Appendix 8. Examples Of Noise Immunity Improvement - Renesas 7700 FAMILY User Manual

Appendix 8. Examples of noise immunity improvement

Generally effective examples of noise immunity improvements are described below. Although the effect of
these countermeasure depends on each system, refer to the following when an noise-related problem
occurs.
1. Short wiring length
The wiring on a printed circuit board may function as an antenna which feeds noise into the microcomputer.
The shorter the total wiring length (by mm unit), the less possibility of noise insertion into the microcomputer.
______
(1) Wiring for
RESET
Make the length of wiring connected to RESET pin as short as possible.
In particular, connect a capacitor between RESET pin and Vss pin with the shortest possible wiring
(within 20 mm).
Reason: If noise is input to RESET pin,
the microcomputer restarts operat-
ion before the internal state of the
m i c r o c o m p u t e r i s c o m p l e t e l y
initialized. This may cause a
program runaway.
Appendix 8. Examples of noise immunity improvement
pin
______
7751 Group User's Manual
______
______
Reset
circuit
Vss
Fig. 5. Wiring for
APPENDIX
M37751
Noise
RESET
Vss
Not
acceptable
M37751
Reset
RESET
circuit
Vss Vss
Acceptable
______
pin
RESET
20–61