Beginning in the mid 1980's, VLSI technology had begun to advance in two directions. Pushing the limit of integration, ULSI (Ultra Large Scale Integration) represents the frontier of the semiconductor processing technology in the campaign to conquer the submicron realm. The application of ULSI, however, is at present largely confined in the area of memory designs, and as such, its impact on traditional, microprocessor-based system design is modest. If advancement in this direction is merely a natural extrapolation from the previous integration generations, then the rise of ASIC (Application-Specific Integrated Circuit) is an unequivocal signal that a directional change in the discipline of system design is in effect. In contrast to ULSI, ASIC employs only well proven technology, and hence is usually at least one generation behind the most advanced processing technology. In spite of this apparent disadvantage, ASIC has become the mainstream of VLSI design and the technology base of numerous entrepreneurial opportunities ranging from PC clones to supercomputers. Unlike ULSI whose complexity can be hidden inside a memory chip or a standard component and thus can be accommodated by traditional system design methods, ASIC requires system designers to master a much larger body of knowledge spanning from processing technology and circuit techniques to architecture principles and algorithm characteristics. Integrating knowledge in these various areas has become the precondition for integrating devices and functions into an ASIC chip in a market-oriented environment. But knowledge is of two kinds.

too vast, too complex, too grand ... for description. John Wesley Powell-1870 (discovering the Grand Canyon) VHDL is a big world. A beginner can be easily disappointed by the generality of this language. This generality is explained by the large number of domains covered - from specifications to logical simulation or synthesis. To the very beginner, VHDL appears as a "kit". He is quickly aware that his problem may be solved with VHDL, but does not know how. He does not even know how to start. In this state of mind, all the constraints that can be set to his modeling job, by using a subset of the language or a given design methodology, may be seen as a life preserver. The success of the introduction of VHDL in a company depends on solutions to many questions that should be answered months before the first line of code is written: • Why choose VHDL? • Which VHDL tools should be chosen? • Which modeling methodology should be adopted? • How should the VHDL environment be customized? • What are the tricks? Where are the traps? • What are the differences between VHDL and other competing HDLs? Answers to these questions are organized according to different concerns: buying the tools, organizing the environment, and designing. Decisions taken in each of these areas may have many consequences on the way to the acceptance and efficiently use of VHDL in a company.

The VHSIC Hardware Description Language (VHDL) provides a standard machine processable notation for describing hardware. VHDL is the result of a collaborative effort between IBM, Intermetrics, and Texas Instruments; sponsored by the Very High Speed Integrated Cir cuits (VHSIC) program office of the Department of Defense, beginning in 1981. Today it is an IEEE standard (1076-1987), and several simulators and other automated support tools for it are available commercially. By providing a standard notation for describing hardware, especially in the early stages of the hardware design process, VHDL is expected to reduce both the time lag and the cost involved in building new systems and upgrading existing ones. VHDL is the result of an evolutionary approach to language devel opment starting with high level hardware description languages existing in 1981. It has a decidedly programming language flavor, resulting both from the orientation of hardware languages of that time, and from a ma jor requirement that VHDL use Ada constructs wherever appropriate. During the 1980's there has been an increasing current of research into high level specification languages for systems, particularly in the software area, and new methods of utilizing specifications in systems de velopment. This activity is worldwide and includes, for example, object oriented design, various rigorous development methods, mathematical verification, and synthesis from high level specifications. VAL (VHDL Annotation Language) is a simple further step in the evolution of hardware description languages in the direction of applying new methods that have developed since VHDL was designed.

ANALYSIS AND DESIGN OF DIGITAL SYSTEMS WITH VHDL integrates industry-standard hardware description language (VHDL) technology into the undergraduate digital logic course. Author Allen Dewey observes that the widespread use of VHDL in specifying digital system designs is driving change and innovation in industry, and defining a new skill set that engineering students must master to design, model, communicate, and implement digital systems. VHDL provides a formal mechanism for describing digital systems in a format easily processed by computers, succinctly capturing the basic concepts of digital systems engineering and harnessing the power of design automation technology. This book first presents combinational and sequential systems and their design, along with logic families and integrated circuits. It then interlocks these subjects with discussions of structural and data flow modeling, synchronous behavior, and algorithmic modeling of digital systems in VHDL. This dual-track organization of conceptual and VHDL-related material makes the book easily adaptable to one- or two-semester courses and a variety of teaching approaches.

A Guide to VHDL, Second Edition is intended for the working engineer who needs to develop, document, simulate, and synthesize a design using the VHDL language. It is for system and chip designers who are working with VHDL CAD tools, and who have some experience programming in Fortran, Pascal, or C and have used a logic simulator. A Guide to VHDL, Second Edition includes a number of paper exercises and computer lab experiments. If a compiler/simulator is available to the reader, then the lab exercises included in the chapters can be run to reinforce the learning experience. For practical purposes, this book keeps simulator-specific text to a minimum, but does use the Synopsys VHDL Simulator command language in a few cases. A Guide to VHDL, Second Edition is designed as a primer and its contents are appropriate for an introductory course in VHDL. The VHDL language was updated in 1992 with some minor improvements. In most cases, the language is upward compatible. Although this book is based primarily on the VHDL 1987 standard, this new second edition indicates the significant changes in the 1992 language to assist the designer in writing upwardly compatible code.

Synchronization is one of the important issues in digital system design. While other approaches have always been intriguing, up until now synchro nous operation using a common clock has been the dominant design philo sophy. However, we have reached the point, with advances in technology, where other options should be given serious consideration. This is because the clock periods are getting much smaller in relation to the interconnect propagation delays, even within a single chip and certainly at the board and backplane level. To a large extent, this problem can be overcome with care ful clock distribution in synchronous design, and tools for computer-aided design of clock distribution. However, this places global constraints on the design, making it necessary, for example, to redesign the clock distribution each time any part of the system is changed. In this book, some alternative approaches to synchronization in digital sys tem design are described and developed. We owe these techniques to a long history of effort in both digital system design and in digital communica tions, the latter field being relevant because large propagation delays have always been a dominant consideration in design. While synchronous design is discussed and contrasted to the other techniques in Chapter 6, the dom inant theme of this book is alternative approaches.

This book concerns a new method of image data compression which weil may supplant the well-established block-transfonn methods that have been state-of-the art for the last 15 years. Subband image coding or SBC was first perfonned as such in 1985, and as the results became known at first through conference proceedings, and later through journal papers, the research community became excited about both the theoretical and practical aspects of this new approach. This excitement is continuing today, with many major research laboratories and research universities around the world investigating the subband approach to coding of color images, high resolution images, video- including video conferencing and advanced tele vision, and the medical application of picture archiving systems. Much of the fruits of this work is summarized in the eight chapters of this book which were written by leading practitioners in this field. The subband approach to image coding starts by passing the image through a two- or three-dimensional filter bank. The two-dimensional (2-D) case usually is hierarchical' consisting of two stages of four filters each. Thus the original image is split into 16 subband images, with each one decimated or subsampled by 4x4, resulting in a data conservation. The individual channel data is then quantized ·for digital transmission. In an attractive variation an octave-like approach, herein tenned subband pyramid, is taken for the decomposition resulting in a total of just eleven subbands.

We would like to take this opportunity to thank all of those individ uals who helped us assemble this text, including the people of Lockheed Sanders and Nestor, Inc., whose encouragement and support were greatly appreciated. In addition, we would like to thank the members of the Lab oratory for Engineering Man-Machine Systems (LEMS) and the Center for Neural Science at Brown University for their frequent and helpful discussions on a number of topics discussed in this text. Although we both attended Brown from 1983 to 1985, and had offices in the same building, it is surprising that we did not meet until 1988. We also wish to thank Kluwer Academic Publishers for their profes sionalism and patience, and the reviewers for their constructive criticism. Thanks to John McCarthy for performing the final proof, and to John Adcock, Chip Bachmann, Deborah Farrow, Nathan Intrator, Michael Perrone, Ed Real, Lance Riek and Paul Zemany for their comments and assistance. We would also like to thank Khrisna Nathan, our most unbi ased and critical reviewer, for his suggestions for improving the content and accuracy of this text. A special thanks goes to Steve Hoffman, who was instrumental in helping us perform the experiments described in Chapter 9.