Abstract: 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.

Abstract: A two-way CATV system having a substantial number of terminals incorporates a central processor and transmitter system which continually interrogates the terminals at high speed, monitoring changes of usage of premium programs and other data while also permitting central control of access to restricted premium programs. For inexpensive but reliable intercommunication, short, fixed word length digital messages are frequency multiplexed onto the cable in both upstream and downstream directions, and subscriber groups are controllably selected in turn, with each subscriber being scanned in what may be an arbitrary order by transmission of unique private messages which are recognized at the terminal and in response to which previously prepared fixed length messages are immediately transmitted in return.