TIME INDEPENDENT DATA TRANSMISSION SYSTEM

摘要

A time independent data transmission system which allows a computer to access a remote data set at any time via non-dedicated telephone line is disclosed. The system is coupled to a telephone instrument, a data set and the telephone transmission line and normally connects the data set to the telephone transmission line. The telephone instrument is normally disconnected. In a preferred embodiment, a counting circuit senses the number of ring bursts in a ringing signal from a caller and a central computer is programmed to transmit a ringing signal having only one ring burst. When only one ring burst is sensed, the data set remains connected to the telephone transmission line and the data set begins to communicate with the central computer when the ringing signal terminates. If more than one ring burst occurs, a noncomputer call is being sensed and the data set is disconnected and the telephone connected to the telephone transmission line so that normal telephone usage is allowed. Communication between the computer and the data set via the telephone line occurs without ringing the telephone instrument and without otherwise interfering with normal telephone usage. In the event the user wishes to use the telephone instrument at any time, including the time when communication between the computer and data set is taking place, a subscriber priority circuit allows the user to recouple the instrument to the line by merely lifting the telephone handset and to decouple the instrument by replacing the handset.