VHDL can wear many hats. It is being used for documentation, verification, and synthesis of large digital designs. This is actually one of the key features of VHDL, since the same VHDL code can theoretically achieve all three of these goals, thus saving a lot of effort. In addition to being used for each of these purposes, VHDL can be used to take three different approaches to describing hardware. These three different approaches are the structural, data flow, and behavioral methods of hardware description. Most of the time a mixture of the three methods are employed. The following sections introduce you to the language by examining its use for each of these three methodologies. There are also certain guidelines that form an approach to using VHDL for synthesis, which is not addressed by this tutorial.
VHDL is a standard (VHDL-1076) developed by IEEE (Institute of Electrical and Electronics Engineers). The language has been through a few revisions, and you will come across this in the VHDL community. Currently, the most widely used version is the 1987 (std 1076-1987) version, sometimes referred to as VHDL'87, but also just VHDL. However, there is a newer revision of the language referred to as VHDL'93. VHDL'93 (adopted in 1994 of course) is fairly new and is still in the process of replacing VHDL'87.
The remainder of this tutorial discusses the use of VHDL'87 for hardware description and verification.
The previous section is A Brief VHDL Tutorial.
The next section is Structural Descriptions - Building Blocks.