Chapter 10 Introduction to VHDL

Introduction to VHDL As digital systems have become more complex, detailed design of the systems at the gate and flip-flop level has become very tedious and time consuming. For this reason, the use of hardware description languages in the digital design process continues to grow in importance. A hardware description language allows a digital system to be designed and debugged at a higher level before implementation VHDL is a hardware description language that is used to describe the behaviorand structure of digital systems.

Introduction to VHDL The acronym VHDL stands for VHSIC Hardware Description Language VHSIC in turn stands for Very High Speed Integrated Circuit. However, VHDL is a general-purpose hardware description language which can be used to describe and simulate the operation of a wide variety of digital VHDL was originally developed to allow a uniform method for specifying digital systems. The VHDL language became an IEEE standard in 1987, and it is widely used in industry

VHDL Description of Combinational Circuits VHDL leads naturally to a top-down design methodology The system is first specified at a high level and tested using a simulator.

VHDL Description of Combinational Circuits

Clock in VHDL

Clock in VHDL

VHDL example 1

VHDL example 2

Inertial delay model

VHDL Models for Multiplexers

Cascading MUXes

4-to-1 MUX

Testing 10-7 in VHDL

VHDL Modules: Example

Testing 10-8 in VHDL

VHDL Modules: General Form

Testing VHDL: 1 bit Full Adder

VHDL: 4-bit Full Adder

Simulating the 4-bit Adder

VHDL Syntax Signal: Constant: User defined types arrays:

ROM VHD Description

Latches and Flip-Flops

Input to output (simple Example)