Browse Prior Art Database

Two Channel Switch

IP.com Disclosure Number: IPCOM000083791D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Cummings, KD: AUTHOR [+2]

Abstract

A two-channel switch (TCS) is provided for attaching a printer by way of two channels, to either a single processor that requires an alternate path capability or to two separate CPU's. The switching is done manually and only one channel interface is enabled at a time.

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Two Channel Switch

A two-channel switch (TCS) is provided for attaching a printer by way of two channels, to either a single processor that requires an alternate path capability or to two separate CPU's. The switching is done manually and only one channel interface is enabled at a time.

When a channel I/O operation over an interface is being executed, an I/O operation attempt by the second channel attached to the second TCS interface will cause a propagation of Select Out, Not Operational, to be presented on that channel.

A dynamic switching capability may be utilized and, in this case, both channel interfaces can be enabled at the same time and the selection of these interfaces is determined by programming; however, simultaneous operation over the two interfaces is not permitted.

When an I/O operation over one interface is being executed, an I/O initiation attempt by the second channel to the printer will cause Not Operational to be presented to that interface. Since the TCS allows only one I/O operation to be performed on only one of the two possible interfaces at any one time, this provides a data security capability and prevents two different systems from interleaving print lines on the printer. Any attempt by a second system to select the printer will result in an I/O error being presented to that system.

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