IEC 61131-3

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IEC 61131-3 is the third part of the open international standard IEC 61131, and was first published in December 1993 by the IEC. The current (second) edition was published in 2003.

Part 3 of IEC 61131 deals with programming languages and defines two graphical and two textual PLC programming language standards:

Ladder logic (graphical)
Function block diagram (graphical)
Structured text (textual)
Instruction list (textual)

The standard also defines both graphical and textual sequential function chart elements to organize programs for sequential and parallel control processing.