1. A data processor using microprogrammed control to execute a plurality of macroinstructions, the data processor comprising: a. first means for storing a macroinstruction; b. control means for storing a plurality of microinstruction routines, each of the microinstruction routines including one or more microinstructions for controlling operations performed by the data processor, and each of the microinstruction routines being associated with a corresponding starting address; and c. decoding means coupled to the first means and to the control means, the decoding means being responsive to a field of the macroinstruction stored by the first means for providing simultaneously a plurality of possible starting addresses associated with the execution of the stored macroinstruction, said decoding means being effective to selectively and sequentially present each of the plurality of starting addresses to the control means to cause each of the microinstruction routines associated with addresses provided by the decoding means to be executed in order to execute the stored macroinstruction.