38C3 datasheet(178/224 Pages) RENESAS

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38C3 Group User’s Manual

3-33

APPENDIX

3.4 Countermeasures against noise

(4)

Wiring to VPP pin of One Time PROM version and EPROM version

Connect an approximately 5 k

Ω resistor to the VPP pin the shortest possible in series. When not

connecting the resistor, make the length of wiring between the VPP pin and the VSS pin the shortest

possible.

Note: Even when a circuit which included an approximately 5 k

Ω resistor is used in the Mask ROM

version, the microcomputer operates correctly.

q Reason

The VPP pin of the One Time PROM and the EPROM version is the power source input pin for

the built-in PROM. When programming in the built-in PROM, the impedance of the VPP pin is low

to allow the electric current for writing flow into the PROM. Because of this, noise can enter easily.

If noise enters the VPP pin, abnormal instruction codes or data are read from the built-in PROM,

which may cause a program runaway.

Fig. 3.4.4 Wiring for the VPP pin of the One Time PROM and the EPROM version

3.4.2 Connection of bypass capacitor across VSS line and VCC line

Connect an approximately 0.1

µF bypass capacitor across the VSS line and the VCC line as follows:

• Connect a bypass capacitor across the VSS pin and the VCC pin at equal length.

• Connect a bypass capacitor across the VSS pin and the VCC pin with the shortest possible wiring.

• Use lines with a larger diameter than other signal lines for V SS line and VCC line.

• Connect the power source wiring via a bypass capacitor to the VSS pin and the VCC pin.

Fig. 3.4.5 Bypass capacitor across the VSS line and the VCC line

P51/VPP

RESET

Approximately

5 k

Ω

VSS

VCC

VSS

VCC

N.G.

O.K.

38C3 Datasheet(PDF) 178 Page - Renesas Technology Corp