Sequential function chart

Sequential function chart (SFC) is a visual programming language used for programmable logic controllers (PLCs).

Actions associated with steps can be of several types, the most relevant ones being Continuous (N), Set (S), and Reset (R).

An SFC rule states that if two steps have an N action on the same target, the variable must never be reset to 0.

It is also possible to insert LD (Ladder Diagram) actions inside an SFC program (and this is the standard way, for instance, to work on integer variables).

SFC is an inherently parallel programming language in that multiple control flows — Program Organization Units (POUs) in the standard's parlance — can be active at once.