4501 datasheet(206/212 Pages) RENESAS

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3.4 Notes on noise

3-37

4501 Group

APPENDIX

Rev.2.01

Feb 07, 2005

REJ09B0192-0201

(5) Wiring to VPP pin of built-in PROM version

In the built-in PROM version of the 4501 Group,

the CNVSS pin is also used as the built-in

PROM power supply input pin VPP.

q When the VPP pin is also used as the

CNVSS pin

Connect an approximately 5 k

Ω resistor to

the VPP pin the shortest possible in series

and also to the V SS pin. When not

connecting the resistor, make the length of

wiring between the VPP pin and the VSS

pin the shortest possible (refer to Figure

3.4.5)

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 built-in PROM 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. 3.4.5 Wiring for the VPP pin of the built-in

PROM version

CNVSS/VPP

When the VPP pin is also used as the CNVSS pin

VSS

In the shortest

distance

Approximately

Ω

3.4.2 Connection of bypass capacitor across VSS

line and VDD line

Connect an approximately 0.1

µF bypass capacitor

across the VSS line and the VDD line as follows:

• Connect a bypass capacitor across the VSS pin

and the VDD pin at equal length.

• Connect a bypass capacitor across the VSS pin

and the VDD pin with the shortest possible wiring.

• Use lines with a larger diameter than other signal

lines for VSS line and VDD line.

• Connect the power source wiring via a bypass

capacitor to the VSS pin and the VDD pin.

Fig. 3.4.6 Bypass capacitor across the VSS line

and the VDD line

VSS

VDD

VSS

VDD

N.G.

O.K.

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