
* Execute the CRCK
instruction in program.
R
XIN
XOUT
Open
C
Fig. 60 External RC oscillation circuit
M34518
* Execute the CYCK instruction
in program.
XIN
CIN
XOUT
Note: Externally connect a damping
Rd
resistor Rd depending on the
oscillation frequency.
(A feedback resistor is built-in.)
COUT
Use the quartz-crystal manu-
facturer’s recommended value
because constants such as ca-
pacitance depend on the
resonator.
Fig. 61 External quartz-crystal circuit
M34518
* Execute the CMCK instruction in
program, and set the main clock
f(XIN) to be enabled (MR1=0)
XIN
XOUT VDD
R
Open _VSS
1kΩ or more
External oscillation circuit
Fig. 62 External clock input circuit
Rev.3.01 2005.06.15 page 69 of 157
REJ03B0008-0301