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FX
3G
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3U
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3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
6 What to Understand before Programming
6.2 Cautions on Creation of Fundamental Programs
1
In
trodu
ct
ct
ion
2
O
ver
vi
ew
3
In
st
ru
ct
ion
Li
st
4
D
evices
in D
etail
etail
5
Specifi
ed t
he
he
D
evice &
C
onst
ant
ant
6
Bef
ore
ore
Pr
ogr
am
am
m
ing
7
B
asic
In
st
ru
ct
ion
8
FNC0
0-F
0-F
NC0
9
Pr
ogr
am
Flow
am
Flow
9
FN
C
C
10-FN
C
19
Mo
ve
ve
&
Co
mp
are
are
10
FNC2
0-F
0-F
NC2
9
Ar
ith.
&
&
Logic
O
per
ati
ati
on
6.2.2
Double output (double coil) operation and countermeasures
1. Operation of double outputs
When a coil gives double outputs (double coils) in a sequence program, the priority is given to the latter one.
Suppose that the same coil Y003 is used in two positions as shown in
the figure on the right.
For example, suppose the X001 is ON and X002 is OFF.
the figure on the right.
For example, suppose the X001 is ON and X002 is OFF.
In the first coil Y003, the image memory turns ON and the output
Y004 turns ON also because the input X001 is ON.
In the second coil Y003, however, the image memory is set to OFF
because the input X002 is OFF.
Accordingly, the actual output to the outside is "Y003 = OFF, Y004 =
ON".
Y004 turns ON also because the input X001 is ON.
In the second coil Y003, however, the image memory is set to OFF
because the input X002 is OFF.
Accordingly, the actual output to the outside is "Y003 = OFF, Y004 =
ON".
2. Countermeasures against double outputs
Double outputs (double coils) do not cause illegal input (program
error), but the operation is disrupted as described above.
Change the program as shown in the example below.
error), but the operation is disrupted as described above.
Change the program as shown in the example below.
SET, RST or jump instruction can be used instead, or a same output coil can be programmed at each state by step
ladder instructions.
When step ladder instructions are used, if an output coil located in the main routine is also used in a state, it is handled
as a double coil. It is better to avoid such programming.
ladder instructions.
When step ladder instructions are used, if an output coil located in the main routine is also used in a state, it is handled
as a double coil. It is better to avoid such programming.
X001
Input processing
X001 = ON X002 = OFF
Y003
First
Y003
Y004
X002
Y003
Second
Output processing
Y003 = OFF Y004 = ON
A
B
Y000
Ignored
C
Y000
E
D
A
B
Y000
C
E
D
A
B
M100
C
E
D
M101
M100
M101
Y000
or
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