38D2 datasheet(93/136 Pages) RENESAS

93 / 136 page

Rev.3.02

Apr 10, 2008

Page 93 of 131

REJ03B0177-0302

38D2 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 and temperature is wide.

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

microcomputer operation from being affected by other signals.

1. 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

tolerance 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

occurs because of mutual inductance.

2. 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.

Fig. 93 Wiring for a large current signal line/Wiring of

signal lines where potential levels change

frequently

(4) Analog input

The analog input pin is connected to the capacitor of a voltage

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 smoothing capacitor to an

analog input pin.

(5) Difference of memory size

When 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

evaluation for each product of every after confirming product

specification.

XIN

XOUT

VSS

Microcomputer

Mutual inductance

Large

current

GND

XIN

XOUT

VSS

CNTR

Do not cross.

N.G.

1. Keeping oscillator away from large current signal lines

2. Installing oscillator away from signal lines where potential

levels change frequently

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