Data transmission system and method

摘要

A central station and a plurality of transmission stations are connected in cascade by a serial transmission line, and constitute a looped data highway system. The central station controls the whole system. The system allows the transmission station having a data signal transmission request to send out a data signal by means of a normal polling signal, but only the station having sent out the data signal by means of the preceding normal polling signal is allowed to send out the data signal again in response to a retry polling signal.