M16C62_M Datasheet, PDF (607/615 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/60 SERIES

Appendix 5
Mitsubishi microcomputers
M16C / 62A Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
1.1.3 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 (within 20 mm) across the grounding lead of a capacitor which is connected to
an oscillator and the VSS pin of a microcomputer as short as possible.
• Separate the VSS pattern only for oscillation from other VSS patterns. (See Figure 1.4.3.)
Noise
XIN
VSS
XOUT
N.G.
Figure 1.1.3. Wiring for clock I/O pins
XIN
VSS
XOUT
O.K.
q 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 VSS level of a microcom-
puter and the VSS level of an oscillator, the correct clock will not be input in the microcomputer.
1.1.4 Wiring to CNVss pin
Connect the CNVss pin to the Vss pin with the shortest possible wiring.
q Reason
The processor mode of a microcomputer is influenced by a potential at the CNVss pin. If a potential differ-
ence is caused by the noise between pins CNVss and Vss, the processor mode may become unstable. This
may cause a microcomputer malfunction or a program runaway.
Noise
CNVSS
VSS
N.G.
Figure 1.1.4. Wiring for CNVss pin
2-290
CNVSS
VSS
O.K.