M38B53M4-059FP datasheet(278/355 Pages) MITSUBISHI

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APPENDIX

38B5 Group User’s Manual

3.4 Countermeasures against noise

(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.

Fig. 3.4.8 Wiring of signal lines where potential levels change frequently

(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. 3.4.9 VSS pattern on the underside of an oscillator

XIN

XOUT

VSS

CNTR

Do not cross

N.G.

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

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