| 摘要 |
PURPOSE:To allow an indoor telephone set to make a call to a door phone or to pick up the sound around the door phone by providing a function connecting the doorphone to a telephone set by the door phone call operation from the telephone set. CONSTITUTION:When a telephone set 512 hooks off, for example, a control circuit 16 controls a cross point circuit 31 to form the external line dial mode. When the telephone set 512 dials 0, an extension loop detector 28 sends the dial information to the control circuit 16. When no dial information exists for 3sec, the control circuit 19 controls the cross point circuit 31 to form the extension dial mode. When the telephone set 512 dials 7, the control circuit 16 controls the cross point circuit 31 to form the doorphone dial mode. When the telephone set 512 dials 3, the control circuit 16 establishes the doorphone talking state.
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