32186 datasheet(1024/1032 Pages) RENESAS

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SUMMARY OF PRECAUTIONS

Appendix 4

Appendix 4-34

32185/32186 Group Hardware Manual

Rev.1.10 REJ09B0235-0110 May 15, 07

Appendix 4.16 Notes on Noise

Appendix 4.16.3 Processing Analog Input Pin Wiring

Insert a resistor of about 100 to 500

Ω in series to the analog signal line connecting to the analog input pin at a

position as close to the microcomputer as possible. Also, insert a capacitor of about 100 pF between the analog

input pin and AVSS pin at a position as close to the AVSS pin as possible.

The signal fed into the analog input pin (e.g., A/D converter input pin) normally is an output signal from a

sensor. In many cases, a sensor to detect changes of event is located apart from the board on which the

microcomputer is mounted, so that wiring to the analog input pin is inevitably long. Because a long wiring

serves as an antenna which draws noise into the microcomputer, the signal fed into the analog input pin

tends to be noise-ridden. Furthermore, if the capacitor connected between the analog input pin and AVSS

pin is grounded at a position apart from the AVSS pin, noise riding on the ground line may penetrate into

the microcomputer via the capacitor.

Appendix Figure 4.16.5 Example of a Resistor and Capacitor Inserted for the Analog Signal Line

Appendix 4.16.2 Inserting a Bypass Capacitor between VSS and VCC Lines

Insert a bypass capacitor of about 0.1 µF between the VSS and VCC lines. At this time, make sure the require-

ments described below are met.

• The wiring length between the VSS pin and bypass capacitor and that between the VCC pin and bypass

capacitor are the same.

• The wiring length between the VSS pin and bypass capacitor and that between the VCC pin and bypass

capacitor are the shortest distance possible.

• The VSS and VCC lines have a greater wiring width than that of all other signal lines.

Appendix Figure 4.16.4 Example of a Bypass Capacitor Inserted between VSS and VCC Lines

VSS

VCC

Chip

VSS

VCC

VSS

VCC

Analog

input pin

AVSS

Sensor

Noise

Microcomputer

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