Method of operation and control program for a central unit in an automation system, and the central unit in an automation system and the automation system itself. A central unit (e.g., CPU) (1) in an automation system repeatedly executes a control program (8) that is stored in the central unit (1) and comprises at least two subprograms (TP1-TP3). A single instance of execution occurs within a cycle time (T) which is stipulated by the control program (8). The central unit (1) executes only one of the subprograms (TP1-TP3)—the activated subprogram (TP1-TP3)—at a time. The cycle time (T) is independent of the activated subprogram (TP1-TP3), is shorter than the time (t1+ . . . +t8) required in order to execute all of the subprograms (TP1-TP3), and is at least as long as the longest of the times (T1-T3) required in order to execute one of the subprograms (TP1-TP3) once.