Data communications method with two way communication between master and slave transceivers

摘要

A data communications system, e.g. for "hands free" personnel location or access control, comprises a master transceiver and a plurality of slave transceivers for transmitting individual identification messages to the master in accordance with a code in which binary values are represented by an infra-red transmission occuring during a first portion or a second portion of a bit period respectively. The master alternately echoes back to the slaves a binary value corresponding to the value last received. In the event of a clash, however, i.e. different values transmitted from different slaves during the same bit period, the master echoes back only a predetermined single value and the slave(s) which did not transmit that value then cease transmission. This process continues until one of the slaves has transmitted and had echoed back bit-by-bit the whole of its message. That slave then ceases transmission and the remaining slaves recommence until by repetition of the process all of the individual slave messages have been transmitted and echoed back.