Circuit Design With VHDL

with VHDL

Volnei A. Pedroni

Circuit Design

Circuit Design with VHDL

Volnei A. Pedroni

This textbook teaches VHDL using system examples com￾bined with programmable logic and supported by laboratory

exercises. While other textbooks concentrate only on lan￾guage features, Circuit Design with VHDL offers a fully inte￾grated presentation of VHDL and design concepts by

including a large number of complete design examples,

illustrative circuit diagrams, a review of fundamental design

concepts, fully explained solutions, and simulation results.

The text presents the information concisely yet completely,

discussing in detail all indispensable features of the VHDL

synthesis. The book is organized in a clear progression, with

the first part covering the circuit level, treating foundations

of VHDL and fundamental coding, while the second part cov￾ers the system level (units that might be located in a library

for code sharing, reuse, and partitioning), expanding upon

the earlier chapters to discuss system coding.

Part I, “Circuit Design,” examines in detail the back￾ground and coding techniques of VHDL, including code

structure, data types, operators and attributes, concurrent

and sequential statements and code, objects (signals, vari￾ables, and constants), design of finite state machines, and

examples of additional circuit designs. Part II, “System

Design,” builds on the material already presented, adding

elements intended mainly for library allocation; it examines

packages and components, functions and procedures, and

additional examples of system design. Appendixes on pro￾grammable logic devices (PLDs/FPGAs) and synthesis tools

follow Part II. The book’s highly original approach of teach￾ing through extensive system examples, as well as its

unique integration of VHDL and design, makes it suitable

both for use by students in computer science and electrical

engineering.

Volnei A. Pedroni earned his Ph.D. in electrical engineering

from Caltech. He is currently Professor of Electrical

Engineering at CEFET-PR (Federal Center of Technological

Education of Parana), Brazil.

The MIT Press

Massachusetts Institute of Technology

Cambridge, Massachusetts 02142

http://mitpress.mit.edu

0-262-16224-5

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Circuit Design with VHDL

Pedroni

46183Pedroninew 2004-10-11 14:06 Page 1

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Circuit Design with VHDL

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Circuit Design with VHDL

Volnei A. Pedroni

MIT Press

Cambridge, Massachusetts

London, England

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6 2004 Massachusetts Institute of Technology

All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical

means (including photocopying, recording, or information storage and retrieval) without permission in

writing from the publisher.

This book was set in Times New Roman on 3B2 by Asco Typesetters, Hong Kong and was printed and

bound in the United States of America.

Library of Congress Cataloging-in-Publication Data

Pedroni, Volnei A.

Circuit design with VHDL/Volnei A. Pedroni.

p. cm.

Includes bibliographical references and index.

ISBN 0-262-16224-5 (alk. paper)

1. VHDL (Computer hardware description language) 2. Electronic circuit design.

3. System design. I. Title.

TK7885.7.P43 2004

621.390

5—dc22 2004040174

10 987654321

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To Claudia, Patricia, Bruno, and Ricardo

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Contents

Preface xi

I CIRCUIT DESIGN 1

1 Introduction 3

1.1 About VHDL 3

1.2 Design Flow 3

1.3 EDA Tools 4

1.4 Translation of VHDL Code into a Circuit 5

1.5 Design Examples 8

2 Code Structure 13

2.1 Fundamental VHDL Units 13

2.2 LIBRARY Declarations 13

2.3 ENTITY 15

2.4 ARCHITECTURE 17

2.5 Introductory Examples 17

2.6 Problems 22

3 Data Types 25

3.1 Pre-Defined Data Types 25

3.2 User-Defined Data Types 28

3.3 Subtypes 29

3.4 Arrays 30

3.5 Port Array 33

3.6 Records 35

3.7 Signed and Unsigned Data Types 35

3.8 Data Conversion 37

3.9 Summary 38

3.10 Additional Examples 38

3.11 Problems 43

4 Operators and Attributes 47

4.1 Operators 47

4.2 Attributes 50

4.3 User-Defined Attributes 52

4.4 Operator Overloading 53

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4.5 GENERIC 54

4.6 Examples 55

4.7 Summary 60

4.8 Problems 61

5 Concurrent Code 65

5.1 Concurrent versus Sequential 65

5.2 Using Operators 67

5.3 WHEN (Simple and Selected) 69

5.4 GENERATE 78

5.5 BLOCK 81

5.6 Problems 84

6 Sequential Code 91

6.1 PROCESS 91

6.2 Signals and Variables 93

6.3 IF 94

6.4 WAIT 97

6.5 CASE 100

6.6 LOOP 105

6.7 CASE versus IF 112

6.8 CASE versus WHEN 113

6.9 Bad Clocking 114

6.10 Using Sequential Code to Design Combinational Circuits 118

6.11 Problems 121

7 Signals and Variables 129

7.1 CONSTANT 129

7.2 SIGNAL 130

7.3 VARIABLE 131

7.4 SIGNAL versus VARIABLE 133

7.5 Number of Registers 140

7.6 Problems 151

8 State Machines 159

8.1 Introduction 159

8.2 Design Style #1 160

8.3 Design Style #2 (Stored Output) 168

viii Contents

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8.4 Encoding Style: From Binary to OneHot 181

8.5 Problems 183

9 Additional Circuit Designs 187

9.1 Barrel Shifter 187

9.2 Signed and Unsigned Comparators 191

9.3 Carry Ripple and Carry Look Ahead Adders 194

9.4 Fixed-Point Division 198

9.5 Vending-Machine Controller 202

9.6 Serial Data Receiver 208

9.7 Parallel-to-Serial Converter 211

9.8 Playing with a Seven-Segment Display 212

9.9 Signal Generators 217

9.10 Memory Design 220

9.11 Problems 225

II SYSTEM DESIGN 231

10 Packages and Components 233

10.1 Introduction 233

10.2 PACKAGE 234

10.3 COMPONENT 236

10.4 PORT MAP 244

10.5 GENERIC MAP 244

10.6 Problems 251

11 Functions and Procedures 253

11.1 FUNCTION 253

11.2 Function Location 256

11.3 PROCEDURE 265

11.4 Procedure Location 266

11.5 FUNCTION versus PROCEDURE Summary 270

11.6 ASSERT 270

11.7 Problems 271

12 Additional System Designs 275

12.1 Serial-Parallel Multiplier 275

12.2 Parallel Multiplier 279

Contents ix

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12.3 Multiply-Accumulate Circuits 285

12.4 Digital Filters 289

12.5 Neural Networks 294

12.6 Problems 301

Appendix A: Programmable Logic Devices 305

Appendix B: Xilinx ISE BModelSim Tutorial 317

Appendix C: Altera MaxPlus IIBAdvanced Synthesis Software

Tutorial 329

Appendix D: Altera Quartus II Tutorial 343

Appendix E: VHDL Reserved Words 355

Bibliography 357

Index 359

x Contents

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Preface

Structure of the Book

The book is divided into two parts: Circuit Design and System Design. The first part

deals with everything that goes directly inside the main code, while the second deals

with units that might be located in a library (for code sharing, reuse, and partitioning).

In summary, in Part I we study the entire background and coding techniques of

VHDL, which includes the following:

Code structure: libraries, entity, architecture (chapter 2)

Data types (chapter 3)

Operators and attributes (chapter 4)

Concurrent statements and concurrent code (chapter 5)

Sequential statements and sequential code (chapter 6)

Objects: signals, variables, constants (chapter 7)

Design of finite state machines (chapter 8)

And, finally, additional circuit designs are presented (chapter 9).

Then, in Part II we simply add new building blocks, which are intended mainly for

library allocation, to the material already presented. The structure of Part II is the

following:

Packages and components (chapter 10)

Functions and procedures (chapter 11)

Finally, additional system designs are presented (chapter 12).

Distinguishing Features

The main distinguishing features of the book are the following:

It teaches in detail all indispensable features of VHDL synthesis in a concise

format.

The sequence is well established. For example, a clear distinction is made between

what is at the circuit level (Part I) versus what is at the system level (Part II). The

foundations of VHDL are studied in chapters 1 to 4, fundamental coding in chapters 5

to 9, and finally system coding in chapters 10 to 12.

Each chapter is organized in such a way to collect together related information as

closely as possible. For instance, concurrent code is treated collectively in one chap￾TLFeBOOK

ter, while sequential code is treated in another; data types are discussed in one chap￾ter, while operators and attributes are in another; what is at the circuit level is seen in

one part of the book, while what is at the system level is in another.

While books on VHDL give limited emphasis to digital design concepts, and books

on digital design discuss VHDL only briefly, the present work completely integrates

them. It is indeed a design-oriented approach.

To achieve the above-mentioned integration between VHDL and digital design, the

following steps are taken:

a large number of complete design examples (rather than sketchy or partial

solutions) are presented;

illustrative top-level circuit diagrams are always shown;

fundamental design concepts are reviewed;

the solutions are explained and commented;

the circuits are always physically implemented (using programmable logic devices);

simulation results are always included, along with analysis and comments;

finally, appendices on programmable devices and synthesis tools are also included.

Audience

The book is intended as a text for any of the following EE/CS courses:

VHDL

Automated Digital Design

Programmable Logic Devices

Digital Design (basic or advanced)

It is also a supporting text for in-house courses in any of the areas listed above,

particularly for vendor-provided courses on VHDL and/or programmable logic

devices.

Acknowledgments

To the anonymous reviewers for their invaluable comments and suggestions. Special

thanks also to Ricardo P. Jasinski and Bruno U. Pedroni for their reviews and

comments.

xii Preface

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I CIRCUIT DESIGN

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