M30620FCAFP datasheet(606/615 Pages) RENESAS

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Appendix 5

Mitsubishi microcomputers

M16C / 62A Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

2-289

DIP

SDIP

SOP

QFP

Appendix 5 Countermeasures against noise

Countermeasures against noise are described below. The following countermeasures are generally effec-

tive as countermeasures against noise, however, it is necessary not only to take measures as follows but to

evaluate before actual use.

1.1 Shortest wiring length

The wiring on a printed circuit board can function as an antenna which feeds noise into the microcomputer.

The shorter the total wiring length (by mm unit), the less the possibility of noise insertion into a microcom-

puter.

1.1.1 Package

Select the smallest possible package to make the total wiring length short.

q Reason

The wiring length depends on a microcomputer package. Use of a small package, for example QFP and

not DIP, makes the total wiring length short to reduce influence of noise.

Figure 1.1.1. Selection of packages

____________

1.1.2 Wiring for RESET pin

____________

Make the length of wiring which is connected to the RESET pin as short as possible. Especially, connect

____________

a capacitor across the RESET pin and the VSS pin or reset IC with the shortest possible wiring (within

20mm).

q Reason

____________

The width of a pulse input into the RESET pin is determined by the timing necessary conditions. If noise

____________

having a shorter pulse width than the standard is input to the RESET pin, the reset is released before the

internal state of the microcomputer is completely initialized. This may cause a program runaway.

__________

Figure 1.1.2. Wiring for RESET pin

RESET

Reset

circuit

Noise

VSS

N.G.

Reset

circuit

VSS

RESET

VSS

O.K.

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