Very-high-speed integrated circuit (VHSIC) hardware description language (VHDL) is one of the languages commonly used to model the behavior of digital systems. VHDL is used to simulate, as well as to synthesize, digital circuits. This book is made up of two parts. The first part consists of nine chapters, and presents the basic features of VHDL that can be used to model digital circuit designs. The second part of the book, containing three chapters, presents the system design aspects of VHDL.

After an introductory chapter that provides an overview of the contents of the book, chapter 2 focuses on the typical code structure of a VHDL model. Two examples are used to introduce basic design units of VHDL.

VHDL is a strongly typed language, and, therefore, understanding the predefined and IEEE standard data types, operators, and attributes is essential to writing good VHDL models. In chapter 3, all fundamental data types, as well as means to develop user-defined data types, are presented. More emphasis is placed on the data types that can be synthesized into circuits. Chapter 4 introduces the basic operators supported in VHDL, followed by data and signal attributes. Finally, VHDL models that are easily modified or adapted are illustrated using the generics feature.

VHDL can be used to model concurrent as well as sequential operations in hardware. In chapter 5, basic constructs of concurrent VHDL, such as selected signal assignment, conditional signal assignment, the generate statement, and simple and guarded block statements are introduced. Chapter 6 covers the topics related to simple sequential code using process statements. Constructs used in the processes, such as if, wait, case, and loop statements, are illustrated using examples. Discussions related to the synthesis of sequential VHDL code and clocking will help novice designers.

Chapter 7 highlights the use of signals and variables. A number of design examples illustrate the appropriate use of signal and variable data types. State machines are models commonly used to describe sequential circuits. Chapter 8 focuses on VHDL code used to model Mealy and Moore state machines.

With the increasing complexity of digital systems, there is an immediate need to introduce the concepts of design partitioning, hierarchy, and reuse. VHDL provides features such as libraries, packages, functions, and procedures to facilitate system design. Chapter 10 introduces concepts relevant to developing packages and components. Component instantiation and port mapping are presented in this chapter. Functions and procedures used to model repetitively used or reused VHDL code are introduced in chapter 11. Finally, a number of simple system design examples are presented in chapter 12.

The increased use of VHDL by digital designers also coincides with the extensive use of field programmable gate arrays (FPGAs) and other programmable logic devices. Three appendices are provided as tutorials on the use of a VHDL-based synthesis of FPGAs from Xilinx and Altera.

The book presents numerous examples in each chapter that highlight related features of VHDL. The author uses these examples to provide a designer-friendly approach to introducing VHDL. The book, however, does not provide enough information about some simulation related features of VHDL, such as the concept of delays, the use of files to provide data for simulation, and the use of test benches. Adding a section or an additional chapter that addressed these topics would have made this work more complete. Otherwise, the author has done a tremendous job of introducing VHDL to novice digital designers, particularly in the coverage of VHDL’s synthesis features. This book will also be very useful as a supplement, to introduce VHDL concepts in introductory digital design courses.