MICROPROGRAM CONTROL DEVICE

摘要

A microprogram control device controls a data path section provided in a CPU, which operates according to a microcode stored in a microprogram memory, by using a microprogramming method. The control device includes an instruction register for storing an instruction code which is received from a data bus and an address generator for generating an address signal from the output of the instruction register to access the microprogram memory. The address generator uses a first address decoder for decoding from a particular bit in the instruction code the type of instruction and a second address decoder for decoding from another particular bit of the instruction code the addressing mode of the instruction. A third address decoder is included for designating the timing for accessing the microprogram memory during each instruction cycle.