Hardware Description Language

Introduction:

       Most people are familiar with traditional programming languages like C, C++, Java, Python etc, which are used to develop software applications. However, many are unaware of Hardware Description languages like Verilog and VHDL. In this article, we will discuss about hardware description language. Let's go.

History:

The concept of a hardware description language as a medium for design capture was first introduced in the1950s, but wide adoption by the design community did not start until after 1985. Historically, the development of software programming languages stimulated the evolution of HDLs.

The first hardware description language came in late 1960, which looks like a traditional language. The first HDL was called "Description Language for Hardware" (DLH) and was developed by IBM in the late 1960s. However, it was not widely used because of its complexity and difficulty to use. In the subsequent years, various other HDLs came into existence such as ABEL and PALASM which gained popularity in the 1980s.

In the mid-1980s VHDL was introduced by the US Department of Defence.VHDL was designed to describe digital circuits, which aimed to develop high-performance digital circuits for military applications. In the same year, Verilog was introduced by Phil Moorby and Prabhu Goel owned by Gateway Design Automation. It was originally intended to be used for verification, but it became popular as HDL.

What is HDL?

In the history of Digital computers, various notations have been developed for capturing the logical behaviour of digital circuits at different levels of abstraction. Examples of such notations include boolean equations, timing charts, state transition tables, schematics, and hardware description languages. 

Hardware Description Language (HDL) is a programming language that is used to describe the structure, behaviour and timing of electronic circuits, and most commonly, digital logic circuits. HDLs are used for designing processors, motherboards, CPUs and various other Digital circuits. In addition to their use in circuit design, HDLs serve the purpose of simulating the circuit and verifying its response. Many HDLs are available, but the most popular HDLs so far are Verilog and VHDL.

• HDLs resemble a traditional programming language, but they are not identical. These are specifically designed to describe the hardware.
• Unlike traditional programming languages that primarily represent serial operations, HDL distinguishes itself by representing extensive parallel operations.

Purpose of HDLs:

HDLs allow for behavioural, register transfer, gate, and switch level logic, allowing designers to define levels in detail. Behavioural level logic allows for a set of instructions executed sequentially, and register transfer level logic allows for the transfer of data between registers, driven by an explicit clock and gate level logic, which defines the individual gate level logic. Similar to the relationship of HTML and CSS to web development, Verilog/VHDL has a similar relationship to FPGAs and other configurable logic devices. HDLs can be used to design and describe the layout of digital systems from simple flip-flop memory units to complex communications protocols.

Circuit Design: It provides a way to design digital circuits that meet the required specifications.

Simulation: It helps the designer to test and verify the digital circuit before it is built.

Verification: It provides designers to verify the functionality of the Digital circuit by testing it against different inputs and ensuring that the circuit functionality is correct and meets the desired functionality.

Synthesis: HDLs can be used to synthesize digital circuits. Synthesis is a process of automatically generating circuits from HDL code.

Timing Analysis: It provides designers to analyse the timing behaviour of digital circuits and ensure that the circuits meet the timing requirements.

Design Reusability: HDLs provide a way to design reusable components that can be used for multiple circuits design and reduce time and effort, which improves overall design quality.

Optimization: It Provides a way to optimise the design of digital circuits for performance.

Popular HDLs:

There are several HDLs available but the most popular HDLs are Verilog and VHDL.

Verilog: Verilog stands for verification logic. It is used to model and stimulate the Digital circuits Application-Specific Integrated Circuits (ASICs) and Field-Programmable Gate Arrays (FPGAs).

Syntax:
module module_name(inputs,output)
//statements
end module

VHDL:  VHDL stands for Very High-speed Integrated Circuit Hardware Description Language (VHSIC). It is used to design digital circuits. It is often used to design complex Digital circuits such as Microprocessors and Digital Signal Processors.

Syntax:
library ieee;
use ieee.std_logic_1164.all;
entity Circuit_name is
    Port ( a : in  STD_LOGIC;
         b : in STD_LOGIC;
           out1 : out STD_LOGIC);
end Circuit_1;
-----------------------------------------------------
architecture Behavioral of Circuit_name is
begin
// statements
end Behavioral;