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  • Pankaj Kaushal

VHDL - Understanding the Hardware Description Language

What is VHDL?

VHSIC Hardware Description Language (VHDL) is a programming language used to describe the hardware of a computer. Very High-Speed Integrated Circuit (VHSIC) is an abbreviation. It can be used to explain the structure and behaviour of electronic systems in general, but it's especially well suited to describing the structure and behaviour of digital electronic hardware designs like ASICs and FPGAs, as well as traditional digital circuits.

  • It's a hardware description language, which means it may be used to generate or design digital circuit/system hardware and can describe the behaviour of a digital circuit.

  • It can be used for both synthesis and simulation of digital circuits.

  • It is used to construct digital systems/circuits using Programmable Logic Devices such as CPLD (Complex Programmable Logic Device) or FPGA (Field Programmable Gate Array) (Field Programmable Gate Array)

  • VHDL code (program) is used to implement digital circuits in CPLDs and FPGAs, as well as to fabricate ASICs (Application Specific Integrated Circuit)

Advantages of VHDL

  • When used for systems design, VHDL has the benefit of allowing the behaviour of the needed system to be specified (modeled) and tested (simulated) before the design is translated into physical hardware via synthesis tools (gates and wires).

  • Another advantage is that VHDL may be used to describe a concurrent system. In contrast to procedural computer languages like BASIC, C, and assembly code, where a sequence of statements is performed sequentially one instruction at a time, VHDL is a data-flow language wherein every statement is examined for execution concurrently.

  • A VHDL project can be used for a variety of purposes. A computation block is built once and may be reused in several projects. Many formational and functional block properties, however, may be tweaked (capacity parameters, memory size, element base, block composition and interconnection structure)

  • A VHDL project can be moved around. A computer device project that was designed for one element basis can be transferred to another element base, such as VLSI with multiple methods.

VHDL Design

The first step is to develop VHDL code that meets these requirements. The code must be saved in a text file with the same name as its primary object and the extension “.vhd”. After that, a synthesis tool is used to build the code. During the compilation process, several files are created. The synthesizer breaks down the code into hardware structures that are available inside the chosen device. Each structure inferred by the synthesizer is allocated a specific location within the device during fitting (place and route).

This positioning information is crucial because it has a significant impact on the timing behaviour of the resultant circuit. The program allows the circuit to be completely simulated using the timing information obtained by the fitting procedure.

After the specifications have been completed, the designer may go on to the next phase (implementation), which involves creating a programming file for the device (if using a CPLD or FPGA) or the masks (if using ASICs). The design is completed in the case of CPLDs/FPGAs by downloading the programming file from the computer to the target device.


Basic VHDL Elements - Entity and Architecture

Any circuit's VHDL code is broken down into two sections: On the one hand, the entity describes the circuit's input and output ports. The architecture, on the other hand, explains the