7751 Datasheet, PDF (520/540 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
Appendix 8. Examples of noise immunity improvement
5. Setup for I/O ports
Setup I/O ports by hardware and software as follows:
<Hardware protection>
q Connect a resistor of 100 ohms or more to an I/O port in series.
<Software protection>
q As for an input port, read data several times for checking whether input levels are equal or not.
q As for an output port, since the output data may reverse because of noise, rewrite data to its port Pi
register periodically.
q Rewrite data to port Pi direction registers periodically.
Data bus
Direction register
Port latch
Noise
Port
Fig. 15. Setup for I/O ports
7751 Group User’s Manual
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