On the execution of discrete event systems as sequential function charts

The transition between the supervisory control theory (SCT) and its implementation in programmable logic controllers (PLCs) is not straightforward. This is mainly due to the fact that the SCT is stated in an event based asynchronous setting whilst PLCs are signal based and synchronous. Based on Petri nets the PLC programming language, the sequential function chart (SFC), is an ideal choice for this transition. However, the transition requires detailed knowledge of how the PLC and SFCs work. We present different execution models for SFCs and compare them with the international standard IEC 1131-3.