7733 datasheet(615/940 Pages) RENESAS

615 / 940 page

7733 Group User’s Manual

21-67

APPENDIX

4. Oscillator protection

The oscillator, which generates the basic clock for

the microcomputer operations, must be protected

from the affect of other signals.

(1) Distance oscillator from signal lines with

large current flows

q Install the microcomputer, especially the

oscillator, as far as possible from signal lines

which handle currents larger than the

microcomputer current value tolerance.

Reason

The microcomputer is used in systems which

contain signal lines for controlling motors, LEDs,

thermal heads, etc. Noise occurs due to mutual

inductance when a large current flows through

the signal lines.

(2) Distance oscillator from signal lines with

frequent potential level changes

q Install an oscillator and a connecting pattern

away from signal lines in which potential levels

change frequently.

q Do not cross these signal lines over clock-

related or noise-sensitive signal lines.

Reason

Signal lines with frequently changing potential

levels may affect other signal lines at the rising

or falling edge. In particular, if the lines cross

over a clock-related signal line, clock waveforms

may

deformed,

which

causes

microcomputer malfunction or a program

runaway.

Fig. 19 Wiring for signal lines with large current

flows

Fig. 20 Wiring for signal lines with frequent

potential level changes

XIN

XOUT

Vss

M37733MHBXXXFP

Mutual inductance

Large

current

GND

XIN

XOUT

Vss

Do not cross.

g I/O pin for signal with frequently changing

potential levels.

M37733MHBXXXFP

Appendix 8. Countermeasure examples against noise

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