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 61131-2 Requirements and Test Procedures
IEC 61131-3 Data types and programming
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 16.1 IEC 61131-3 Data Types.
Figure 16.1 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.