Ladder and Functional Block Programming （梯子和功能块编程）.pdf

C H A P T E R 1 1 Ladder and Functional Block Programming W. Bolton This (and the following) chapter comes from the book Programmable Logic Controllers by W. Bolton, ISBN: 9780750681124. The first edition of the book was published in 1996, which explains why the author commences the preface by saying: “Technological advances in recent years have resulted in the development of the programmable logic controller (PLC) and a consequential revolution of control engineering.” (Don’t worry; the chapter presented here is from the fourth edition in 2006.) The thing is that this is something of a timeless subject, so this book provides a very useful introduction to programmable logic controllers and aims to ease the tasks of practicing engineers coming first into contact with programmable logic controllers. It addresses the problem of different programmable control manufacturers using different nomenclature and program forms by describing the principles involved and illustrating them with examples from a range of manufacturers. To assist the reader to develop the skills necessary to write programs for programmable logic controllers, many worked examples, multi-choice questions and problems are included in the book with answers to all multi-choice questions and problems given at the end of the book. Now, Programmable Logic Controllers is not related to FPGAs per se, so you may be wondering why this chapter is included here. The answer is simple—I personally have almost invariably found that anything I learned came in useful at some stage in my career. In order to facilitate PLCs being used by engineers without any great knowledge of conventional programming languages and techniques, an approach called “l