M34551E8-XXXFP_98 Просмотр технического описания (PDF) - MITSUBISHI ELECTRIC
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M34551E8-XXXFP_98 Datasheet PDF : 154 Pages
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APPENDIX
3.4 Notes on noise
3.4.3 Oscillator concerns
Take care to prevent an oscillator that generates
clocks for a microcomputer operation from being
affected by other signals.
(1) Keeping oscillator away from large current
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.
q 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.
Mutual inductance
M
Microcomputer
Large
current
XIN
XOUT
VSS
GND
Fig. 3.4.7 Wiring for a large current signal line
N.G.
Do not cross
CNTR
XIN
XOUT
VSS
Fig. 3.4.8 Wiring to a signal line where potential
levels change frequently
(3) Oscillator protection using VSS pattern
As for a two-sided printed circuit board, print
a VSS pattern on the underside (soldering side)
of the position (on the component side) where
an oscillator is mounted.
Connect the VSS pattern to the microcomputer
VSS pin with the shortest possible wiring.
Besides, separate this VSS pattern from other
VSS patterns.
An example of VSS patterns on the
underside of a printed circuit board
Oscillator wiring
pattern example
XIN
XOUT
VSS
(2) Installing oscillator away from signal lines
where potential levels change frequently
Install an oscillator and a connecting pattern
of 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.
Separate the VSS line for oscillation from other VSS lines
Fig. 3.4.9 VSS pattern on the underside of an
oscillator
q Reason
Signal lines where potential levels change
frequently (such as the CARR 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.
3-16
4551 Group User’s Manual
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