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APPENDIX
6.4 Countermeasures against noise
(3) Wiring to CNVss pin
Connect the CNV
shortest possible wiring.
Reason
The processor mode of a microcomputer is
influenced by a potential at the CNV
a potential difference is caused by the noise
between pins CNV
mode may become unstable. This may cause
a microcomputer malfunction or a program
runaway.
(4) Wiring to V
pin of One Time PROM version
PP
and EPROM version
When the V
pin is also used as the CNV
PP
pin
1
Connect an approximately 5 kW resistor to
the V
pin the shortest possible in series and
PP
also to the V
SS
resistor, make the length of wiring between
the V
pin and the V
PP
(refer to "countermeasure example 1 of
Figure 6.4.4")
1 When a microcomputer has the CNV
the V
pin is also used as the CNV
PP
Note: Even when a circuit which included an
approximately 5 kW resistor is used in
the Mask ROM version, the micro-
computer operates correctly.
Reason
The V
pin of the One Time PROM and the
PP
EPROM version is the power source input pin
for the built-in PROM. When programming in
the built-in PROM, the impedance of the V
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
abnormal instruction codes or data are read
from the built-in PROM, which may cause a
program runaway.
6-12
pin to the V
pin with the
SS
SS
SS
and V
, the processor
SS
SS
pin. When not connecting the
pin the shortest possible
SS
7220 Group User's Manual
CNV
pin. If
V
Fig.6.4.3 Wiring for CNV
SS
pin,
SS
pin.
SS
Fig.6.4.4 Wiring for V
PROM and EPROM version
PP
pin,
PP
Noise
CNV
SS
SS
N.G.
pin
SS
Approximately
5kΩ
CNV
/V
SS
PP
V
SS
In the shortest
distance
pin of One Time
PP
SS
V
SS
O.K.
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