Entry point address circuit for microcode rom

摘要

A multiplexer (76) for coupling selected instruction word bits to a microcode memory (22) as entry point addresses. The multiplexer (76) receives sixteen bits from an instruction word register (10) and, for normal word formats, couples the opcode (40) portion unchanged to the memory (22) as an entry point address. For special instruction word formats, various bits of the instruction word fields form an entry point address, while other bits are modified and coupled to memory (22) as column addresses to access selected memory sections.