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.