Sequential Function Chart (SFC)

This section defines Sequential Function Chart (SFC) elements to structure the internal organization of a PLC POU, written in one of the languages defined in this standard, for the purpose of performing sequential control functions. The definitions in this section are derived from IEC 848, with the changes necessary to convert the representations from a documentation standard to a set of execution control elements for a PLC POU.Since SFC elements require storage of state information, the only program organization units which can be structured using these elements are function blocks and programs.If any part of a POU is partitioned into SFC elements, the entire POU is so partitioned. If no SFC partitioning is given for a POU, the entire POU is considered to be a single action which executes under the control of the invoking entity.SFC elementsThe SFC elements provide a means of partitioning a PLC program organization unit into a set of steps and transitions interconnected by directed links. Associated with each step is a set of actions, and with each transition is associated a transition condition.