Lenze DDS v2.0 - Manual (Page 17)

Introduction to IEC 61131-3 programming
Programming languages
15
l
DDS-IEC61131 EN 2.0
Transitions
Transitions are between steps. A step that follows a transition is activated if the transition condition
is TRUE.
The following transition conditions are possible:
•
Boolean variable
•
Boolean address
•
Boolean constant (TRUE)
•
A sequence of instructions with a Boolean result in ST syntax ((i<=100) AND b)
•
A sequence of instructions programmed in any language
Alternative branches
In SFC, two or more branches can be defined as alternative branches.
•
Every alternative branch must start and end with a transition.
•
Alternative branches can contain parallel branches and other alternative branches.
•
An alternative branch starts with a horizontal line (alternative start) and ends with a horizontal
line (alternative end) or a jump.
•
If the step before the alternative start line is active, the first transition of every alternative
branch is evaluated from left to right. The first transition from the left that meets the transition
condition TRUE is opened and all following steps are activated.
Parallel branches
In SFC, two or more branches can be defined as parallel branches.
•
Every parallel branch must start and end with a step.
•
Parallel branches can contain alternative branches or other parallel branches.
•
A parallel branch starts with a double line (parallel start) and ends with a double line (parallel
end) or a jump.
•
If the step before the parallel start line is active and the transition condition after this step is
TRUE
, then the first steps of all parallel branches are activated. These branches are
processed in parallel.
•
The steps after the parallel end line are activated if all steps before are active and the
transition condition of this step is TRUE.
Jumps
A jump is a connection with the step whose name is indicated under the jump symbol.
Jumps are necessary because it is not allowed to create upwards or crossing connections.
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