Abstract: The present invention provides an improved arbitrator for use in allocating access to a common resource coupled to a plurality of data processing devices ("agents"). An arbitrator is coupled between the resource and each of the agents, for selectively enabling individual agents to access the resource in accordance with a predetermined priority hierarchy. The arbitrator, in the presently preferred embodiment, receives request signals transmitted by an agent desiring to access the resource and allocates ownership on a first come first serve basis or by a four level hierarchy in the case of simultaneous requests. The arbitrator includes a timing circuit which times predetermined periods between request signals transmitted by the agent which has acquired ownership. The arbitrator senses multiple requests for access by the agent within the predetermined time period, and, enters a lock condition if the agent issues a second request within the predefined period.