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Browse Prior Art Database

Communication Line Multiplexer

IP.com Disclosure Number: IPCOM000061657D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Miller, EW: AUTHOR

Abstract

A communication line multiplexer card provides multiple communication interface ports which enable multiple devices to share a single communication facility, defined as a communication line and a supporting modem. Received signals are delivered to all interface ports in a multi- drop fashion, and transmitted signals are sequentially multiplexed onto the communication facility. Because all received signals are delivered to every interface port, each interface port must examine the address encoded in the header of a received message and discard messages addressed to other ports. For messages to be transmitted, the communication facility is sequentially made available to each port.

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Communication Line Multiplexer

A communication line multiplexer card provides multiple communication interface ports which enable multiple devices to share a single communication facility, defined as a communication line and a supporting modem. Received signals are delivered to all interface ports in a multi- drop fashion, and transmitted signals are sequentially multiplexed onto the communication facility. Because all received signals are delivered to every interface port, each interface port must examine the address encoded in the header of a received message and discard messages addressed to other ports. For messages to be transmitted, the communication facility is sequentially made available to each port. When a port which is currently transmitting ends its transmission, signalled by the port negating its Request to Send (RTS) signal, card arbitration logic examines the RTS signal from the next port in the allocation sequence. If this port's RTS signal is not asserted, the process is repeated for the next port in sequence. Once the arbitration logic finds a port which is ready to transmit, a Clear to Send (CTS) signal originating at the communication facility is passed on to the selected port. Whenever a port sees its CTS signal asserted, it may begin transmission. Since the communication facility is the originator of the CTS signal, the transmit operation should proceed normally from this point. Reclocking of data and timing signals may occur within the comm...