M37544 Datasheet, PDF (42/68 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

7544 Group
(5) Wiring to VPP pin of One Time PROM version
Connect an approximately 5 kΩ resistor to the VPP pin the shortest
possible in series and also to the Vss pin. When not connecting
the resistor, make the length of wiring between the VPP pin and
the Vss pin the shortest possible.
Note: Even when a circuit which included an approximately 5 kΩ
resistor is used in the Mask ROM version, the microcom-
puter operates correctly.
<Reason>
The VPP pin of the One Time PROM is the power source input pin
for the built-in PROM. When programming in the built-in PROM,
the impedance of the VPP pin is low to allow the electric current for
writing flow into the PROM. Because of this, noise can enter eas-
ily. If noise enters the VPP pin, abnormal instruction codes or data
are read from the built-in PROM, which may cause a program run-
away.
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 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 func-
tions as an antenna which feeds noise into the microcomputer,
which causes noise to an analog input pin.
CNVSS/VPP
VSS
About 5kΩ
shortest
distance
Noise
Thermistor
(Note)
Microcomputer
Analog
input pin
Fig. 53 Wiring for the VPP pin of the One Time PROM
2. Connection of bypass capacitor across VSS line and VCC line
Connect an approximately 0.1 µF bypass capacitor across the VSS
line and the VCC line as follows:
• Connect a bypass capacitor across the VSS pin and the VCC pin
at equal length.
• Connect a bypass capacitor across the VSS pin and the VCC pin
with the shortest possible wiring.
• Use lines with a larger diameter than other signal lines for VSS
line and VCC line.
• Connect the power source wiring via a bypass capacitor to the
VSS pin and the VCC pin.
VCC
VCC
N.G.
O.K.
VSS
Note : The resistor is used for dividing
resistance with a thermistor.
Fig. 55 Analog signal line and a resistor and a capacitor
• The analog input pin is connected to the capacitor of a voltage
comparator. Accordingly, sufficient accuracy may not be ob-
tained 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 con-
version result stabilized more, please lower the impedance of an
analog signal source, or add the smoothing capacitor to an ana-
log input pin.
VSS
VSS
N.G.
O.K.
Fig. 54 Bypass capacitor across the VSS line and the VCC line
Rev.1.04 2004.06.08 page 42 of 66
REJ03B0012-0104Z