4.1   THE SOFTWARE TOOLBOX

Designing is a very exciting part of engineering. Leaving aside formal definitions, it is the phase of engineering where creativity and problem solving play the most important part. These activities allow explorations of design options by trial and error, engineering judgment, “guesstimation,” analysis, measurement, simulation, breadboarding, and so forth. There is normally an overall strategy, however, to guide the transition from specification to implementation, as discussed in Chapter 1. What the engineer must do is flesh out a complete behavioral, structural, and physical description so that a design can be built and tested. With these often onerous tasks and informal procedures, we can expect tools to “get in the way” of designing. The purpose of this chapter is to be informative about the applicability of tools for FPGA design and suggest fairly loose design process flows. The treatment is based on taking a simple design example, the 7-segment display driver, through a behavioral and structural design process. This example is conceptually simple, but it is a nontrivial 4-input, 7-output function. It is also a standard transistor-transistor logic (TTL) catalog part, the TTL7446. This serves to emphasize alternatives in design process flows as well as highlighting the relevance, or irrelevance, of specific tools.

This treatment is in distinction to some more conventional approaches, mostly as found in manufacturers’ literature, which often portray ...

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