Pre-emptive, rotational priority system

Abstract

A priority system in which eight priority request signals from eight associated requestors R7-R.phi. may simultaneously request access to an associated memory unit and may be honored in one of several priority modes. In a first mode the requestors R7-R.phi. are honored pre-emptively or in a numerically descending ordered manner in which priority selection is from the highest ordered priority requestor R7 first to the lowest ordered priority requestor R.phi. last. In a second mode the requestors R7-R.phi. are functionally divided into 4 groups of 2 requestors per group in which the priority request signals from the 4 groups 4, 3, 2, 1 of requestors may be selected pre-emptively, e.g., groups 4; 3; 2; 1 of requestors R7, R6; R5, R4; R3, R2; R1, R.phi. respectively, are honored in a numerically descending ordered manner in which the priority selection is from the highest priority group 4 first to the lowest priority group 1 last and in which priority between requestors within a group, e.g., requestors R5, R4 in group 3, is rotational such that in the event both requestors R5, R4 are requesting priority the requestor not last honored is honored first, e.g., if the higher ordered requestor R5 was last honored and requestors R5, R4 are now both requesting access to the memory storage unit, the order of priority will be rotated with the lower ordered requestor R4 having priority over the higher ordered requestor R5. Rotational priority between adjacent groups of requestors is also provided.