7643 datasheet(364/424 Pages) RENESAS

364 / 424 page

7643 Group

REJ09B0133-0200

APPENDIX

3.4 Countermeasure against noise

Rev.2.00

Aug 28, 2006

page 41 of 98

Fig. 3.4.5 Wiring for signal lines where potential levels change frequently

3.4.3 Oscillator concerns

Take care to prevent an oscillator that generates clocks for a microcomputer operation from being

affected by other signals.

(1) Keeping oscillator away from large current signal lines

Install a microcomputer (and especially an oscillator) as far as possible from signal lines where a

current larger than the tolerance of current value flows.

q Reason

In the system using a microcomputer, there are signal lines for controlling motors, LEDs, and

thermal heads or others. When a large current flows through those signal lines, strong noise

occurs because of mutual inductance.

XIN

XOUT

VSS

TOUT

Do not cross

N.G.

Fig. 3.4.4 Wiring for a large current signal line

(2) Installing oscillator away from signal lines where potential levels change frequently

Install an oscillator and a connecting pattern of an oscillator away from signal lines where potential

levels change frequently. Also, do not cross such signal lines over the clock lines or the signal

lines which are sensitive to noise.

q Reason

Signal lines where potential levels change frequently (such as the TOUT pin signal line) may

affect other lines at signal rising edge or falling edge. If such lines cross over a clock line, clock

waveforms may be deformed, which causes a microcomputer failure or a program runaway.

XIN

XOUT

VSS

Microcomputer

Mutual inductance

Large

current

GND

7643 Datasheet(PDF) 364 Page - Renesas Technology Corp