SFC programs are executed sequentially within a target cycle, according to the order defined when entering programs in the hierarchy tree. A parent SFC program is executed before its children. This implies that when a parent starts or stops a child, the corresponding actions in the child program are performed during the same cycle.

Within a chart, all valid transitions are evaluated first, and then actions of active steps are performed. The chart is evaluated from the left to the right and from the top to the bottom.

In case of a divergence, 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.

The initial steps define the initial status of the program when it is started. All top level (main) programs are started when the application starts. Child programs are explicitly started from action blocks within the parent programs.

The evaluation of transitions leads to changes of active steps, according to the following rules:

• A transition is 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.

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