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
function block diagram
sequential function chart
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 |