M16C62_M Datasheet, PDF (606/615 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
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.
DIP
SDIP
SOP
QFP
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.
Noise
Reset
circuit
VSS
RESET
VSS
Reset
circuit
VSS
RESET
VSS
N.G.
__________
Figure 1.1.2. Wiring for RESET pin
O.K.
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