Renesas 4514 - Manual (Page 192)

4513/4514 Group User’s Manual
APPENDIX
3-25
3.4 Notes on noise
(3) Wiring for clock input/output pins
• Make the length of wiring which is connected
to clock I/O pins as short as possible.
• Make the length of wiring across the
grounding lead of a capacitor which is
connected to an oscillator and the V
SS pin
of a microcomputer as short as possible.
• Separate the V SS pattern only for oscillation
from other V SS patterns.
Fig. 3.4.3 Wiring for clock I/O pins
● Reason
If noise enters clock I/O pins, clock
waveforms may be deformed. This may
cause a program failure or program runaway.
Also, if a potential difference is caused by
the noise between the V
SS level of a
microcomputer and the V SS level of an
oscillator, the correct clock will not be input
in the microcomputer.
Fig. 3.4.4 Wiring for CNV SS pin
Noise
X IN
X OUT
V SS
X IN
X OUT
V SS
N.G. O.K.
Noise
CNV SS
V SS
CNV SS
V SS
N.G. O.K.
(4) Wiring to CNV SS pin
Connect the CNV SS pin to the V SS pin with
the shortest possible wiring.
● Reason
The operation mode of a microcomputer is
influenced by a potential at the CNV
SS pin.
If a potential difference is caused by the
noise between pins CNV
SS and V SS , the
operation mode may become unstable. This
may cause a microcomputer malfunction or
a program runaway.