The Digital I/O Handbook

Published by Sealevel Systems
ISBN: 0975999400

Reviewed By Chad Lumsden

Before the days of a PC residing on every desk or workstation, engineers and scientists used to dedicate much of their research and time to understanding and developing digital inputs and outputs. As any student from an electrical or computer engineering background will tell you, the basis of nearly all their work stems from the initial knowledge of digital I/O. Understanding the concepts behind logic principals, Boolean operations, truth tables, logic states, and other such principals are required to fully understand the true magnitude of digital I/O. Nearly every electronic device, embedded microprocessor, programmable logic controller, or form of personal computer has its beginnings rooted within the ideology of digital I/O.

Table 1

In “The Digital I/O Handbook”, whose spiral bound pages stay true to the handbook moniker, the authors set out to help users better understand and implement basic digital input and output circuitry, as stated in the Foreword. This handbook is not the definitive writing on the subject, but rather a very informative, solid, and detailed overview of the principles of digital I/O.

The handbook is divided into six parts: four chapters, an appendix, and a glossary. One aspect that is constant throughout the entire book is the presence of detailed diagrams, drawings, tables, source code, and other examples that follow along with the material. This aspect makes following, and more importantly understanding the content seamless.

Chapter 1 is a basic introduction of digital electronics, and gives the reader an informative explanation of logic operations, such as AND, OR, NAND, and NOR logic gates. These are accompanied by truth tables for each, and their logic states are also explained. Many of the symbols that are used in schematics and circuit diagrams are also covered, which helps the reader begin to associate the written material with the figures that are included. Additionally, the ideas behind positive and negative logic are introduced, along with an explanation of the different aspects of latches.

In chapter 2, the focus is more on the output of a digital signal, and the components that manipulate it. An explanation of drivers and buffers is given, along with a rather detailed description of relays and their interactions with digital signals. Also touched upon is the theory of byte masking, and how it is utilized to manipulate a signal. This chapter also gives us our first introduction to source code, in the form of pseudo code.

Chapter 3 details digital inputs in the form of a larger system of circuits. The introduction describes the basic ideas behind digital inputs into a system. Additional topics such as circuit isolation and voltage monitoring are covered, which sheds some insight into what the actual behavior is of such a circuit, and how it is manipulated. The later part of this chapter focuses mainly on software integration with hardware and circuits, albeit on a very small scale.

Chapter 4 picks up where chapter 3 left off, and details the interfacing of sensors to a computer or system. Many different sensors are explained in detail here, as well as how they interact with a particular system. Several working examples are given, and they are all thoroughly explained in reference to the task they were designed for.

All in all, this 75-page handbook covers the basics of digital I/O in a very useful and practical manner. The included appendix and glossary further clarify that which may not have been covered in the general text, and the book as a whole is a great companion to anybody with working knowledge or a general interest in the field of digital I/O.

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Jon Titus developed one of the first hobbyist computers, the Mark-8, in 1974. He has written books and numerous magazine articles about computers and electronics and is a contributor to several engineering magazines.

Tom O’Hanlan is President and CEO Sealevel Systems, Inc., a leader in industrial I/O technology. He is an industry expert on serial and digital I/O products and applications.