
3-94
APPENDIX
7540 Group User’s Manual
(5) Wiring to V
PP
pin of One Time PROM version
Connect an approximately 5 k
resistor to the V
PP
pin the shortest possible in series and also to the
V
SS
pin. When not connecting the resistor, make the length of wiring between the V
PP
pin and the
V
SS
pin the shortest possible.
Note:
Even when a circuit which included an approximately 5 k
resistor is used in the Mask ROM
version, the microcomputer operates correctly.
G
Reason
The V
PP
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 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
3.4.2 Connection of bypass capacitor across V
SS
line and V
CC
line
Connect an approximately 0.1
μ
F bypass capacitor across the V
SS
line and the V
CC
line as follows:
Connect a bypass capacitor across the V
SS
pin and the V
CC
pin at equal length.
Connect a bypass capacitor across the V
SS
pin and the V
CC
pin with the shortest possible wiring.
Use lines with a larger diameter than other signal lines for V
SS
line and V
CC
line.
Connect the power source wiring via a bypass capacitor to the V
SS
pin and the V
CC
pin.
Fig. 3.4.6 Bypass capacitor across the V
SS
line and the V
CC
line
3.4 Countermeasures against noise
CNV
SS
/V
PP
V
SS
In the shortest
distance
Approximately
5k
V
SS
V
CC
AA
AA
AA
AA
AA
V
SS
V
CC
AA
AA
AA
AA
AA
N.G.
O.K.