Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

27.1 INTRODUCTION

 

· This graphical language is part of the IEC 1131-3 standard.

 

· A simple example is given below.

 

 

· A list of common mnemonics is given below. These include both the IEC 1131-3 values, and those specific to Allen Bradley controllers.

 

 

· A list of the official IEC 1131-3 mnemonics is given below,

 

 

· Here there are three types of modifiers,

  1. N - negates an input or output
  2. ( - nests an operation and puts it on a stack to be pulled off by )
  3. C - forces a check for the currently evaluated results

 

· This language uses a stack structure, like an HP calculator. When the open brackets are used the operations are pushed on the stack, closed brackets pull them back off.

 

· An example of an instruction language subroutine is given below. This program will examine a BCD input on card I:000, and if it becomes higher than 100 then 2 seconds later output O:001/00 will turn on.