| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an intercom system that enables two-way communication only by using a pair of transmission lines, even if a physical layer of a local area network (LAN) is used. Ž<P>SOLUTION: An intercom slave unit 1 and an intercom master unit 2 includes transmission frame disassembly circuits 15, 25 for encapsulating and transmitting/receiving transmission data with preamble and idle to be used for a MAC frame of a LAN and LAN physical layer construction parts 16, 26 for converting the transmission data into physical layer data. Both the units are connected by a pair of transmission lines L1 each including a transmitting terminal and a receiving terminal among transmission lines constituting the LAN physical layer. Furthermore, broadband analog switches 17, 27 are provided for converting high/low impedance of the transmitting terminal and the transmission frame disassembly circuit 15, 25 switch the high/low impedance of the transmitting terminal in prescribed timing, thereby alternately implementing transmission/reception of encapsulated transmission data. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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