Modern process automation and control systems must be able to control discrete as well as continuous events. These events are sensed and controlled by distributed devices. Simulation is a necessity in order to design and tune the automatic control system. This paper addresses the advantages and disadvantages of using the discrete and continuous functions available in the control system to perform simulations. The simulation should run in real time for the purpose of operator training. The simulation should be transparent to the operator or user. Simulation should use generic building blocks to gain a wide variety of applications. As an example, the same simulator could be used to train both a nuclear reactor operator and a textile process operator. While this usually does not happen, it could become a necessity in an academic environment where fundamental concepts need to be taught to a variety of students with a minimal amount of duplication of effort.