M38C89MB datasheet(43/55 Pages) RENESAS

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SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS

38C8 Group

(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 especially 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 pos-

sible from signal lines where a current larger than the tolerance of

current value flows.

q 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 occurs

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.

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 wave-

forms 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 lev-

els change frequently

Fig. 44 Wiring for the VPP pin of One Time PROM

Fig. 43 Wiring for a large current signal line/Wiring of signal lines

where potential levels change frequently

XIN

XOUT

VSS

CNTR

Do not cross

N.G.

(4) Analog input

The analog input pin is connected to the capacitor of a comparator.

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 smooth-

ing 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 con-

version accuracy, and the amount of proof of noise incorrect opera-

tion may differ from the ideal values.

When these products are used switching, perform system evaluation

for each product of every after confirming product specification.

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

Connect an approximately 5 k

Ω resistor to the VPP pin the shortest

possible in series.

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 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 cur-

rent for writing flow into the built-in 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.

P40/VPP

VSS

About 5k

Ω

Source signal

XIN

XOUT

VSS

Microcomputer

Mutual inductance

Large

current

GND

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