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Edge detection instructions
DF
DF is a rising edge differential instruction. The DF instruction executes and turns ON output o for a
Description
singular scan duration if the trigger i changes from an OFF to an ON state.
Availability of DF (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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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 rising edge at the input Increment increments the counter.
LD
ST
When programming with structured text, enter the following:
IF
DF(Increment)
Counter:=Counter+1;
END_IF;
884
Rising 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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Constant
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