M38048FDHKP datasheet(338/387 Pages) RENESAS

338 / 387 page

3-48

REJ09B0212-0100Z

Rev.1.00

Jan 14, 2005

3804 Group (Spec.H)

APPENDIX

3.4 Countermeasures against noise

Fig. 3.4.9 Setup for I/O ports

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 port

latch at fixed periods.

• Rewrite data to direction registers and pull-up control registers at fixed periods.

(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

Direction register

Port latch

Data bus

I/O port

pins

Noise

N.G.

O.K.

M38048FDHKP Datenblatt(PDF) 338 Page - Renesas Technology Corp