Abstract: A digital communication bus upon which arbitration is distributed in a multiplicity of communicable interconnected bus interface logics supports unique signals to each associated on user device and upon the bus. Arbitration inhibiting signals, called inhibit request signals, allow any one(s) user device(s) to inhibit the new entrance, via requests, into arbitration of all other bus interconnected bus interface logics and associated user devices. Arbitration among bus interface logics already registering requests continues in priority order. Each user device may, via a signal called retract request, deregister, or cancel, requests previously registered at the associated bus interface logics to arbitrate for ownership of the bus. Each user device may, via a signal called stop bus, cause continuous interface logics while being precluded from recognition that arbitration should ever be won.

Abstract: The loading (writing) of plural successive data strings of specifiable bit-length and numbers to a scan/set testable register (called a CONTROL STORE SCAN LOOP STRING) from which it may then be transferred to a control store (called a CONTROL STORE (RAM)) both within a remote slave digital logic device (called a CENTRAL COMPLEX) is bit-serially conducted upon one signal line of a scan/set network by a controlling digital logic device (called a SUPPORT PROCESSOR) in substantially simultaneous time to the reading of the previous contents of such register (and control store) bit-serially via another signal line of said scan/set network. Both signal lines and devices together form a circular BIT-SERIAL SCAN LOOP, upon which the bit-serial writing and reading is time overlapped.