Abstract: A central processor for controlling the operation of the subsystems of a telephone exchange switching system which are interconnected on a common data bus to establish requested service between telephone subscribers, wherein the exchange system includes a program memory also connected to the common data bus for storing a plurality of selectable multiple bit operational codes to be utilized by the central processor in response to a particular service being requested, a program address register for selecting a desired operational code from the program memory, an instruction register for storing the selected operational codes and a control word generator which provides function control signals in response to the particular operational codes stored in the instruction register. A bit time counter coupled to the control word generator controls the timing of the central processor so that the function control signals are supplied in proper time sequence.