Method and circuitry for causing sixteen bit microprocessor to execute eight bit op codes to produce either internal sixteen bit operation or internal eight bit operation in accordance with an emulation bit

摘要

A sixteen bit microprocessor includes an emulation bit that is loaded into an instruction register with 8 bit op codes. If the emulation bit is a "1", the 16 bit microprocessor operates internally as a 6502 type eight bit microprocessor, thereby emulating a 6502 microprocessor. If the emulation bit is set to a "0", the 16 bit microprocessor executes an instruction set of which the 6502 instruction set is a subset to effectuate internal 16 bit operation.