Abstract: A single-channel communication bus system allows for the use of several master stations by way of an arbitration organization. A message contains a master address which is subjected to an arbitration operation, a slave address with space for a slave address acknowledge bit, a control signal with space for a control acknowledge bit, and one or more data bytes. Per data byte an indication of the "last" byte is also transmitted and space is reserved for a data acknowledge bit. When a data acknowledge bit is not correctly received, the data byte in question is repeated until at the most the maximum frame length is reached. The remainder of a message is then placed in a next frame. If an address or control acknowledge bit is not correctly received, the relevant frame is terminated.

Abstract: In a communication device with a star circuit all electrical bus connections are terminated by their characteristic impedance at the side of the stations as well as at the side of a star circuit. In order to enable arbitrary connection/disconnection of stations without modification of the terminating impedances while at the same time the termination remains optimum, each bus connection is provided with a separating element. This element receives an active bus connection state and communicates this state to all other connections so that the local bus connections are also activated. However, when a bus applied to the relevant separating element so that the latter cannot signal a further activation. Furthermore, for each connection there is provided a logic circuit in order to prevent the signalling of the own activation back to the own bus connection, while the inhibit signal for the own bus connection need not be active either.