VHDL - An Introduction and Background

VHDL is an acronym which stands for VHSIC Hardware Description Language. VHSIC stands for Very High Speed Integrated Circuits. The acronym is supposed to capture the entire theme of the language, that is to describe hardware much the same way we use schematics.

The language has been through a lot of revisions, and you will come across this in the VHDL community. Before 1981, different institutions developed their own HDL. Texas Instrument has its TI-HDL, General electric uses ZEUS HDL, IBM utilizes Interactive Design Language (IDL) while Computer Design Language (CDL) is an HDL developed for the academe. There are other HDL such as AHPL (A Hardware Programming Language), ISPS (Instruction Set Processor Specification), TDL (Tegas Description Language) and ConLan (Consensus Language- an attempt to establish a standard HDL). Not until the US Department of Defense (DoD), who else but the biggest funding source) sponsored a workshop on HDL at Woods Hole, Massachusetts in the Summer of 1981 to study the various HDLs to come up with a standard. In 1983, the DoD established the requirements for VHDL and awarded the contract to IBM, TI and Intermetrics to develop a standard VHDL resulting to VHDL 2.0 (allowed only concurrent statements), then in 1984 VHDL 6.0 (allowed sequential statements and corrected other shortcomings of VHDL 2.0). In 1985, VHDL 7.2 Language Reference Manual (LRM) copyright was transferred to IEEE (Institute of Electrical and Electronics Engineers).

In 1987, the IEEE VHDL LRM became the IEEE 1076 which is now known as VHDL’87. Currently, the most widely used version is the VHDL’87. 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.

Back to the syllabus: VHDL Syllabus.

The next section is The General Features of VHDL.

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Created for MS EcE, VHDL part of the Course – ECCE Department 2005