| 摘要 |
Method and system for data transmission between a central station and a number of terminal stations arranged on a closed loop. The transmission is carried out in series bit-by-bit in the one and same direction through the loop and in control of the central station. All data is transferred in the shape of data messages of a standard length, (e.g. 12 bits), each message comprising an address portion indicating the address of the terminal station to/ from which the message is directed, and a data portion comprising an information or control character. The messages are transferred as data blocks consisting of an output data phase during which at least one message is transmitted by central station to the terminal stations for which the central station has output data to send, a general polling character by which each output data phase is terminated and which prepares for transmission the terminal stations which have input data to send, and an input data phase during which at least one data message is transmitted from each terminal station prepared for transmission by the preceding polling character. The central station initiates a new transfer block as soon as the end of an input data phase is sensed, in which block the lengths of the output and input data phases are always adapted to the actual transfer need. |
