IEC 61131-3 is the third part (of 10) of the international standard IEC 61131 for programmable logic controllers.
It was first published in December 1993[1] by the IEC; the current (third) edition was published in February 2013.
[2] Part 3 of IEC 61131 deals with basic software architecture and programming languages of the control program within PLC.
It defines three graphical and two textual programming language standards: Variable attributes: RETAIN, CONSTANT, AT