4571 Datasheet, PDF (60/126 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4571 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
signal 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
converter/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 antenna which feeds noise into the
microcomputer, which causes noise to an analog input pin.
VSS
VSS
N.G.
O.K.
Fig 65. 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 66. Analog signal line and a resistor and a capacitor
Rev.1.02 May 25, 2007 Page 60 of 124
REJ03B0179-0102