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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:

Data types

Duration literals
Unit Description
d Day
h Hour
m Minute
s Second
ms Millisecond
us Microsecond
ns Nanosecond
STRING escape sequences
Escape sequence Produces
$$ $
$' '
$L linefeed
$N newline
$P page (form feed)
$R return
$T tab
$xx hex value


Variable attributes: RETAIN, CONSTANT, AT


Program organization unit (POU)

Configuration, resources, tasks

Object oriented programming (OOP)


  1. ^ Stevic, Tom (5 May 2017). "A very short history of PLC programming platforms". Control Design. Retrieved 11 September 2021.
  2. ^ "IEC 61131-3:2013". International Electrotechnical Commission (IEC). Retrieved 11 September 2021.
  3. ^ PLCopen: The third edition of IEC 61131-3
  4. ^ "Time Duration Literals (IEC 61131-3)".