Renesas 4514 - Manual (Page 193)

3-26
APPENDIX
3.4 Notes on noise
4513/4514 Group User’s Manual
(5) Wiring to V PP pin of One Time PROM version
In the built-in PROM version of the 4513/4514
Group, the CNV SS pin is also used as the
built-in PROM power supply input pin V PP .
● When the V PP pin is also used as the
CNV SS pin
Connect an approximately 5 k
Ω
resistor to
the V PP pin the shortest possible in series
a n d a l s o t o t h e V S S p i n . W h e n n o t
connecting the resistor, make the length of
wiring between the V
PP pin and the V SS
pin the shortest possible (refer to Figure
3.4.5)
Note: Even when a circuit which included an
approximately 5 k
Ω
resistor is used in the
Mask ROM version, the microcomputer
operates correctly.
● Reason
The V PP pin of the One Time PROM ver-
sion is the power source input pin for the
built-in PROM. When programming in the
built-in PROM, the impedance of the V
PP
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 V
PP pin, abnormal instruction codes or
data are read from the built-in PROM, which
may cause a program runaway.
Fig. 3.4.5 Wiring for the V PP pin of the One Time
PROM version
CNV SS /V PP
When the V PP pin is also used as the CNV SS pin
V SS
In the shortest
distance
Approximately
5k
Ω
3.4.2 Connection of bypass capacitor across V SS
line and V DD line
Connect an approximately 0.1
µ
F bypass capacitor
across the V SS line and the V DD line as follows:
• Connect a bypass capacitor across the V SS pin
and the V DD pin at equal length.
• Connect a bypass capacitor across the V SS pin
and the V DD pin with the shortest possible wiring.
• Use lines with a larger diameter than other signal
lines for V SS line and V DD line.
• Connect the power source wiring via a bypass
capacitor to the V SS pin and the V DD pin.
Fig. 3.4.6 Bypass capacitor across the V SS line
and the V DD line
V
SS
V DD
V SS
V
DD
N.G. O.K.