Appendix 4
Appendix 4-29
32180 Group User's Manual (Rev. 1.0)
SUMMARY OF PRECAUTIONS
(3) Protection against signal lines that are the source of strong noise
Do not use any pin that will probably be subject to strong noise for an adjacent port near the oscillator and
VCNT pins. If the pin can be left unused, set it for input and connect to GND via a resistor, or fix it to output
and leave open. If the pin needs to be used, it is recommended that it be used for input-only.
For protection against a still stronger noise source, set the adjacent port for input and connect to GND via a
resistor, and use those that belong to the same port group as much for input-only as possible. If greater
stability is required, do not use those that belong to the same port group and set them for input and connect
to GND via a resistor. If they need to be used, insert a limiting resistor for protection against noise.
<Reasons>
If the ports or pins adjacent to the oscillator and VCNT pins operate at high speed or are exposed to
strong noise from an external source, noise may affect the oscillator circuit, causing its oscillation to
become instable.
Figure 4.13.9 Example Processing of a Noise-Laden Pin
XIN
XOUT
VCNT
Noise
Fast switching
Adjacent pin/peripheral pin
(set for output)
Oscillator
External noise or
switching noise
Switching noise from an output pin applied directly to the port
Noise
Adjacent pin/peripheral pin
(set for input)
External noise from an input pin applied directly to the port
Appendix 4.13 Precautions about Noise
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