Excerpt
Preface to Second Edition Synthesis seems to be the driving force in making VHDL a popular hardware description language. As the number of synthesis users has grown, so has the popularity and usage of VHDL. Today, VHDL is an IEEE standard as well as an ANSI standard for describing digital designs.
According to IEEE rules, the language must be reballotted every five years to continue to exist as a standard. VHDL was first standardzed in 1987, and the standard was called IEEE Std 1076-1987. The first edition of this book was based on that version of the language. In 1992, the language was reballotted, and after much deliberation, in 1993, a new standard called IEEE Std 1076-1993 was developed. In this version, a number of new features have been added, syntax for certain constructs has been made more consistent, and many ambiguities in the earlier version have been resolved. An appendix in this book summarizes the changes.
This edition of the book describes VHDL as defined in IEEE Std 1076-1993. Models described in the earlier version of the language are strictly upward-compatible, except for very minor changes; these changes are listed in the appendix. This edition of the book has been expanded to include descriptions of the new features and the syntax improvements made to the language. The format of the first edition has been retained. Changes from the first edition are not identified separately. Several examples have also been added. In addition, a number of suggestions made by readers of the earlier edition have been incorporated.
Acknowledgements
I am greatly indebted to Paul Menchini for reviewing this revised edition of the book and providing valuable comments and thoughtful criticism, which have resulted in an improved edition of the book.
J. Bhasker
April, 1994