Computer circuit lab experiments using limited lab resources

Lab experiments in which students design and test functional parts of digital computers are useful endeavors that demonstrate how computer functions can be implemented and that reduce the mystery that surrounds computer circuits in students' minds. However, generating lab assignments that both involve significant processing functions and require manageable amounts of hardware is a daunting task for course instructors. Many educators have turned to simulation of digital circuits that implement computer functions, a decision that removes the student from the actual hands-on contact with circuits and components that are involved in. computer design. There is no better way to gain a gut feeling for how a circuit functions than to build it and make it work, including understanding the curious circuit behaviors that can result from misplaced wires or faulty components. Simulation separates the student from the operation of the circuit, and can increase the student's perception that the circuit is "too complicated" or "too mysterious" to implement on a breadboard. Often the most cumbersome part of a computer circuit implementation is providing input and output interfacing. The author developed a simple microcontroller-based instrument that implements a 12-key keypad input and a 16-character hexadecimal display for use in interfacing digital circuits, which was reported at an earlier ASEE conference¹. This paper reveals several lab experiments that have been performed by students to investigate digital computer functions, including arithmetic circuits such as multipliers and dividers and data structure implementations such as queues (FIFOs) and stacks (LIFOs). These lab experiments all have been completed by students using just a handful of standard logic chips plus the author's input/output instrument mentioned above. By breadboarding these circuits, rather than simulating them, students obtain a fuller understanding of how the circuits work and gain confidence in the design of computer systems.