M38263EBFP datasheet(59/91 Pages) RENESAS

59 / 91 page

Rev.1.00

Sep 06, 2006

page 59 of 88

REJ03B0181-0100

3826 Group (One Time PROM version)

(3) Oscillator concerns

In order to obtain the stabilized operation clock on the user system

and its condition, contact the oscillator manufacturer and select

the oscillator and oscillation circuit constants. Be careful espe-

cially when range of voltage or/and temperature is wide.

Also, take care to prevent an oscillator that generates clocks for a

microcomputer operation from being affected by other signals.

➀ Keeping 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 toler-

ance of current value flows.

● Reason

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 oc-

curs because of mutual inductance.

➁ 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.

● 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.

➀ Keeping oscillator away from large current signal lines

➁ Installing oscillator away from signal lines where potential

levels change frequently

Fig. 66 Wiring for a large current signal line/Wiring of signal

lines where potential levels change frequently

XIN

XOUT

VSS

Microcomputer

Mutual inductance

Large

current

GND

XIN

XOUT

VSS

CNTR

Do not cross

N.G.

Fig. 67 Wiring for the VPP pin of One Time PROM

(4) Analog input

The analog input pin is connected to the capacitor of a compara-

tor. Accordingly, sufficient accuracy may not be obtained by the

charge/discharge current at the time of A/D conversion when the

analog signal source of high-impedance is connected to an analog

input pin. In order to obtain the A/D conversion result stabilized

more, please lower the impedance of an analog signal source, or

add the smoothing capacitor to an analog input pin.

(5) Difference of memory type and size

When Mask ROM and PROM version and memory size differ in

one group, actual values such as an electrical characteristics, A-D

conversion accuracy, and the amount of proof of noise incorrect

operation may differ from the ideal values.

When these products are used switching, perform system evalua-

tion for each product of every after confirming product

specification.

(6) Wiring to VPP pin of One Time PROM version and EPROM version

Connect an approximately 5 kΩ resistor to the VPP pin the shortest

possible in series.

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

resistor is used in the Mask ROM version, the microcom-

puter operates correctly.

● Reason

The VPP pin of the 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 built-in PROM. Because of this, noise can en-

ter easily. If noise enters the VPP pin, abnormal instruction codes

or data are read from the built-in PROM, which may cause a pro-

gram runaway.

P70/VPP

VSS

About 5 kΩ

Source signal

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