SFC Transitions

Transitions represent a condition that changes the program activity from a step to another.

Note: To change the number of a step, transition or jump, select it and hit Ctrl+ENTER keys.

The transition is marked by a small horizontal line that crosses a link drawn between the two steps:

Each transition is identified by a unique number in the SFC program.

Each transition must be completed with a boolean condition that indicates if the transition can be crossed. The condition is a BOOL expression.

In order to simplify the chart and reduce the number of drawn links, you can specify the activity flag of a step (GSnnn.X) in the condition of the transition.

Transitions define the dynamic behaviour of the SFC chart, according to the following rules:

  • A transition in crossed if:
    - its condition is TRUE
    - and if all steps linked to the top of the transition (before) are active
  • When a transition is crossed:
    - all steps linked to the top of the transition (before) are de-activated
    - all steps linked to the bottom of the transition (after) are activated


It is possible to link a step to several transitions and thus create a divergence. The divergence is represented by a horizontal line. Transitions after the divergence represent several possible changes in the situation of the program.

All conditions are considered as exclusive, according to a "left to right" priority order. It means that a transition is considered as FALSE if at least one of the transitions connected to the same divergence on its left side is TRUE.

Below is an example:

Transition 1 is crossed if:
   step 1 is active
   and Cond1 is TRUE

Transition 2 is crossed if:
   step 1 is active
   and Cond2 is TRUE
   and Cond1 is FALSE

Warning: some run-time systems may not support exclusivity of the transitions within a divergence. Please refer to OEM instructions for further information about SFC support.