A graphical microcomputer simulator for classroom use

Educational aids for microprocessor courses are typically either hardware trainers or software simulators. The former enable the student to observe the details of I/O interfacing, but tend to be costly, at least to duplicate for many students, and provide only a limited view of the internal operations of the microprocessor. While more cost-effective, the latter are usually limited to displaying hexadecimal values written to I/O addresses with regard to peripheral interfacing. This paper describes a software simulator which illustrates microprocessor operation utilizing a graphical format designed for a PC-DOS platform. The simulator displays the registers and buses of a Motorola 6800 microprocessor. Instructions can be executed on a per-cycle or per-instruction (single-step) basis, with the bus logic values and register contents graphically changing at each step. A one-line assembler is available for writing programs into the 8 kByte RAM. In addition, an R6522 Versatile Interface Adapter (VIA) is also displayed. User-selectable peripherals include a hex keypad, 7-segment displays and an A/D converter. Online help screens are easily accessed. We have employed this simulator in our classes for two semesters and have found that students are able to learn it very quickly. It is an excellent tool for observing the details of microprocessor operation and interfacing to common peripherals.