Browse Prior Art Database

Time Multiplexing Across Scarce Interface Lines

IP.com Disclosure Number: IPCOM000052748D
Original Publication Date: 1981-Jul-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Shasha, DE: AUTHOR [+2]

Abstract

Multiplexing onto busses is a common technique, but there are times when the overhead for tag bits is unacceptable. In a multiprocessing implementation, interprocessor communication lines must be held to a minimum. This article describes a way to multiplex information on interface lines without using tags. A simple sequence is described for carrying the same information as tagging without the overhead in interface lines.

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Time Multiplexing Across Scarce Interface Lines

Multiplexing onto busses is a common technique, but there are times when the overhead for tag bits is unacceptable. In a multiprocessing implementation, interprocessor communication lines must be held to a minimum. This article describes a way to multiplex information on interface lines without using tags. A simple sequence is described for carrying the same information as tagging without the overhead in interface lines.

A crossbar switch is used to select which of several elements are required by the Signal Processor instruction. Each element needs interface lines to and from all other elements. There were five conditions that could be sent, but our objective is to use only two binats for the encoding.

The sequencing scheme is: Encode Condition 00 1 01 2 10 3 11-0 4 11-11 5

The first three conditions are signalled by a sinangle two-bit code. The third and fourth conditions are signalled by two sequential two-bit codes, as shown in the above table. Microcode controls the sending portion of the crossbar. The receiving portions is decoded by the circuit shown in the figure, which shows a circuit that decodes the input from one sender for conditions 4 and 5.

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