7721 datasheet(523/577 Pages) RENESAS

523 / 577 page

7721 Group User’s Manual

17–60

APPENDIX

Appendix 8. Countermeasure against noise

(3)

Wiring for CNVss pin

Connect CNVss pin to the Vss pin with the shortest possible wiring.

Reason:

The processor mode of the

microcomputer is influenced by a

potential at the CNVss pin when

the CNVss pin and the Vcc or Vss

pin are connected.

If the noise causes a potential

difference between the CNVss pin

and the Vss or Vcc pin, the

processor mode may become

unstable. This may cause a

microcomputer malfunction or a

program runaway.

Noise

CNVss

Vss

M37721

CNVss

Vss

M37721

Acceptable

Not Acceptable

When connecting th e C NVss and Vcc pins, connect

them in the shortest p ossible distance, also .

Fig. 5 Wiring for CNVss pin

2. Connection of bypass capacitor between Vss and Vcc lines

Connect an approximate 0.1

µF bypass capacitor as follows:

q Connect a bypass capacitor between the Vss and Vcc pins, at equal lengths.

q The wiring connecting the bypass capacitor between the Vss and Vcc pins should be as short as

possible.

q Use thicker wiring for the Vss and Vcc lines than that for the other signal lines.

Fig. 6 Bypass capacitor between Vss and Vcc lines

Bypass capacitor

Vcc

Vss

M37721

Wiring pattern

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