Bi-directional data communications system

摘要

A bi-directional data communications system including a single center facility and plural terminal control devices. A pair of up-data and down-data lines connect the central facility and the plural terminal control devices. Each of the terminal control devices includes a counter in which a specific numerical value is preset. A cycle start frame signal and data synchronizing frame signals are transmitted through the down-data line to the counter. The counter counts down from the preset value in response to the data synchronizing frame signals starting from a time determined by the cycle start frame signal. Transmission and reception of data are simultaneously carried out between the center facility and the terminal control device when the preset value and the number of the data synchronizing frame signals which have been counted are coincident.