SFC elements step and transition

Step symbol: , Transition symbol:

TwinCAT always inserts steps and transitions as a combination. Inserting a step without a transition or a transition without a step results in a compile error. You can change the name by double-clicking on it.

Step names must be unique within the scope of the "father" function block. Keep this in mind when using actions that are also programmed in SFC.

Note that you can make a step an initial step with the Init step command or by setting the corresponding property in the SFC element Properties.

Each step is defined by the step properties, which you can view and edit depending on the options set in the Properties view.

You must add actions that you want to execute when the step is active. There are "IEC actions" and "Step actions“. For details, refer to the Action section for the SFC element.

It is the user's responsibility to assign the desired expression to a transition variable if the transition contains multiple instructions.

Transitions consisting of a transition or property object are indicated by a small triangle in the upper right corner of the transition rectangle.

See also:

• Programming in Sequential Function Chart (SFC)
• Object Transition
• SFC Element Properties
• SFC element Action
• Method call - virtual function call
• TC3 User Interface documentation: Command Insert step transition
• TC3 User Interface documentation: Command Init step