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The advent of relatively high speed computer graphics systems offers an attractive means by which the designer can more effectively perform his tasks. This paper describes an approach in designing and analysing logic control systems through the use of a VAX 11/780 mini-computer equipped with interactive graphic displays. The software primarily includes a logic circuit simulation program with various application processors which provide a communication link between the graphics, the data base and the simulation program itself. The system allows the user to create interactively on a colored graphic screen, a logic ladder diagram; the resulting information will be carried by the data base which provides necessary input to run the simulation program. The latter accepts logic input conditions imposed by the user to the control circuit then simulates appropriate component logic switchings and updates the data base accordingly. The user can also introduce various types of abnormal operating conditions into the system in order to verify the capability of the control circuit to satisfy the process safety requirements.