Multiline telephone answering system and interface therefor

An interface unit for selectively providing interconnection between a telephone line and an audio device such as a playback deck or the like comprising:

• connection circuitry for selectively making connection between a telephone line and an audio device, said connection circuitry having three modes of operation;
• means for setting the mode of operation of the connection circuitry;
• enabling means responsive to the connection circuitry being in a first mode and the presence of a ring signal on the telephone line for putting the connection circuitry in a waiting state;
• said connection circuitry including first switching means responsive to a first state of the audio device for making a connection between the telephone line and the audio device only when the connection circuitry is in the first mode and the waiting state;
• said connection circuitry further including means independent of the first switching means for making a connection between the telephone line and the device in response to a ring signal when the connection circuitry is in a second mode;
• said connection circuitry also including second switching means responsive to an external signal for making a connection between the telephone line and the audio device in response to the external signal, independently of the mode of the connection circuitry as set by the mode setting means;
• and
• means for inhibiting the enabling means when the connection circuitry is placed in a third mode of operation, without braking a previously existing connection through the connection circuitry between the telephone line and the audio device;