M38203M4 Datasheet, PDF (297/344 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
3.2 Countermeasures against noise
3.2.3 Oscillator concerns
Take care to prevent an oscillator that generates
clocks for a microcomputer operation from being
affected by other signals.
Mutual inductance
M
Microcomputer
(1) Installing an oscillator away from large cur-
rent signal lines
Install a microcomputer (and especially an
oscillator) as far as possible from signal lines
where a current larger than the tolerance of
current value flows.
Large
current
XIN
XOUT
VSS
GND
Fig. 3.2.5 Wiring for a large current signal line
Reason
In the system using a microcomputer, there
are signal lines for controlling motors, LEDs,
and thermal heads or others. When a large
current flows through those signal lines, strong
noise occurs because of mutual inductance.
3.2.4 Installing an oscillator away from signal lines where
potential levels change frequently
Install an oscillator away from signal lines where
potential levels change frequently. Also, do not cross
such signal lines over the clock lines or the signal
lines which are sensitive to noise.
Reason
Signal lines where potential levels change frequently
(such as the CNTR pin signal line) may affect other
lines at signal rising edge or falling edge. If such
lines cross over a clock line, clock waveforms may
be deformed, which causes a microcomputer failure
or a program runaway.
Do not cross
CNTR
XIN
XOUT
VSS
Fig. 3.2.6 Wiring to a signal line where potential
levels change frequently
3820 GROUP USER’S MANUAL
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