Definition: IEC 61131

A family of programming languages for programmable logic controllers (PLCs). Of the three graphical and two textual languages, ladder logic (see example below) was the first language and widely used. IEC 61131 was previously known as IEC 1131. See PLC.

 Graphical

 ladder logic
 function block diagram
 sequential function chart


 Textual

 structured text
 instruction list

The following example of ladder logic shows how logical AND and OR gates are diagrammed. In this case, x = a AND (b OR c).

   ---[ ]-----|--[ ]--|-----( )---
       a      |   b   |      x
              |       |
              |--[ ]--|
              |   c   |