Pedagogic computers

Laboratory experiments to familiarise students with the principles of digital control structures, such as computer processors, have in the past been difficult to implement because of the quantity and complexity of the equipment needed. Many institutions have constructed small computers from MSI components, requiring 20¿¿30 hours of a student´s time, and providing little, if any, scope for experimentation. A modular approach to the data part of a digital system may be provided with modern LSI components. If a similarly modular approach is taken to the design of the control part, it is possible for an elementary computer to be assembled in as little as two or three hours. Experimentation with a variety of computer processor designs and methodologies for the implementation of the control structure is then possible within the bounds of a short laboratory course, and first hand experience of design tradeoffs can be obtained. The paper describes equipment suitable for such teaching and discusses the design of several simple computer processors intended to provide experience of the use of digital control techniques in instruction format decoding, addressing mode implementation etc.