Filter
Top Products
1 Outline
1.3 Cautions on Creation of Fundamental Programs
21
FXCPU Structured Programming Manual
[Basic & Applied Instruction]
1
Outline
2
Instruction List
3
Configuration of
Instruction
4
How to Read
Explanation of
Instructions
5
Basic Instruction
6
Step Ladder
Instructions
7
Applied Instructions
(Program Flow)
8
Applied Instructions
(Move and
Compare)
9
Applied Instructions
(Arithmetic and
Logical Operation)
10
Applied Instructions
(Rotation and
Shift Operation)
1.3.2 Double output (double coil) operation and countermeasures
This subsection explains the double output (double coil) operation and countermeasures.
1. Operation of double output
When a coil (output variable) is used twice (double coil) in another program block to be executed or in the
same program block, the PLC gives priority to the last coil.
Suppose that the same coil Y003 is used in two positions as
shown in the figure on the right.
For example, suppose that 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".
2. Countermeasures against double output
Double output (double coil) does not cause an illegal input (program 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
using step ladder instructions STL or RET.
When you use the step ladder instruction STL or RET, note that the PLC regards it as double coils if you
program, inside the state, an output coil located outside the RET from another program block or the STL
instruction.
X001
Input processing
X001=ON X002=OFF
First
Y003
X002
Second
Output processing
Y003=OFF Y004=ON
Y003
Y004
Y003
A B
Ignored
C E
D
A B
C E
D
A B
C E
D
M100
M101
Or
Y000
Y000
Y000
M100
M101
Y000