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APPENDIX
Appendix 8. Examples of noise immunity improvement
6. Reinforcement of the power source line
For the Vss and Vcc lines, use thicker wiring than that of other signal lines.
When using a multilayer printed circuit board, the Vss and Vcc patterns must each be one of the middle
layers.
The following is necessary for double-sided printed circuit boards:
On one side, the microcomputer is installed at the center, and the Vss line is looped or meshed around
it. The vacant area is filled with the Vss line.
On the opposite side, the Vcc line is wired the same as the Vss line.
The power source lines of external devices which are connected by bus to the microcomputer must be
connected to the microcomputer's power source lines with the shortest possible wiring.
Reasons: With external devices connected to the microcomputer, the levels of many of the signal lines
(total external address buses: 24 bits) may change simultaneously, causing noise on the power
source line.
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7751 Group User's Manual
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