Field-Programmable Gate Arrays: Reconfigurable Logic for Rapid Prototyping and Implementation of Digital Systems

1.5   DESIGN METHODOLOGIES

1.5.1   Describing a Design

There are many ways of describing a design and confusion over what a design description is. Diagramming templates and drawing boards have been replaced by electronic computer-aided design (CAD) products. Technology progress and the resultant increases in design complexity have extended simple circuit descriptions in terms of transistors, resistors, and capacitors to data bases that can include hierarchical schematics, hardware description language programs, simulation models, layout artwork, test patterns, and so on. This plethora of design data can be understood more clearly by separating design description and notation. To describe a design unambiguously, data must be created, or generated, in three domains of description: structural domain, behavioral domain, and physical domain. Figure 1–17 shows a Venn diagram representation and identifies the elements of design description in each domain. At the logic level a structural description could be a logic diagram, a behavioral description could be a set of logic equations, and a physical description could be a standard cell layout for an ASIC (or a fuse map for a PAL). Appropriate notations are used to create these descriptions, while different notations may be used to create different fragments of design. A read-only memory (ROM) will appear as a block in a logic schematic with its contents in a truth table.

In addition, complex designs are created by building up design descriptions ...