Browse Prior Art Database

Access Protocol for Bilateral Bus with Unilateral Control Wire

IP.com Disclosure Number: IPCOM000050375D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Fratta, L: AUTHOR

Abstract

This invention relates to a method for accessing a contention-free bilateral bus shared among N transceiving ports. A unidirectional signal wire also couples and orders (arranges) the ports 1,2..j..N. In the prior art, Eswaran (U.S. Patent 4,292,623) described a bus accessing protocol requiring each port to intent signal higher order ports j..N, pause for a stipulated period, and transmit on the bus only in the absence of a received intent signal from lower order ports 1..(j-1) and a free bus. Significantly, this art requires each port to lock onto the bus until message completion.

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Access Protocol for Bilateral Bus with Unilateral Control Wire

This invention relates to a method for accessing a contention-free bilateral bus shared among N transceiving ports. A unidirectional signal wire also couples and orders (arranges) the ports 1,2..j..N. In the prior art, Eswaran (U.S. Patent 4,292,623) described a bus accessing protocol requiring each port to intent signal higher order ports j..N, pause for a stipulated period, and transmit on the bus only in the absence of a received intent signal from lower order ports 1..(j-1) and a free bus. Significantly, this art requires each port to lock onto the bus until message completion.

In contrast, in this invention the ports are round robin scheduled accessing 1,2..N to the bus. This is modified by a port random-access capability. Thus, in addition to the intent signaling, pause, transmit if bus free protocol of the prior art, this method aborts the jth port's transmission responsive to an intent signal from another port. This spreads access statistics and avoids lockout by slow speed (long message) ports. These modifications require each port to keep a message copy until after transmission since the next bus access starts at the beginning of the message.

Restated, the protocol may be used on a bilateral bus to which access by the ports is round robin scheduled and supplemented by random accessing. Further, a connected port has its transmission aborted responsive to another port contending for access mod...