Preface
This book is about the digital logic design of microprocessors. It is intended
to provide both an understanding of the basic principles of digital logic
design, and how these fundamental principles are applied in the building of
complex microprocessor circuits using current technologies. Although the basic
principles of digital logic design have not changed, the design process and
the implementation of the circuits have changed. With the advances in fully
integrated modern-computer-aided design (CAD) tools for logic synthesis,
simulation, and the implementation of circuits in programmable logic devices
(PLDs), such as field programmable gate arrays (FPGAs), it is now possible to
design and implement complex digital circuits very easily and quickly.
Many excellent books on digital logic design have followed the traditional
approach of introducing the basic principles and theories of logic design and
the building of separate combinational and sequential components. However,
students are left to wonder about the purpose of these individual components
and how they are used in the building of microprocessors—the ultimate in
digital circuits. One primary goal of this book is to fill in this gap by
going beyond the logic principles and the building of individual components.
The use of these principles and the individual components are combined
together to create datapaths and control units, and finally, the building of
real, dedicated custom microprocessors and general-purpose microprocessors.
Previous logic design and implementation techniques mainly focus on the
logic-gate level. At this low level, it is difficult to discuss larger and
more complex circuits beyond the standard combinational and sequential
circuits. However, with the introduction of the register-transfer technique
for designing datapaths and the concept of a finite state machine for
control units, we easily can implement an arbitrary algorithm as a dedicated
microprocessor in hardware. The construction of a general-purpose
microprocessor then comes naturally as a generalization of a dedicated
microprocessor.
With the provided CAD tool and the optional FPGA hardware development kit,
students actually can implement these microprocessor circuits and see them
execute, both in software simulation and in hardware. The book contains many
interesting examples with complete circuit schematic diagrams and VHDL codes
for both simulation and implementation in hardware. With the hands-on
exercises, the student will learn not only the principles of digital logic
design but, also in practice, how circuits are implemented using current
technologies.
To actually see your own microprocessor come to life in real hardware is an
exciting experience. Hopefully, this will help the students to not only
remember what they have learned but will also get them interested in the
world of digital circuit design.
Advanced and Historical Topics
Sections that are designated with an asterisk ( * ) are either
advanced topics or topics for a historical perspective. These sections may be
skipped without any loss of continuity in learning how to design a
microprocessor.
Summary Checklist
There is a chapter summary checklist at the end of each
chapter. These checklists provide a quick way for students to evaluate whether
they have understood the materials presented in the chapter. The items in the
checklists are divided into two categories. The first set of items deal with
new concepts, ideas, and definitions, while the second set deals with practical
"how to do something" types.
Design of Circuits using VHDL
Although this book provides coverage on VHDL for all of the
circuits, it can be omitted entirely for the understanding and designing of
digital circuits. For an introductory course in digital logic design, learning
the basic principles is more important than learning how to use a hardware
description language. In fact, instructors may find that students may get lost
in learning the principles while trying to learn the language at the same time.
With this in mind, the VHDL code in the text is totally independent of the
presentation of each topic and may be skipped without any loss of continuity.
On the other hand, by studying the VHDL codes, the student can not only
learn the use of a hardware description language but also learn how digital
circuits can be designed automatically using a synthesizer. This book
provides a basic introduction to VHDL and uses the "learn-by-examples"
approach. In writing VHDL code at the dataflow and behavioral levels, the
student will see the power and usefulness of a state-of-the-art CAD
synthesis tool.
Using this Book
This book can be used in either an introductory or a more advanced course in
digital logic design. For an introductory course with no previous background
in logic, Chapters 1 through 4 are intended to provide the fundamental
concepts in designing combinational circuits, and Chapters 6 through 8 cover
the basic sequential circuits. Chapters 9 through 12 on microprocessor
design can be introduced and covered lightly. For an advanced course, where
students already have an exposure to logic gates and simple digital
circuits, Chapters 1 through 4 will serve as a review. The focus should be
on the register-transfer design of datapaths and control units and the
building of dedicated and general-purpose microprocessors, as covered in
Chapters 9 through 12. A lab component should complement the course where
students can have a hands-on experience in implementing the circuits
presented using the included CAD software and the optional hardware
development kit.
Chapter 1—Designing a Microprocessor gives an
overview of the various components of a microprocessor circuit and the
different abstraction levels in which a circuit can be designed.
Chapter 2—Digital Circuits provides the basic principles and theories for
designing digital logic circuits by introducing the use of truth tables and
Boolean algebra and how the theories get translated into logic gates and
circuit diagrams. A brief introduction to VHDL also is given.
Chapter 3—Combinational Circuits shows how
combinational circuits are analyzed, synthesized and reduced.
Chapter 4—Combinational Components discusses the standard combinational
components that are used as building blocks for larger digital circuits.
These components include the adder, subtractor, arithmetic logic unit,
decoder, encoder, multiplexer, tri-state buffer, comparator, shifter, and
multiplier. In an hierarchical design, these components will be used to
build larger circuits such as the microprocessor.
Chapter 5—Implementation Technologies digresses a little by looking at how
logic gates are implemented at the transistor level and the various
programmable logic devices available for implementing digital circuits.
Chapter 6—Latches and Flip-Flops introduces the basic storage elements:
specifically, the latch and the flip-flop.
Chapter 7—Sequential Circuits shows how sequential circuits in the form of
finite state machines are analyzed and synthesized. This chapter also shows
how the operation of sequential circuits precisely can be described using
state diagrams.
Chapter 8—Sequential Components discusses the standard sequential components
that are used as building blocks for larger digital circuits. These
components include the register, shift register, counter, register file, and
memory. Similar to the combinational components, these sequential components
will be used in an hierarchical fashion to build larger circuits.
Chapter 9—Datapaths introduces the register-transfer design methodology and
shows how an arbitrary algorithm can be performed by a datapath.
Chapter 10—Control Units shows how a finite state machine (introduced in
Chapter 7) is used to control the operations of a datapath so that the
algorithm can be executed automatically.
Chapter 11—Dedicated Microprocessors ties the separate datapath and control
unit together to form one coherent circuit—the custom dedicated
microprocessor. Several complete dedicated microprocessor examples are
provided.
Chapter 12—General-Purpose Microprocessors
continues on from Chapter 11 to
suggest that a general-purpose microprocessor is really a dedicated
microprocessor that is dedicated to only read, decode, and execute
instructions. A simple general-purpose microprocessor is designed and
implemented, and programs written in machine language can be executed on it.
Software and Hardware Packages
The newest student edition of Altera's MAX+plus II CAD software is included
with this book on the accompanying CD-ROM. The optional Altera UP2 hardware
development kit is available from Altera at a special student price. An
order form for the kit can be found on the accompanying CD-ROM.
Source files for all of the circuit drawings and VHDL codes presented in
this book also can be found on the accompanying CD-ROM.
Website for the Book
The website for this book is located at the following URL:
www.lasierra.edu/~ehwang/digitaldesign
The website provides many resources for both faculty and
students.
Enoch O. Hwang
Riverside, California
About the Author
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Enoch Hwang has a Ph.D. in Computer Science from the University of California,
Riverside. He is currently an Associate Professor of Computer Science at La
Sierra University in Southern California and a Lecturer in the Departments of
Electrical Engineering, and Computer Science and Engineering at the University
of California, Riverside, teaching digital logic design.
Even from his childhood days, he has been fascinated with electronic circuits.
In one of his first experiments, he attempted to connect a microphone to the
speaker inside a portable radio through the earphone plug. Instead of hearing
sound from the microphone through the speaker, smoke was seen coming out of
the radio. Thus ended that experiment and his family's only radio. He now
continues on his interest in digital circuits with research in embedded
microprocessor systems, controller automation, power optimization, and
robotics.
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