VHDL: Programming By Example, Fourth Edition
No matter what your current level of expertise, nothing will have you writing and verifying concise, efficient VHDL descriptions of hardware designs as fast or as painlessly as this classic tutorial.
TABLE OF CONTENTS VHDL: Programming By Example, Fourth Edition
Appendix D: VHDL93 Updates
Early in 1993 the VHDL language standard was updated to reflect a number of shortcomings with the VHDL 1076-1987 standard and to add some new features to the language. This new standard is called VHDL 1076-1993. In this appendix the 1987 standard will be referred to as VHDL87 and the 1993 standard as VHDL93.
The goal of this appendix is not to give the user a complete description of every new or changed feature, but to give the reader an idea of the scope of these changes and what effect they will have on future VHDL modeling efforts.
The goal of the update was to remain compatible with VHDL87 so that VHDL87 models would work in a VHDL93 environment. This goal was not entirely achieved as some of the new features were no longer compatible. The main reason for the incompatibility was the use of new keywords in VHDL93, that may have been used as identifiers in VHDL87, and a major update of TEXTIO.
The rest of this appendix includes discussions of the VHDL87 features that have either been added or changed. They are listed in alphabetical order for easier access.
Alias
The alias clause has been generalized for VHDL93. In VHDL87 an alias was used to give an alternate name to an object (see Chapter 8, Advanced Topics ). In VHDL93 the alias construct has been generalized to allow aliasing not only types but functions and procedures as well.
A typical alias in VHDL87 would look...
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