M38048FDHKP datasheet(337/387 Pages) RENESAS

337 / 387 page

3-47

REJ09B0212-0100Z

Rev.1.00

Jan 14, 2005

3804 Group (Spec.H)

APPENDIX

3.4 Countermeasures against noise

3.4.4 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.

Fig. 3.4.6 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 CNTR 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

Fig. 3.4.7 Wiring of signal lines where potential levels change frequently

XIN

XOUT

VSS

CNTR

Do not cross

N.G.

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