This book has been written as a user guide and tutorial for the new international standard IEC 1131-3 for programmable logic controllers (PLCs). If you are considering designing or writing control programs using any of the IEC 1131-3 languages for the first time, you are advised to gain an understanding of how programs are structured and can be built up from various software elements; this is reviewed in Chapter 2, 'IEC 1131-3 concepts'. This chapter will also explain how the standard provides a selection of programming languages for developing different parts of a control program. Later chapters give specific details on using each of the IEC 1131-3 languages. The suitability of each language for solving different types of industrial control problems is described along with techniques and examples. Facilities in the IEC 1131-3 and an accompanying standard IEC 1131-5 for communicating with other PLCs and devices are discussed in Chapter 12, 'Communications'.

In this chapter we introduce many of the common programming elements that are used with all of the IEC languages. An understanding of how elements such as variables and data types are used is necessary before it is possible to go on to develop programs using Structured Text or any of the other languages. We will see that IEC 1131-3 provides an extensive range of common elements that can be used both with the textual languages Structured Text (ST) and Instruction List (EL), and with the graphical languages Function Block Diagram (FBD) and Ladder Diagram (LD).

This chapter discusses the function block diagram, the first graphical language of the IEC languages in the set structured text, function block diagram, ladder diagram, instruction list and sequential function chart.

Instruction List is a low level language that can be used to express the behaviour of functions, function blocks and programs, and also actions and transitions in Sequential Function Charts.

This chapter discusses function blocks. The use of function blocks is one of the most important concepts formalised by the IEC 1131-3 standard. Using function blocks in the design of control software has many benefits including improving software quality and productivity.

In this chapter the features of a programming station suitable for developing software for IEC based PLCs are reviewed. As the standard has only recently been published, there are few PLC products on the market today that can offer all the features discussed in this chapter.

This appendix contains a list of keywords used in the IEC languages. To avoid the possibility of having ambiguous language identifiers, the names of the following keywords should be regarded as reserved and not used as identifiers.

The following list is a compilation of frequently asked questions about IEC 1131-3. The reader should be aware that it has been the author's best intention that the answers to these questions are correct. However, in due course, it is possible that changes in new editions of the standard may modify or possibly invalidate some of the answers.