Bridging The Gap Between Discrete And Programmable Logic In Introductory Digital Logic Laboratories

Most contemporary introductory digital logic design laboratories utilize discrete small-scale integrated (SSI), medium-scale integrated (MSI), and programmable logic such as field programmable gate arrays (FGPAs) or complex programmable logic devices (CPLDs). These more complex programmable devices (CPLDs and FPGAs) exhibit a superset of SSI and MSI functionality, enabling instructors to completely eliminate construction of circuits using SSI and MSI chips if they so choose. This paper describes the approach taken by the authors for introductory digital design laboratories in the Engineering Science Department of Trinity University, and explains some of the reasons for the given approach. The approach begins with construction of SSI and MSI circuits, includes a bridging laboratory where a complex SSI/MSI circuit is reimplemented in a CPLD, and finally moves to more complex designs utilizing no SSI/MSI constructs. The student base for introductory digital logic in our engineering program is quite broad, with all engineering students utilizing digital design in portions of two courses and a third optional course. This approach allows beginning students to benefit from the direct mapping from gate level design to implementation afforded by construction of circuits using SSI components. This is important, particularly to students of the “sensor” learning style. The bridging activity allows assimilation of concepts involving complex programmable logic without having confounding design concepts. Finally, the use of CPLDs with graphical or hardware description language design entry allows the construction of more complex designs than would be possible using only SSI/MSI components, and exposes the students to these useful modern tools. The mixture and progression of these techniques allows us to serve the various audiences in the Engineering Science program at Trinity, and allows us to incorporate complex programmable logic devices into the curriculum without losing several important features of the traditional introductory digital design laboratories.