Page 12 - Introduction to Microcontrollers Architecture, Programming, and Interfacing of The Motorola 68HC12

Preface xi

PREFACE

Programming is an essential engineering skill. To almost any engineer, it is as
important as circuit design to an electrical engineer, as statistics to a civil engineer, and
as heat transfer to a chemical engineer. The engineer has to program in high-level
languages to solve problems. He or she also should be able to read assembly-language
programs to understand what a high-level language does. Finally, he or she should
understand the capabilities of a microcontroller because they are components in many
systems designed, marketed, and maintained by engineers. The first goal of this book
then is to teach engineers how a computer executes instructions. The second goal is to
teach the engineer how a high-level language statement converts to assembler language.
A final goal is to teach the engineer what can be done on a small computer and how the
microcomputer is interfaced to the outside world. Even the nonprogramming engineer
should understand these issues. Although this book is written for engineers, it will serve
equally well for anyone, even hobbyists, interested in these goals.
The reader is taught the principles of assembly-language programming by being
shown how to program a particular microcomputer, the Motorola 6812. The important
thing about the 6812 is that it has a straightforward yet powerful instruction set, midway
between smaller and more powerful microcontrollers; from it the reader can adjust to
these smaller or more powerful microcontrollers. The best way to learn these principles
is to write a lot of programs, debug them, and see them work on a real microcontroller.
This hands-on experience can be inexpensively obtained on the 6812. Several 6812
boards, which do everything described in this book, are available for under $100. (This
price doesn't include the personal computer that hosts the 6812 target system.)
The following discussion outlines the book and explains several decisions that
were made when we wrote the book. Optional chapters are available for readers having
various interests. The main skills taught in each chapter are summarized.
Chapters 1 to 3 discuss programming using hand-translated machine code, and the
implementation of machine instructions in an idealized microcontroller. The assembler is
not introduced until Chapter 4. This gives the engineering student a fine feeling for the
machine and how it works, and helps him or her resolve problems encountered later with
timing in input/output programming or with the use of addressing modes in managing
data structures. Chapter 1 explains how a microprocessor interacts with the memory and
how it executes the instruction cycle. The explanation focuses on a microcomputer and
is simplified to provide just enough background for the remainder of the text. Simple
instructions and elementary programs are introduced next. Pointing out that there is no
best program to solve a problem, Chapter 1 observes what makes a good program and
encourages the reader to appreciate good programming style. A discussion of the
available organizations of 6812 microcontrollers concludes this chapter.
In Chapter 2, the main concept is the alternative forms of the same kind of
instruction on the 6812. Rather than listing the instructions alphabetically, as is
desirable in a reference book, we group together instructions that perform the same type
of function. Our groups are the classical ones, namely, the move, arithmetic, logical,
edit, control, and input/output groups. Although other groupings are also useful, this
one seerns to encourage the student to try alternative instructions as a way of looking for
the best instruction for his or her purpose. The 6812 has an extensive set of addressing
modes that can be used with most instructions; these are covered in Chapter 3, The