System for distributed priority arbitration among several processing units competing for access to a common data channel

摘要

A system for the exchange of messages among a multiplicity of processing units includes a data channel and a service line interconnecting respective interfaces of these units. Each interface includes a busy-state detector determining during a test phase of a recurrent time slot whether the service line is available, a logic network connectable in a subsequent acquisition phase the service line in the event of its availability to emit successive bits of an address characterizing the respective processing unit, and a comparator determining during the aquisition phase whether an emitted address bit of a particular logic level ("1") coincides with another bit of a higher-priority level ("0") concurrently sent over the line by some other unit. If a higher-priority address bit is encountered, the emission of the address is aborted and restarted in a subsequent time slot. If there is no conflict, an outgoing message is delivered to the data channel by way of a concurrently enabled driver; should that message require more than one time slot for its transmission, the service line is seized by the emission of a busy bit in the test phases of one or more subsequent time slots preceding the last time slot occupied by that message.