A Micro Programmable Simulator For Logic Design

Abstract

A class in logic design is a mainstay of most electrical and computer engineering programs and is typically taught in the sophomore year. Such courses cover Boolean algebra, combinational and sequential logic design, logic circuit analysis, and programmable logic devices. Many also provide an introduction to register level design and computer architecture. This paper presents the details of a simulation program that allows students to write microinstructions and some machine code for a simple machine. The program presents an easy-to-use graphical user interface and has options for a two-level and three-level pipelined machine. The program is currently in use in a sophomore level course in logic design as a mechanism to illustrate how a computer works and to introduce computer architecture concepts. I. Introduction Microprogramming is a concept dating back to the early 1950's 1 and is widely used in the design of modern computers. The concept is easy to understand and presents a general solution to the control problem for a central processing unit. Students who understand how microprogramming works from a logical point of view have insight into the inner workings and magic of digital computer systems that is difficult to obtain otherwise. An animated simulation of a microprogrammed computer in which a user can see the bits interacting with the hardware provides a vehicle for teaching what microprogramming is all about. The software described in this paper runs under the Windows XP operating system and is used in several projects in a sophomore-level electrical engineering class on logic design. It allows students to microprogram a simulated 8-bit computer and to visualize such architectural features as pipelining, the stored program, and the arithmetic and logic unit (alu) loop. II. Characteristics of the simulated machine The simulated machine is loosely based on the Intel 8080 8-bit cpu that dates back to the mid seventies. This machine has roughly the same register set, accumulator-based architecture, and ALU functions. It is however, microprogrammed (the 8080 was not) and it can be used in a pipelined mode (the 8080 had no pipeline). The architectural features of the machine are as follows: