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DFN
The DFN instruction executes and turns ON output o for a single scan duration if the trigger i
Description
changes from an ON to an OFF state.
Availability of DFN (see page 1319)
PLC types
Be careful when programming with commands that effect the order in which a
program is carried out, e.g. jump or loop instructions within a sequential
function chart or a function block. The order of the instructions might change
depending on the time when the instruction is carried out or the input value.
Specific basic JUMP and LOOP instructions are:
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-
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-
Data types
Variable
Data type
BOOL
input
BOOL
output
Operands
For
i
o
In this example the function has been programmed in ladder diagram (LD) and structured text (ST).
Example
The same POU header is used for all programming languages.
POU header
All input and output variables used for programming this function have been declared in the POU
header.
Body
Each falling edge at the input Decrement decrements the couter.
LD
ST
When programming with structured text, enter the following:
IF
DFN(Decrement)
Counter:=Counter-1;
END_IF;
Falling edge differential
MC (see page 1007) to MCE (see page 1008)
JP (see page 1009) to LBL (see page 1013)
F19_SJP (see page 1010) to LBL (see page 1013)
LOOP (see page 1012) to LBL (see page 1013)
Relay
X
Y
R
L
-
Y
R
L
THEN
T/C
Register
T
C
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-
-
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-
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-
Edge detection instructions
Constant
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885
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