Scan operation for a central processor

A central processor of the type which controls the operation of telephone exchange subsystems to establish requested service between telephone subscribers in response to a plurality of addressable multiple bit operational codes wherein each of the subsystems is connected to the central processor by a common data bus and assigned a discrete subsystem address for enabling the addressing of each subsystem and wherein one of the subsystems is a program memory containing the plurality of operational codes has a scan means for locating stored subsystem data which contains preselected bits of data responsive to a particular operational code which includes first and second partial subsystem addresses and a mode bit for specifying either a direct scan mode or an indirect scan mode.