Key telephone system

摘要

A key telephone system for use in PCM telecommunications includes an office line communication units, an extension interface unit, a receiving unit, an extension communication unit, and an information transmitting and receiving unit. The system further includes a timing setting unit for setting the timings for transmitting and receiving information from and to each of the office line communication unit, the extension interface unit, the receiving unit, the extension communication unit, and the information transmitting and receiving unit in which downstream information, which is applied from the extension interface unit to a plurality of terminal units, contains a start bit, bits expressive of data information, and bits expressive of parity information in each of a plurality of frames, contains bits expressive of control information in at least one of the frames, and contains frame-synchronization information for achieving the synchronization of frames in at least one of the frames, and upstream information, which is applied from the terminal units to the receiving unit, contains the bits expressive of the data information, the bits expressive of the parity information, and the bits expressive of the control information, and one of the downstream and upstream information is sent in the former half of each of the frames, and the other thereof is sent in the latter half thereof.