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Appendix 3
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.
(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 connected to each pin with the
shortest possible wiring (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
noise in pulse width shorter than the stipulated duration is applied to the RESET pin, reset will
be negated before the internal logic of the microcomputer is fully initialized, causing the
program to go wild.
Reset
circuit
VSS
Figure 3.1.1 Wiring of the RESET Pin
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Noise
RESET
VSS
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Appendix 3-2
PRECAUTIONS ABOUT NOISE
Appendix 3.1 Precautions about Noise
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Reset
circuit
VSS
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RESET
VSS
Ver.0.10
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