TABLE OF CONTENTS In this introductory chapter, we describe what we mean by digital system modeling and see why modeling and simulation are an important part of the design process. We see how the hardware description language VHDL can be used to model digital systems and introduce some of the basic concepts underlying the language. We complete this chapter with a description of the basic lexical and syntactic elements of the language, to form a basis for the detailed descriptions of language features that follow in later chapters.
If we are to discuss the topic of modeling digital systems, we first need to agree on what a digital system is. Different engineers would come up with different definitions, depending on their background and the field in which they were working. Some may consider a single VLSI circuit to be a self-contained digital system. Others might take a larger view and think of a complete computer, packaged in a cabinet with peripheral controllers and other interfaces.
For the purposes of this book, we include any digital circuit that processes or stores information as a digital system. We thus consider both the system as a whole and the various parts from which it is constructed. Therefore, our discussions cover a range of systems from the low-level gates that make up the components to the top-level functional units.
If we are to encompass this range of views of digital systems, we must recognize the complexity with which we are dealing. It is...
