4509 Datasheet, PDF (68/142 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4509 Group
2. Connection of bypass capacitor across VSS line and VDD line
Connect an approximately 0.1 µF bypass capacitor across the VSS
line and the VDD line as follows:
• Connect a bypass capacitor across the VSS pin and the VDD pin at
equal length.
• Connect a bypass capacitor across the VSS pin and the VDD pin
with the shortest possible wiring.
• Use lines with a larger diameter than other signal lines for VSS line
and VDD line.
• Connect the power source wiring via a bypass capacitor to the VSS
pin and the VDD pin.
VDD
VDD
3. Wiring to analog input pins
• Connect an approximately 100 Ω to 1 kΩ resistor to an analog sig-
nal line which is connected to an analog input pin in series.
Besides, connect the resistor to the microcomputer as close as
possible.
• Connect an approximately 1000 pF capacitor across the Vss pin
and the analog input pin. Besides, connect the capacitor to the Vss
pin as close as possible. Also, connect the capacitor across the
analog input pin and the Vss pin at equal length.
<Reason>
Signals which is input in an analog input pin (such as an A/D con-
verter/comparator 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 an-
tenna which feeds noise into the microcomputer, which causes noise
to an analog input pin.
VSS
VSS
N.G.
O.K.
Fig. 67 Bypass capacitor across the VSS line and the VDD line
Noise
Thermistor
(Note)
Microcomputer
Analog
input pin
N.G.
O.K.
VSS
Note : The resistor is used for dividing
resistance with a thermistor.
Fig. 68 Analog signal line and a resistor and a capacitor
Rev.1.02 2006.12.22 page 68 of 140
REJ03B0147-0102