16-11-2012, 04:35 PM
VHDL – (Introduction)
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Hardware Description Languages (HDL)
A computer language used to design digital circuits by entering text-based descriptions of the circuits.
Allows a digital system to be designed & debugged before conversion to gate and flip flop level
Popular languages
VHDL: Very High Speed Integrated Circuits Hardware Description Language
Verilog
VHDL – History
VHDL was the original and first hardware description language to be standardized by the Institute of Electrical and Electronics Engineers, through the IEEE 1076 standard.
A fundamental motivation to use VHDL (or its competitor, Verilog) is that VHDL is a standard, technology/vendor independent language, and is therefore portable and reusable.
(Applications of VHDL)
The two main immediate applications of VHDL are in the field of Programmable Logic Devices (including CPLDs—Complex Programmable Logic Devices and FPGAs—Field Programmable Gate Arrays) and in the field of ASICs (Application Specific Integrated Circuits).
Once the VHDL code has been written, it can be used either to implement the circuit in a programmable device (from Altera, Xilinx, Atmel, etc.) or can be submitted to a foundry for fabrication of an ASIC chip.
VHDL Design Structure
A VHDL design consists of 2 sections:
Entity
This portion declares the input/output/inout ports to the design. Ports are interfaces through which an entity can communicate with its environment. Each port must have a name, direction and a type.
Architecture
It describes the internal description of design, it defines the relationship between input, and output,