R8C/20 Group, R8C/21 Group 21. Usage Notes
Rev.2.00 Aug 27, 2008 Page 451 of 458
REJ09B0250-0200
21.9 Notes on Noise
21.9.1 Inserting a Bypass Capacitor between VCC and VSS Pins as a
Countermeasure against Noise and Latch-up
Connect the bypass capacitor (at least 0.1 µF) using the shortest and thickest as possible.
21.9.2 Countermeasures against Noise Error of Port Control Registers
During severe noise testing, mainly power supply system noise, and introduction of external noise, the data of
port related registers may be changed.
As a firmware countermeasure, it is recommended to periodically reset the port registers, port direction
registers and pull-up control registers. However, examine fully before introducing the reset routine as conflicts
may be created between this reset routine and interrupt routines.
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