TABLE OF CONTENTS 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, as reviewed in the introduction - see Chapter 1, Section 9.
In this chapter we will consider:
The definition of function block types;
Re-use of function blocks using function block instances;
Definition and use of IEC standard function blocks;
A review of some of the example function blocks.
The IEC 1131-3 standard encourages the development of well-structured software that can be designed using either a top-down or bottom-up approach. An important concept that underpins this objective is the use of function blocks.
A function block is a well packaged element of software that can be re-used in different parts of an application or even in different projects. A function block can provide a software solution to a small problem, or to the control of a major unit of plant.
A function block describes the behaviour of data, the data structure and an external interface defined as a set of input and output parameters. An important characteristic is that the input and output parameters can only use data types as defined within the standard.
Function blocks are the basic building blocks of a control system and can have algorithms written in any of the IEC languages as described in earlier chapters. Well designed function blocks should have...
