m3819 Renesas Electronics Corporation., m3819 Datasheet - Page 190

• Manufacturer Part Number: m3819
• Description: Mitsubishi 8-bit Single-chip Microcomputer 740 Family / 38000 Series
• Manufacturer: Renesas Electronics Corporation.

3. APPENDIX
176
3.2.3 Wiring to analog input pins
Reason
Signals which is input in an analog input pin (such as
an A-D converter input pin) are usually output signals
from sensor. The sensor which detects a change of
event is installed far from the printed circuit board with
a microcomputer, the wiring to an analog input pin is
longer necessarily. This long wiring functions as an
antenna which feeds noise into the microcomputer,
which causes noise to an analog input pin.
If a capacitor between an analog input pin and the V
pin is grounded at a position far away from the V
noise on the GND line may enter a microcomputer
through the capacitor.
3.2.4. Oscillator concerns
Take care to prevent an oscillator that generates clocks
for a microcomputer operation from being affected by
other signals.
(1) Keeping an oscillator away from large current
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 induct-
ance.
(2) Keeping an oscillator away from signal lines
Install an oscillator away from signal lines where poten-
tial 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 line) may affect other lines at
signal rising 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.
Connect an approximately 100
Connect an approximately 1000 pF capacitor across
analog signal line which is connected to an analog
input pin in series. Besides, connect the resistor to
the microcomputer as close as possible.
the V
connect the capacitor to the V
possible.
where potential levels change frequently
signal lines
SS
pin and the analog input pin. Besides,
to 1 k resistor to an
SS
pin as close as
3819 Group USER’S MANUAL
3.2 Countermeasures against noise
SS
pin,
SS
Fig.3.2.6 Wiring for a large current signal line
Fig.3.2.7 Wiring to a signal line where potential levels
Fig.3.2.5 Analog signal line and a resistor and a
Sensor
Mutual inductance
Noise
change frequently
capacitor
Do not cross
current
Large
MITSUBISHI MICROCOMPUTER
M
GND
CNTR
X
X
V
IN
OUT
SS
Microcomputer
X
X
V
3819 Group
IN
OUT
SS
Microcomputer
V
Analog
input pin
SS