7630 datasheet(191/238 Pages) RENESAS

191 / 238 page

7630 Group User’s Manual

3-20

APPENDIX

3.4 Countermeasures against noise

3.4.5 Setup for I/O ports

Setup I/O ports using hardware and software as

follows:

• Connect a resistor of 100

Ω or more to an I/O

port in series.

• As for an input port, read data several times by

a program for checking whether input levels are

equal or not.

• As for an output port, since the output data may

reverse because of noise, rewrite data to its data

• Rewrite data to direction registers and pull-up

control registers (only the product having it) at

fixed periods.

When a direction register is set for input port again

at fixed periods, a several-nanosecond short pulse

may be output from this port. If this is undesirable,

connect a capacitor to this port to remove the noise

pulse.

Fig. 3.4.9

Setup for I/O ports

Direction register

Port latch

Data bus

I/O port

pins

Noise

N.G.

O.K.

(3) Oscillator protection using VSS pattern

As for a two-sided printed circuit board, print a

VSS pattern on the underside (soldering side)

of the position (on the component side) where

an oscillator is mounted.

Connect the VSS pattern to the microcomputer

VSS pin with the shortest possible wiring.

Besides, separate this VSS pattern from other

VSS patterns.

Fig. 3.4.8 VSS pattern on the underside of an

oscillator

XIN

XOUT

VSS

An example of VSS patterns on the

underside of a printed circuit board

Oscillator wiring

pattern example

Separate the VSS line for oscillation from other VSS lines

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