In order to carry out data transfer among the subsystems of a bus oriented data processing system, each subsystem is coupled to the bus by a local bus adapter which controls both source and destination aspects of the information transfer. Each local bus adapter has a unique "busy" line which may be interrogated...http://www.google.ca/patents/US4038644?utm_source=gb-gplus-sharePatent US4038644 - Destination selection apparatus for a bus oriented computer system
