7630_03 Datasheet, PDF (189/238 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
3.4 Countermeasures against noise
(3) Wiring for the VPP pin of the One Time PROM version and the EPROM version
Connect an approximately 5 kΩ resistor to the VPP pin the shortest possible in series. When not
connecting the resistor, make the length of wiring for the VPP pin the shortest possible.
Note: Even when a circuit which included an approximately 5 kΩ resistor is used in the Mask ROM
version, the microcomputer operates correctly.
Reason
The VPP pin of the One Time PROM and the
EPROM version 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 easily. If noise enters the VPP pin,
abnormal instruction codes or data are read
from the built-in PROM, which may cause a
program runaway.
Approximately
5kΩ
P11/VPP
7630 group
Fig. 3.4.3 Wiring for the VPP pin of the One Time
PROM and the EPROM version
3.4.2 Connection of a bypass capacitor across
the VSS line and the 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
VSS
VSS
N.G.
O.K.
Fig. 3.4.4 Bypass capacitor across the VSS line
and the VCC line
3.4.3 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.
Noise
Thermistor
(Note)
Microcomputer
Analog
input pin
N.G. O.K. _VSS
Note: The resistor is used for dividing
resistance with a thermistor.
Fig. 3.4.5 Analog signal line and a resistor and a
capacitor
3-18
7630 Group User’s Manual