
Rev.2.00
REJ03B0202-0200
Mar 05, 2007
Page 56 of 70
7549 Group
PRELIMINARY
Notice: This is not a final specification.
Some parametric limits are subject to change.
4. Oscillator concerns
Take care to prevent an oscillator that generates clocks for a mi-
crocomputer 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 toler-
ance 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 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.
<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 wave-
forms may be deformed, which causes a microcomputer failure
or a program runaway.
Fig 75.
Wiring for a large current signal line/Writing of signal
lines where potential levels change frequently
(3) Oscillator protection using V
SS
pattern
As for a two-sided printed circuit board, print a V
SS
pattern on
the underside (soldering side) of the position (on the component
side) where an oscillator is mounted.
Connect the V
SS
pattern to the microcomputer V
SS
pin with the
shortest possible wiring. Besides, separate this V
SS
pattern from
other V
SS
patterns.
Fig 76. V
SS
pattern on the underside of an oscillator
X
IN
X
OUT
V
SS
M
Microcomputer
Mutual inductance
Large
current
GND
X
IN
X
OUT
V
SS
CNTR
Do not cross
N.G.
(1) Keeping oscillator away from large current
signal lines
(2) Installing oscillator away from signal lines
where potential levels change frequently
Oscillator wiring
pattern example
An example of V
SS
patterns on the
underside of a printed circuit board
Separate the V
SS
line for oscillation from other V
SS
lines
X
IN
X
OUT
V
SS