Abstract: A bus system for a printing machine, in particular a sheet-fed offset printing machine, which includes a plurality of stations designed as computers, which are connected to one another via a bus. In the bus, it is intended that potential errors which occur at unforeseeable times can be detected, without it being necessary to intervene in the line system of the bus. According to the invention, this is achieved in that at least one of the stations has a bus coupler whose transmitting portion is designed for the purpose of outputting bus signals for the purpose of establishing a connection to the other stations, the value of at least one physical variable differing from the value of this variable provided in the line protocol. In the case of a bus designed as an optical waveguide, this is advantageously achieved by one station carrying out the attempt to establish a connection initially at a low transmitted power.