7477 datasheet(287/354 Pages) RENESAS

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7470/7471/7477/7478 GROUP USER’S MANUAL

2-52

APPLICATION

2.9 Countermeasures against noise

7470

7471

7477

7478

2.9.4 Consideration for oscillator

Take care to prevent an oscillator that generates clocks

for a microcomputer operation from being affected by other

signals.

(1) Keeping an 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.

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.

(2) Keeping an oscillator away from signal lines where

potential levels change frequently

Install an oscillator and a connecting pattern of an

osillator 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.

Signal lines where potential levels change frequently

(such as the CNTR pin line) may affect other lines at

signal rising 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.

Fig. 2.9.7 Wiring to a signal line where

potential

levels

change

frequently

Fig. 2.9.6 Wiring for a large current signal

line

XIN

XOUT

VSS

Microcomputer

Mutual inductance

Large

current

GND

XIN

XOUT

VSS

CNTR

Do not cross

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