SFC Element Properties

You can edit the properties of an SFC element in the Properties view. Use the command View > Properties Window to open this view. Which properties are displayed depends on the currently selected element.

SFC Element Properties 1:

Which properties are displayed next to the element in the SFC diagram depends on the TwinCAT options settings in category TwinCAT > PLC Environment > SFC editor, View tab.

General

Property

Value description

Name

Element name, default <element><consecutive number>, e.g. step name "Step0", "Step1", branch name "Branch0", etc.

Comment

Element comment (text), e.g. counter reset. You can insert line breaks with [Ctrl] + [Enter].

Symbol

For each SFC element, TwinCAT creates an implicit variable with the same name as the element.

Specific

Property

Value description

Init step

SFC Element Properties 2:: This option is only enabled for the step that is currently defined as the initial step. By default, this is the first step in an SFC diagram.

If you have activated this property for another step, it must be deactivated for the step that previously had this property, in order to avoid compile errors.

Duplicate or copy

This option is available for steps that contain a step action (entry action, main action or exit action), and for transitions that are linked to a transition object.

SFC Element Properties 3:: When you copy the step/transition, a new object is created for each of the called actions/transitions. It contains a copy of the implementation code of the copied object.

SFC Element Properties 4:: When you copy the step or transition, the link to the relevant object is retained for the associated actions/transitions. No new objects are created. The source and copies of the step or transition call the same action/transition.

Embedded objects are displayed in the PLC project tree with an underscore in the name.

You can use the commands Change duplication > Set and Remove to "embed" all step actions or transitions that are called in an SFC function block or to cancel the embedding.

Times

  • Minimum active
  • Maximum active

Minimum time for which the step is active, even if the subsequent transition is TRUE.

Maximum time for which the step may be active. If the time is exceeded, TwinCAT sets the implicit variable SFCError to TRUE.

Time specifications according to the IEC syntax (e.g. t#8 s) or TIME variable; default: t#0s.

Actions

  • Entry Action
  • Step action
  • Exit action
  • Entry action: TwinCAT executes this action after the step has been activated.
  • Step action: TwinCAT executes this action if the step is active and any entry action has already been executed.
  • Exit action: If the step is deactivated, TwinCAT performs this action in the following cycle.

Note the processing sequence.

SFC Element Properties 5:

You can use the corresponding implicit SFC variables and flags to obtain information about the status of a step or an action, or about timeouts.

See also: