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Browse Prior Art Database

Multiplexing a Single Cycle-Steal Interface Among Multiple Devices

IP.com Disclosure Number: IPCOM000044040D
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Lochner, DL: AUTHOR [+2]

Abstract

Interface cards 2-4 in Fig. 1 allow connection of a number of subsystems to a single cycle-steal card 1 to attach those devices to a computer. Previous techniques required multiple cycle steal cards, resulting in higher costs and a considerable number of cables. It has been a common practice to include a circuit card of line drivers and receivers in a subsystem connected to a cycle-steal card housed in a computer, with each such subsystem having a dedicated cycle-steal card. The new Interface Card (Fig. 2) combines these drivers and receivers with added drivers and receivers to allow "daisy-chaining" of similar Interface Cards for other subsystems, as in Fig. 1. Interface Card 5 is essentially a multi-pole, double-throw switch, whose setting is chosen by some of the signals being switched.

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Multiplexing a Single Cycle-Steal Interface Among Multiple Devices

Interface cards 2-4 in Fig. 1 allow connection of a number of subsystems to a single cycle-steal card 1 to attach those devices to a computer. Previous techniques required multiple cycle steal cards, resulting in higher costs and a considerable number of cables. It has been a common practice to include a circuit card of line drivers and receivers in a subsystem connected to a cycle- steal card housed in a computer, with each such subsystem having a dedicated cycle-steal card. The new Interface Card (Fig. 2) combines these drivers and receivers with added drivers and receivers to allow "daisy-chaining" of similar Interface Cards for other subsystems, as in Fig. 1. Interface Card 5 is essentially a multi-pole, double-throw switch, whose setting is chosen by some of the signals being switched. Connectors mounted along the card's top edge accept cables from a cycle steal card or another interface card, and allow further cables to another interface card in a daisy-chain, as in Fig. 1. Each card, in sequence, chooses whether to pass signals between the primary connectors 10 and card tab pins 9, or between primary connectors 10 and extension connectors 11. This decision is made according to signals originating on the Cycle Steal card and recognized by Card ID Recognition Circuit 8. Control ripples through a number of daisy-chained Interface Cards until one recognizes its Card Identifier (Card ID) code on these control signals. A cycle steal interface device typically provides a number of data signal, and several control signals. The card on which this design is based includes a "Control Bus" for low-speed data transfer, and a "Data Bus" for high-speed transfer. The Control Bus is of interest here beca...