Renesas M32R/ECU Series, User Manual

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Appendix 4
Appendix
4-23
32180 Group User's Manual (Rev. 1.0)
SUMMARY OF PRECAUTIONS
Appendix 4.13 Precautions about Noise
The following describes precautions to be taken about noise and corrective measures against noise. The cor-
rective measures described here are theoretically effective for noise, but require that the application system
incorporating those measures be fully evaluated before it can actually be put to use.
Appendix 4.13.1 Reduction of Wiring Length
Wiring on the board may serve as an antenna to draw noise into the microcomputer. Shorter the total wiring
length, the smaller the possibility of drawing noise into the microcomputer.
(1) Wiring of the RESET# pin
Reduce the length of wiring connecting to the RESET# pin. Especially when connecting a capacitor between
the RESET# and VSS pins, make sure it is wired to each pin in the shortest distance possible (within 20 mm).
<Reasons>
Reset is a function to initialize the internal logic of the microcomputer. The width of a pulse applied to the
RESET# pin is important and is therefore specified as part of timing requirements. If a pulse in width
shorter than the specified duration (i.e., noise) is applied to the RESET# pin, the microcomputer will not
be reset for a sufficient duration of time and come out of reset before its internal logic is fully initialized,
causing the program to malfunction.
Figure 4.13.1 Example Wiring of the RESET# Pin
Reset
circuit
VSS
RESET#
VSS
RESET#
VSS
Noise
Reset
circuit
VSS
Long wiring Short wiring
Appendix 4.13 Precautions about Noise