In the current market context, industries need to constantly remain technically competitive. Such context in which customers require personalized products force them to design better products at shorter development cycles. In this regard, the process control of manufacturing systems greatly influences these factors. A simulation tool for process automation and control is proposed, which can simulate a Programmable Logic Controller (PLC) that can be programmed in Structured Text language, using multi-tasking. The simulator can be used to verify dynamical processes and controllers for discrete-event systems, discrete-time systems, and mixed systems. A description of the PLC simulation architectures and its development is provided, as well as illustrative examples.