MICROPROGRAMMED DATA PROCESSING UNIT INCLUDING A MULTI-FUNCTION SECONDARY CONTROL STORE

摘要

A microprogrammable control unit of a data processing unit includes first and second control stores. The first control store which is addressed initially by the operation code of a program instruction is used for storing a predetermined constant field coded to further specify the operation specified by the instruction operation code in addition to a control sequence field and address field. The second store stores a plurality of microinstruction sequences for executing the repertoire of program instructions. Control unit hardware decoder and sequencing circuits are conditioned by the control sequence field to execute a portion of the program instruction at the completion of which control is transferred to the second control store for completing execution of the program instruction under microprogram control. During the processing of various program instructions, the hardware sequencing circuits are operative to load signals corresponding to the constant field selected into one of a plurality of registers of the control unit. The constant signals selectively condition apparatus within the data processing unit enabling the hardware sequencing circuits and sequences of microinstructions from the second control store to execute the operation more particularly specified by the constant field in accordance with the operation code without requiring further decoding of such operation code.