Arbitration as provided in two separate levels, first between two signals that may contend for access to a system resource, such as a memory, and second between the winner of the first arbitration and another source, such as a refresh signal timer, that must have access to the system resource periodically...http://www.google.es/patents/US4597054?utm_source=gb-gplus-sharePatente US4597054 - Arbiter circuit and method
