Performance-Based Assessments for Digital Circuit Competencies

One lesson of digital circuits many students learn the hard way is the importance of not leaving CMOS inputs floating. In this case, the lesson is often learned in the form of leaving asynchronous inputs of the J-K flip-flops floating (preset, clear, or both). Be sure to check to see that all chip inputs are accounted for before passing students on this competency. If you see an input floating, touch the chip pin with a pen or pencil and let your students see the effect static has on their circuit!

I strongly recommend having students build their logic circuits with CMOS chips rather than TTL, because of the less stringent power supply requirements of CMOS.

Students are to research the datasheet for their particular IC and figure out from that what connections and timing sequences they need to make the circuit perform as requested. It is very important for students to learn to interpret manufacturers’ datasheets!

I recommend a slow clock frequency (1 Hz or so) to allow for easy viewing of the count sequence.