M37544 Datasheet, PDF (35/68 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

7544 Group
Clock Generating Circuit
An oscillation circuit can be formed by connecting a resonator be-
tween XIN and XOUT, and an RC oscillation circuit can be formed
by connecting a resistor and a capacitor.
Use the circuit constants in accordance with the resonator
manufacturer's recommended values.
(1) On-chip oscillator operation
When the MCU operates by the on-chip oscillator for the main
clock, connect XIN pin to VCC and leave XOUT pin open.
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.
(2) Ceramic resonator and quartz-crystal oscillator
When the ceramic resonator and quartz-crystal oscillator is used
for the main clock, connect the ceramic/quartz-crystal oscillator
and the external circuit to pins XIN and XOUT at the shortest dis-
tance. A feedback resistor is built in between pins XIN and XOUT.
(3) RC oscillation
When the RC oscillation is used for the main clock, connect the
XIN pin and XOUT pin to the external circuit of resistor R and the
capacitor C at the shortest distance.
The frequency is affected by a capacitor, a resistor and a micro-
computer.
So, set the constants within the range of the frequency limits.
(4) External clock
When the external signal clock is used for the main clock, connect
the XIN pin to the clock source and leave XOUT pin open.
Note: The clock frequency of the
on-chip oscillator depends
M37544
on the supply voltage and
the operation temperature
range.
XIN
XOUT ^{Be careful that variable fre-}
quencies and obtain the
Open sufficient margin.
Fig. 40 Processing of XIN and XOUT pins at on-chip oscillator opera-
tion
XIN
CIN
M37544
Note: Externally connect a
damping resistor Rd
depending on the oscil-
lation frequency.
(A feedback resistor is
XOUT
built-in.)
Use the resonator
Rd
manufacturer’s recom-
mended value because
COUT
constants such as ca-
pacitance depend on
the resonator.
Fig. 41 External circuit of ceramic resonator and quartz-crystal
oscillator
Note:
Connect the external
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circuit of resistor R
and the capacitor C at
the shortest distance.
The frequency is af-
XIN
XOUT
fected by a capacitor,
a resistor and a micro-
R _computer.
So, set the constants
C _{within the range of the}
frequency limits.
Fig. 42 External circuit of RC oscillation
Rev.1.04 2004.06.08 page 35 of 66
REJ03B0012-0104Z
M37544
XIN
External oscillation
circuit
VCC
VSS
Fig. 43 External clock input circuit
XOUT
Open