3823 Datasheet, PDF (61/76 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

3823 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 espe-
cially when range of votage 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
Mutual inductance
M
Microcomputer
Large
current
XIN
XOUT
VSS
GND
➁ Installing oscillator away from signal lines where potential
levels change frequently
Do not cross
CNTR
XIN
XOUT
VSS
N.G.
Fig. 65 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 evalua-
tion for each product of every after confirming product specification.
(6) Wiring to P40/(VPP) pin
When using P40/(VPP) pin as an input port, connect an approximately
5 kΩ resistor to the P40/(VPP) pin the shortest possible in series.
When not using P40/(VPP) pin, connect the pin the shortest pos-
sible to the GND pattern which is supplied to the Vss pin of the
microcomputer. In addition connecting an approximately 5 kΩ re-
sistor in series to the GND could improve noise immunity. In this
case as well as the above mention, connect the pin the shortest
possible to the GND pattern which is supplied to the Vss pin of the
microcomputer.
● Reason
The P40/(VPP) pin of the QzROM version is the power source input pin
for the built-in QzROM. When programming in the QzROM, the im-
pedance of the VPP pin is low to allow the electric current for writing to
flow into the built-in QzROM. Because of this, noise can enter easily. If
noise enters the P40/(VPP) pin, abnormal instruction codes or data are
read from the QzROM, which may cause a program runaway.
(1) When using P40/(VPP) pin as an input port
The shortest
Approx. 5kΩ
P40/(VPP)
(Note)
(Note)
VSS
(2) When not using P40/(VPP) pin
P40/(VPP) _(Note)
The shortest
Approx. 5kΩ
VSS ^(Note)
The shortest
Note. Shows the microcomputer's pin.
Fig. 66 Wiring for the P40/(VPP) pin
Rev.2.02 Jun 19, 2007 page 61 of 73
REJ03B0146-0202