Appendix 3
Appendix 3-2
32170/32174 Group User's Manual (Rev. 2.1)
PRECAUTIONS ABOUT NOISE
Appendix 3.1 Precautions about Noise
Reset
circuit
VSS
RESET#
VSS
RESET#
VSS
Noise
Reset
circuit
VSS
Long wiring
Short wiring
Appendix 3.1 Precautions about Noise
The following describes precautions to be taken about noise and corrective measures against
noise. The corrective measures described here are theoretically effective for noise, but require that
the application system with these measures incorporated be fully evaluated before it can actually
be put to use.
Appendix 3.1.1 Reduction of Wiring Length
Wiring on the board may serve as an antenna to draws noise into the microcomputer. Shorter the
total wiring length, the smaller the possibility of drawing noise into the microcomputer.
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(1) Wiring of the RESET pin
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Reduce the length of wiring connecting to the RESET pin. Especially when connecting a
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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 pulse width applied
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to the RESET pin is important and is therefore stipulated as part of timing requirements. If a
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pulse in width shorter than the stipulated 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.
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Figure 3.1.1 Example Wiring of the RESET Pin