Patent ID: 7460560

Claim:
A method for operating an end user of an isochronous cyclical communication system comprising: providing a communication cycle of a connecting user having a first partial cycle for realtime communications and a second partial cycle for non-realtime communications; receiving a synchronizing data telegram, sent by the connecting user during the first partial cycle, by the end user, the synchronizing data telegram being subject to the propagation time of a transmission link between the connecting user and end user, and wherein the propagation time includes the propagation time of the synchronizing data telegram over a transmission link and the latency for triggering an interrupt in a connection of the end user; synchronizing a time base of the end user with the aid of the synchronizing data telegram, resulting in synchronizing of the time base with a tolerance corresponding to the propagation time; processing a transmission list from the end user within a communication cycle according to the end user's time base; and planning and executing transmission of a synchronizing data telegram from the connecting user, during the first partial cycle of a communication cycle, in accordance with the transmission list from the end user to the connecting user, and no earlier than at the start of the communication cycle and no later than by the tolerance before the planned forwarding time of the relevant data telegram, wherein the synchronizing data telegram is received by the end user when the end user's receive buffer is empty; and transmitting a realtime data telegram from the connecting user during the same first partial cycle wherein: the synchronizing data telegram is sent by the connecting user no earlier than after a maximum emptying time of the receive buffer of the end user after the start of the communication cycle.