Fig.6.4.7 Wiring For Large Current Signal Line; Fig.6.4.8 Wiring For Signal Line Where Potential Levels Charge Frequently; Fig.6.4.9 Vss Pattern On Underside Of An Oscillator - Renesas 7200 Series User Manual

APPENDIX
6.4 Countermeasures against noise
6.4.4 Oscillator concerns
Take care to prevent an oscillator that generates clocks for a microcomputer operation from being affected
by other signals.
(1) Keeping an 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.
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.
(2) Installing an oscillator away from signal
l i n e s w h e r e p o t e n t i a l l e v e l s c h a n g e
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.
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.
(3) Oscillator protection using V
As for a two-sided printed circuit board, print
a V pattern on the underside (soldering side)
SS
of the position (on the component side) where
an oscillator is mounted.
Connect the V
SS
V pin with the shortest possible wiring.
SS
Besides, separate this V
V patterns.
SS
6-14
pattern
SS
pattern to the microcomputer
pattern from other
SS
7220 Group User's Manual
Mutual inductance
M
Large
current

Fig.6.4.7 Wiring for large current signal line

Do not cross
Fig.6.4.8 Wiring for signal line where potential
levels charge frequently
An example of V
underside of a printed circuit board
Oscillator wiring
pattern example
Separate the V line for oscillation from other V
SS
Fig.6.4.9 V pattern on underside of an oscillator
SS
Microcomputer
X
IN
X
OUT
V
SS
GND
N.G.
CNTR
X
IN
X
OUT
V
SS
patterns on the
SS
X
IN
X
OUT
V
SS
SS
lines