Communication device for data communication over a communication bus, comprising at least one data input bus connector (9a, 9b) provided for receiving data from the communication bus and each forming a data source, at least one data output bus connector (8a, 8b) provided for transmitting data over the communication bus and each forming a data sink, at least one data handling unit (7a, 7b) comprising at least one data input each forming a data sink, at least one data output each forming a data source, and a plurality of multiplexers wherein each of the data output bus connectors (8a, 8b) are connected to the output of a conjugated multiplexer and wherein one multiplexer is assigned to one data sink, characterized in that every data source is connected to the input of each of said plurality of multiplexers, so that each of the data sources can be selectively connected to each of the output bus connectors (8a, 8b) by control of at least one of the plurality of multiplexers, said communication device being provided for communicating with preceding and succeeding communication devices by connection to a downstream line and to an upstream line of the communication bus established in ring topology, wherein - a first data handling unit is a downstream line shift register comprising a data input forming a data sink and a data output forming a data source, - a second data handling unit is an upstream line shift register comprising a data input forming a data sink and a data output forming a data source, - a data processing unit is connectable to the first and second handling unit (7a, 7b) for receiving or transmitting digital data in a data stream communicated over the communication bus, - a first multiplexer is provided comprising one output port and at least four input ports, the output port of the first multiplexer being connected to the input of the first data handling unit and the output of the first and second data handling unit (7a, 7b) and the input bus connectors (9a, 9b) for the downstream line and the upstream line each being connected to a respective input port of the first multiplexer, - a second multiplexer is provided comprising one output port and at least four input ports, the output port of the second multiplexer being connected to the input of the second data handling unit and the output of the first and second data handling unit (7a, 7b) and the input bus connectors (9a, 9b) for the downstream line and the upstream line each being connected to a respective input port of the second multiplexer, - a third multiplexer is provided comprising one output port and at least four input ports, the output port of the third multiplexer being connected to the output bus connector for the downstream line of the communication bus, and the output of the first and second data handling unit (7a, 7b) and the input bus connectors (9a, 9b) for the downstream line and the upstream line each being connected to a respective input port of the third multiplexer, - a fourth multiplexer is provided comprising one output port and at least four input ports, the output port of the fourth multiplexer being connected to the output bus connector for the upstream line of the communication bus, and the output of the first and second data handling unit (7a, 7b) and the input bus connectors (9a, 9b) for the downstream line and the upstream line each being connected to a respective input port of the fourth multiplexer. - a first data handling unit is a downstream line shift register comprising a data input forming a data sink and a data output forming a data source, - a second data handling unit is an upstream line shift register comprising a data input forming a data sink and a data output forming a data source, - a data processing unit is connectable to the first and second handling unit (7a, 7b) for receiving or transmitting digital data in a data stream communicated over the communication bus, - a first multiplexer is provided comprising one output port and at least four input ports, the output port of the first multiplexer being connected to the input of the first data handling unit and the output of the first and second data handling unit (7a, 7b) and the input bus connectors (9a, 9b) for the downstream line and the upstream line each being connected to a respective input port of the first multiplexer, - a second multiplexer is provided comprising one output port and at least four input ports, the output port of the second multiplexer being connected to the input of the second data handling unit and the output of the first and second data handling unit (7a, 7b) and the input bus connectors (9a, 9b) for the downstream line and the upstream line each being connected to a respective input port of the second multiplexer, - a third multiplexer is provided comprising one output port and at least four input ports, the output port of the third multiplexer being connected to the output bus connector for the downstream line of the communication bus, and the output of the first and second data handling unit (7a, 7b) and the input bus connectors (9a, 9b) for the downstream line and the upstream line each being connected to a respective input port of the third multiplexer, - a fourth multiplexer is provided comprising one output port and at least four input ports, the output port of the fourth multiplexer being connected to the output bus connector for the upstream line of the communication bus, and the output of the first and second data handling unit (7a, 7b) and the input bus connectors (9a, 9b) for the downstream line and the upstream line each being connected to a respective input port of the fourth multiplexer.