Abstract: A telephone handset interface is inserted between the telephone handset and base for automatic switching between voice and data modes of communication. Each station includes a telephone set with a base and handset, interface circuitry, and modem. The interface circuitry includes relay switches to couple the modem to the telephone base microphone and speaker lines in data mode and to couple the telephone handset to the telephone base in voice mode. The relay switches are controlled by a sensor that monitors the on-hook/off-hook status of the modem as an indication of when the modem is preparing to transmit or receive data. The interface circuitry also includes differential amplifier circuitry coupled to the telephone base speaker lines that enables the modem to continually monitor the telephone base speaker lines. In one embodiment, each modem includes circuitry for generating a start signal to cause a remote station at the other end of the communication link to enter data mode prior to transmitting data.

Abstract: A telephone interface system is inserted between the telephone handset and base to provide automatic switching between voice and data modes of communication. The interface includes a modem having a receive port coupled to the telephone base speaker lines and a transmit port switchably coupled to the base microphone lines, a switch for selectively coupling the telephone handset to the base, and a processor for monitoring data received by the modem and controlling the switch to automatically decouple the telephone handset from the base when data is being received or transmitted by the modem. The modem includes a tone generator that generates a predetermined start signal to signal a remote unit at the other end of the communication link to enter data mode prior to transmission of data. Similarly, the modem includes a tone detector to detect a start signal sent by the remote unit that causes the unit to switch into data mode in preparation for receiving data.

Abstract: A microcomputer controlled circuit arrangement for sensing fire and burglar alarms in the presence of undesired fault conditions, such as opens or shorts, on monitored communication lines. The arrangement includes transistor-resistor sensing circuitry which is shared by a plurality of monitored communication lines, each of which comprises a first pair of conductors connected to a first contact of an alarm sensor and a second pair of conductors connected to a second alarm sensor contact. The sensing circuitry is connected through a multiplexer to each one of the lines one at a time under control of the microcomputer to detect any fault thereon and any alarm provided by the sensor contacts. The sensing circuitry is responsive to impedance conditions on the four conductors furnishing a plurality of output voltages which are examined by comparators that, in turn, generate combinational logic voltages signifying the alarm-fault state of a monitored line.