M37544 RENESAS [Renesas Technology Corp], M37544 Datasheet - Page 43

• Manufacturer Part Number: M37544
• Description: SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
• Manufacturer: RENESAS [Renesas Technology Corp]

Rev.1.04
REJ03B0012-0104Z
7544 Group
4. Oscillator concerns
So that the product obtains the stabilized operation clock on the
user system and its condition, contact the resonator manufacturer
and select the resonator and oscillation circuit constants.
Be careful especially when range of voltage and temperature is
wide.
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 lev-
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. 56 Wiring for a large current signal line/Writing of signal
els change frequently
Installing oscillator away from signal lines where potential lev-
els change frequently
Keeping oscillator away from large current signal lines
M u t u a l i n d u c t a n c e
lines where potential levels change frequently
2004.06.08
D o n o t c r o s s
c u r r e n t
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M
G N D
N . G .
M i c r o c o m p u t e r
X
X
V
I N
O U T
S S
C N T R
X
X
V
I N
O U T
S S
Fig. 57 Vss pattern on the underside of an oscillator
(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.
Separate the V
Oscillator wiring
pattern example
SS
An example of V
underside of a printed circuit board
line for oscillation from other V
SS
patterns on the
X
X
V
IN
OUT
SS
SS
lines