8.2. History
Hardware Description Language (HDL) is used by designers to describe circuit functionality in high level
language. This VHDL design is then processed to an implementable hardware circuit design.
The two main HDL solutions on the market are Verilog Hardware Design Language (Verilog) and Very
high-speed integrated circuit Hardware Design Language (VHDL). Although Verilog came on the market
much earlier than VHDL, they both have equal market share currently.
Verilog
Introduced by Gateway Automation in 1984 as a proprietary language.
Purchases by Synopsis in 1988 which was eventually purchased by Cadence Design Systems.
Cadence Design System has successfully has successfully market Verilog to a market power
house.
The syntax is similar to C language.
VHDL
The US department of Defense (DOD) and the IEEE sponsored the development of VHDL –
Standardized by IEEE in 1993.
Design may be decomposed hierarchically.
Each design element has a well-defined interface and a precise behavioral specification.
Behavioral specification can use either an algorithm or by a hardware structure.
Concurrency, timing, and clocking can all be modeled (asynchronous & synchronous
sequential circuit).
This chapter focuses on VHDL exclusively. There are sufficient similarity in structure and concepts
between VHDL and Verilog that learning Verilog is expected to be a simple process.