Introduuction to HDL

Introduuction to HDL

• We are familiar with the design of a digital system. The basic steps involved in this process are,

a. Specify the desired behaviour of the circuit.

b. Synthesize the circuit.

c. Implement the circuit.

d. Test the circuit to check whether the desired specifications meet.

• But as the size and complexity of digital systems increase, they can not be designed manually; their design becomes highly complex. At their most detailed level, they may consists of millions of elements, i.e. transistors or logic gates. So Computer Aided Design (CAD) tools are used in the design of such systems. One such a tool is a Hardware Description Language (HDL).

• HDL describes the hardware of digital systems. This description is in textual form. The Boolean expressions, logic diagrams and digital circuits (simple and complex) can be represented using HDL. The features of HDL are :

■ The HDL provides the digital designer with a means of describing a digital system at a wide range of levels of abstraction and at the same time, provides access to computer-aided design tools to aid in the design process at these levels.

■ The HDL, represents digital systems in the form of documentation which can be understood by human as well as computers.

■ It allows hardware designers to express their design with behavioral constructs. An abstract representation helps the designer explore architectural alternatives through simulations and to detect design bottlenecks before detailed design begins.

■ The HDL makes it easy to exchange the ideas between the designers.

■ It resembles a programming language, but the orientation of the HDL is specifically towards describing hardware structures and behavior. The storage, retrieval and processing of programs written using HDL can be performed easily and efficiently.

■ HDLs are used to describe hardware for the purpose of simulation, modeling, testing, design and documentation.

■ The most prominent modem HDLs in industry are Verilog and VHDL. Verilog is one of the two major Hardware Description Languages (HDLs) used by hardware designers in industry and academia. Of course, VHDL is the other one.

■ Verilog is very C-like and liked by electrical and computer engineers as most learn the C language in college. VHDL is very Ada-like and most engineers have no experience with Ada.

Review Questions

1. What is HDL ? Explain its necessity.

2. What is the need for VHDL ?