G - Physics – 06 – F
Patent
G - Physics
06
F
354/232
G06F 9/46 (2006.01) G06F 13/36 (2006.01) G06F 13/364 (2006.01)
Patent
CA 1078524
Title of the Invention DESTINATION SELECTION APPARATUS FOR A BUS ORIENTED COMPUTER SYSTEM Abstract of the Disclosure In order to carry out data transfer among the sub- systems of a bus oriented data processing system, each sub- system is coupled to the bus by a local bus adapter which con- trols both source and destination aspects of the information transfer. Each local bus adapter has a unique "busy" line which may be interrogated by any local bus adapter connected to the bus. When a source subsystem wishes to transfer information to a destination subsystem, the source local bus adapter determines from the destination local bus adapter's busy line whether or not the destination subsystem is available to accept the informa- tion. If the destination subsystem is available, the source local bus adapter requests access to the bus from priority reso- lution apparatus. When the source request is granted, the source local bus adapter issues the message to the bus and also sets the destination local bus adapter's busy line to designate the busy state which indicates to the destination bus adapter that it must prepare to receive a message and also indicates to all subsequently requesting local bus adapters that the particu- lar subsystem to which information just placed on the bus is to be transferred is temporarily not available to receive informa- tion from any other local bus adapter. When the message has been received by the destination local bus adapter, both the source and destination local bus adapters enter a status cycle to check the integrity of the transmitted massage. If the message is received intact, both the source and destination local bus adapters complete their individual housekeeping tasks during which the destination local bus adapter tuns off its busy line. If an error has occurred during the message transmission, the destination subsystem, after the transfer has been retried once, disregards the message and turns off its busy line.
263608
Brooks Philip W.
Duke Jack R.
Elzer Robert R.
Na
Ncr Corporation
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