The VHDL approach to electronic systems design

As we have said, VHDL is a language that enables both the function and the interconnect (when appropriate) of a system to be described. VHDL is a highly structured language with very strong typing. In particular, it is important to understand the difference in concept between signals and 

Sequential constructs enable the designer to describe the behaviour of the systems without specifying exactly the logic and interconnect required to achieve it. This is in contrast to the concurrent constructs, which go further down the path of describing discrete logic elements or modules with a clearer (if not fully defined) imderstanding of the physical circuit itself. 

Sequential constructs introduce many issues and concepts before a complete understanding is possible. Key ones include the following. 

Many design disdplines promote the use of modular design and building blocte to enhance design productivity, and VHDL is no exception. The building block approach simplifies the design process by splitting up the 

The particular VHDL constructs that support this include component instantiations, where other design elements can be seamlessly incorporated into a design (section 4.2.2) the use of procedures and functions to both partition the design task and facilitate top-down design techniques (section 6.2.2 for functions and section 7.3.2 for procedures) the use of blocks to structure the design description (section 7.2.2). 

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