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Bidirectional Bus Interconnecting Multiple Stations With a Unique Set of Lines Assigned to Each Station for Transmitting Simultaneous Requests for Control of the Entire Bus

IP.com Disclosure Number: IPCOM000037377D
Original Publication Date: 1989-Dec-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Casper, DF: AUTHOR

Abstract

Two stations A and B are connected to communicate on a bus having several bidirectional lines. Station B can be a data channel and station A can be a component of a central processor that communicates with the channel.

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Bidirectional Bus Interconnecting Multiple Stations With a Unique Set of Lines Assigned to Each Station for Transmitting Simultaneous Requests for Control of the Entire Bus

Two stations A and B are connected to communicate on a bus having several bidirectional lines. Station B can be a data channel and station A can be a component of a central processor that communicates with the channel.

For a data transfer, one of the two stations has control of all of the lines of the bus. Operations on the bus are carried out under a predetermined protocol, and as an incident of this protocol, each station sets a latch to show which station has control of the bus.

When the stations first begin operations or whenever both stations simultaneously contend for control of the bus, control is granted to one of the stations on any suitable basis. For example, control can always be given to A.

For operations in which the stations contend for control of the bus, A is assigned some of the lines and B is assigned the other lines. A message on these lines is called a Request, and these lines will be called Request lines when they are used for this function. Both stations can use their Request lines at the same time. The stations can be assigned different numbers of lines.

A cycle for a normal data transfer is called a Data Cycle. When a station has control of the bus, it can execute any number of Data Cycles. When a stations contends for control of the bus, it operates in two cycles called a Decision Cycle and a Request Cycle.

During a Decision Cycle by A, A first tests its latch to determine whether B has control of the bus from a previous contention sequence. If B does not have control, A then tests B's Request lines to determine whether B has an active Request. (In this case, B is one cycle ahead of A in the execution of a request.) If B does not have an active request, A executes a Request Cycle by placing a request on A's Request lines.

The protocol includes several types of Request. Some Requests are called Commands. Some Commands begin on the Request Cycle but require a secon...