Transmitting data between telephone subscribers - using data modem microprocessor for calling voltage detection when loop current flows

摘要

At each subscriber premises a data modem (MOD) connected to data terminal equipment (DEE), is centred around a microprocessor (CPU) which controls all operations with the aid of a RAM contg., e.g. the numbers of other subscribers. The modem (MOD) also incorporates an audio transmitter (TS) and receiver (TE). A loop current monitor (ISU) and a call voltage detector (RSE) are connected in and across the subscriber line (ASL) respectively. The operation ofa data key (DT) is also monitored (DTE) to distinguish between the called and the calling states of the appts.. ADVANTAGE - Data transmission in conformity with CCITT recommendations can be interrupted when two subscribers wish to communicate verbally. The channel position in duplex operation is unaffected and data exchange can be resumed immediately on replacement of handset.