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Introduction to IEC 61131-3 programming

Programming languages

DDS-IEC61131 EN 2.0

5.3 Sequential Function Chart (SFC)

(Sequential Function Chart, SFC)

Sequential Function Chart is a graphically oriented language that enables the description of a time

sequence of different actions within a program.

An organization unit written in SFC consists of steps which are linked by means of directed

connections (transitions).

Fig. 3 Example of a network in SFC

The graphical representation of transitions and steps reminds of a flow chart, is easily readable and

perfectly suitable for programming higher level status sequences.

Steps

Steps consist of flags and one or several actions or Boolean variables.

• The actions of steps are separated from the steps and can be used repeatedly in an

organization unit.

• Qualifiers activate and deactivate actions and Boolean variables (sometimes with time delay).

• Concurrences are possible because an action can still be active when the next step is already

being processed, e.g. the qualifier S (set).

Actions

Actions can contain instructions in IL or ST, networks in FBD or LD, or a sequential function (SFC).

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