TABLE OF CONTENTS In this chapter we will review Instruction List; this is the fourth 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.
In this chapter we will review:
The basic structure of the Instruction List language;
The behaviour of standard operators;
How to control the flow of program execution using conditional operators, jumps and labels;
How to call function blocks and functions in IL;
Guidelines on writing IL;
Restrictions on the portability of code between IL and the other IEC languages.
Instruction List is a low level language which has a structure similar to a simple machine assembler. The IEC has developed Instruction List by reviewing the many low level languages offered by a wide range of PLC manufacturers. The IL language, as defined in IEC 1131-3, provides a range of operators that represent those most commonly found in proprietary instruction list languages of current day PLCs.
The basic structure of Instruction List is very simple and easy to learn. It is ideal for solving small straightforward problems where there are few decision points and where there are a limited number of changes in program execution flow.
A number of the manufacturers offering IEC 1131-3 based PLCs have chosen to support ILin preference to...
