The present invention is directed to a method of operation and a control program for a central unit (e.g., CPU) in an automation system repeatedly executing a control program that is stored in the central unit and comprises at least two subprograms. A single instance of execution occurs within a cycle time which is stipulated by the control program. The central unit executes only one of the subprograms—the activated subprogram—at a time. The cycle time is independent of the activated subprogram, is shorter than the time required in order to execute all of the subprograms, and is at least as long as the longest time period required in order to execute one of the subprograms once.