Microprogram control system

A microprogram control system for executing macroinstructions comprising: (a) a microprogram read only memory for storing microinstructions which compose a plurality of microprogram routines given ones of which correspond to given macroinstructions, each macroinstruction including an operation code; (b) a microinstruction register coupled to receive and store microinstructions output from said microprogram read only memory; (c) a decoder coupled to receive and decode a microinstruction stored in said microinstruction register; (d) latch circuit means for storing an operation code of a macroinstruction to be executed, said latch circuit means being latched each time a microinstruction is read; (e) microprogram sequence control means for reading said microprogram read only memory; (f) a mapping read only memory for storing start addresses of the plurality of microprogram routines; (g) means for supplying input addresses to said mapping read only memory to index respective start addresses stored in said mapping read only memory of each of a plurality of microprogram routines corresponding to the macroinstruction having its operation code stored in said latch circuit means, said means for supplying including counting means, coupled to receive a signal from said decoder corresponding to a decoding of a JUMP instruction of a microinstruction and to increment its count in response thereto, said counting means being for generating an output count representing higher order bits of input addresses to said mapping read only memory and said means for supplying including coupling said latch circuit means to said mapping read only memory so that said operation code represents lower order bits of said input addresses; so that said mapping read only memory supplies respective start addresses indexed by said means for supplying to said microprogram sequence control means.