17.2 IEC 61131

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The IEC 1131 standards were developed to be a common and open framework for PLC architecture, agreed to by many standards groups and manufacturers. They were initially approved in 1992, and since then they have been reviewed as the IEC-61131 standards. The main components of the standard are;

IEC 61131-1 Overview

IEC 61131-2 Requirements and Test Procedures

IEC 61131-3 Data types and programming

IEC 61131-4 User Guidelines

IEC 61131-5 Communications

IEC 61131-7 Fuzzy control

This standard is defined loosely enough so that each manufacturer will be able to keep their own look-and-feel, but the core data representations should become similar. The programming models (IEC 61131-3) have the greatest impact on the user.

IL (Instruction List) - This is effectively mnemonic programming

ST (Structured Text) - A BASIC like programming language

LD (Ladder Diagram) - Relay logic diagram based programming

FBD (Function Block Diagram) - A graphical dataflow programming method

SFC (Sequential Function Charts) - A graphical method for structuring programs

Most manufacturers already support most of these models, except Function Block programming. The programming model also describes standard functions and models. Most of the functions in the models are similar to the functions described in this book. The standard data types are shown in Figure 253.

Figure 253 IEC 61131-3 Data Types

Previous chapters have described Ladder Logic (LD) programming in detail, and Sequential Function Chart (SFC) programming briefly. Following chapters will discuss Instruction List (IL), Structured Test (ST) and Function Block Diagram (FBD) programming in greater detail.