M30620FCAFP datasheet(607/615 Pages) RENESAS

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Appendix 5

Mitsubishi microcomputers

M16C / 62A Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

2-290

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.)

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.

Figure 1.1.4. Wiring for CNVss pin

Figure 1.1.3. Wiring for clock I/O pins

Noise

XIN

XOUT

VSS

XIN

XOUT

VSS

N.G.

O.K.

Noise

CNVSS

VSS

CNVSS

VSS

N.G.

O.K.

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