38K2 datasheet(295/358 Pages) RENESAS

295 / 358 page

3.3 Countermeasures against noise

Rev.2.00

Oct 15, 2006

page 34 of 99

38K2 Group

REJ09B0338-0200

APPENDIX

(5)

Wiring to VPP pin of Flash memory version

Connect an approximately 5 k

Ω resistor to the VPP pin the shortest possible in series and also to the

VSS pin. 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 flash memory version is the power source input pin for the built-in flash

memory. When programming in the built-in flash memory, the impedance of the VPP pin is low to

allow the electric current for writing flow into the flash memory. Because of this, noise can enter

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

flash memory, which may cause a program runaway.

Fig. 3.3.5 Wiring for the VPP pin of the flash memory version

3.3.2 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 VSS line and VCC line.

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

CNVSS/VPP

VSS

In the shortest

distance

Approximately

Ω

Fig. 3.3.6 Bypass capacitor across the VSS line and the VCC line

VSS

VCC

VSS

VCC

N.G.O.K.

38K2 Datasheet(PDF) 295 Page - Renesas Technology Corp

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