Designing Embedded Hardware, 2nd Edition

Preface

[Enlightenment] resides as comfortably in the circuits of a digital computer ... as at the top of a mountain or in the petals of a flower.

—Robert M. Pirsig, Zen and the Art of Motorcycle Maintenance

Welcome to the second edition of Designing Embedded Hardware. In these pages, I hope to give you an understanding of the design process for creating computer hardware. Just as there is beauty in well-written software, there is beauty in well-designed hardware. With embedded computers, you get to understand the machine at all levels, at once aware of currents flowing through circuit traces and software executing complex algorithms. In fact, it is not possible to write embedded software without understanding the hardware, nor is it possible to design hardware without understanding software. You become involved with the machine to a degree beyond that which is possible with desktop computers. Best of all, it's a lot of fun.

In selecting chips and designs for this book, I have tried to choose, where possible, parts that are both trivial to use yet exceptionally useful. I have no connection, financial or otherwise, with any of the companies or businesses mentioned in this book, and I receive no benefits from them. Every component or product included in this book is there based on its own merits. You may notice a prevalence of components from certain manufacturers. This simply reflects my personal preference for using their chips, based on my experience. Such companies produce chips that are easy to use, are reliable and robust, have great technical support, and provide thorough and comprehensive technical data. In other words, they meet all the necessary requirements for inclusion in a book for beginners.

When the first edition of Designing Embedded Hardware was published, I deliberately left out software. There were two reasons for this. First, there are many good books already written on C programming, embedded firmware development in C, porting Linux to embedded systems, coding in Python, writing Java software, and so on. (And of course, the best of these are naturally published by O'Reilly.) The second reason is that assembly language, that most basic of programming tools, is so different from processor to processor that it would not have been possible to cover all the instruction sets of the processors in the book, let alone do them justice. However, I have decided to include some software in this edition. I won't even attempt to cover the instructions of each processor in this book. What I will do is show some simple assembly language techniques. While the instructions may be wildly different between architectures, the basic concepts are the same.

Also new to this book is a chapter on the Forth programming language. Forth is a relatively old language that has faded from the forefront of software development, and as such, it's rare to find a book giving the language good coverage. Forth is a very useful tool for embedded system development to which many engineers have yet to be exposed. The language is the basis of the Open Firmware standard and is used by design engineers at Apple, Sun, and many other manufacturers. It's a useful language to know, and it is worth taking the time to learn.

Many of the designs in this book look easy, and they are. They are intended as simple building blocks, allowing you to mix and match to achieve the embedded systems you need. I hope you will find this book useful. Once you've finished reading it, go and build something!

—John Catsoulis

Brisbane, Australia

January 2005

[e-mail]

http://www.embedded.com.au

Organization of This Book

This book is informally divided into four sections. The first covers fundamental concepts and introductory material. The second section gives an overview of assembly language and Forth. From there, we'll look at peripherals and how to add functionality to your embedded systems. Finally, we'll look at a variety of processors widely used in embedded systems, and look at the design process for integrating them into computers.

Chapter 1 gives an overview of computer architectures and explains what constitutes an embedded system. Chapters 2 and 3 explore software with assembly language and Forth.

Chapter 4 provides some background electronics theory and introduces some important concepts. If you're already electronics-savvy, then you can skip on to Chapter 5, where we'll look at providing power for your embedded system. We'll also look at how to protect your embedded computer against electrical interference and other gremlins that can cause it grief. In Chapter 6, you'll see how to physically produce and debug an embedded computer system.

Chapters 7 and 8 cover SPI and I²C, two protocols that allow a wide range of small peripherals to be added to microcontrollers. Chapters 9, 10, and 11 cover serial interfaces. These give our embedded system access to host computers and to external peripherals such as modems. We'll look at RS-232C, RS-422, Infrared communication, and USB.

Networks are covered in Chapter 12, where we'll see how to add a low-cost industrial network (CAN) to our embedded computer. Also in Chapter 12, we learn how to add an Ethernet port to our embedded system, by which we can connect to other computers, servers, and gateways and, through them, to the wider Internet.

In Chapter 13, we'll look at real-world interfacing. We'll see how to convert analog signals into digital values for processing and, conversely, how to convert digital values back into analog voltages. We'll also see how to interface sensors to our embedded system, whereby we can measure temperature, light, pressure, acceleration and magnetic fields. Also in Chapter 13, we'll look at Pulse Width Modulation and motor control. We'll see how to use an embedded computer to control small electric motors.

Chapter 14 begins the microprocessor section of the book, where we'll look at the first of our embedded processor architectures, the Microchip PIC. In subsequent chapters, we'll meet a variety of processors, from tiny standalone, 8-bit microcontrollers to 32-bit, bus-based chips with some computing grunt. While it is not possible to cover every embedded processor (as there are literally many hundreds), the chips chosen are representative of various classes of processor. The skills you learn will be adaptable to whatever processor you choose for your application.