A device for manipulating an operating state of a deterministic communication system is provided, which communication system includes a physical data bus, a plurality of nodes connected thereto, and an arrangement for transmitting messages in message frames at fixedly predefined communication cycles. The device is situated in the data bus between at least one node, from whose point of view the operating state of the communication system is manipulated, and the other nodes of the communication system. To make any desired manipulation of the operating state of the communication system possible, the manipulation device includes an arrangement for short-circuiting the data bus (2) and/or interrupting the data bus.