A simulation model is developed for use in programmable controller ladder diagram testing. The developed model represent a physical flexible manufacturing system that can be controlled by different ladder logic diagrams. The model is capable of detecting initial ladder errors, displaying state changes in the ladder, and logging an operations history. As a result of the simulation development, insight into a generalized system descriptive language is obtained. This includes the language structure, specific data requirements, and an interface control method. The model also allows the user to locate optimal ladder solutions by comparing the results produced by different ladder diagrams. This thesis contains a literature review that establishes a history of programmable controller ladder testing and simulation modeling. The literature review provides impetus to the research by conveying the need for alternative methods of ladder diagram development, debugging, and testing. / M.S.