Abstract: The present disclosure is directed to an arrangement whereby any one of a plurality of different or similar interface circuit cards can be located into any one of a number of slots or holding means of a data processing system, without preassignment thereto, and whereby each of the interface circuit cards will generate its own diagnostic routine signals and signals representing its own identification, the latter signals being used in a self-configuration operation of the system and whereby an arbiter means is employed to determine, among the plurality of interface circuits, which has the highest priority in the event more than one of said interface circuits is requesting the use of a common data flow path.