Patent ID: 7430678

Claim:
The method for executing, by a microprocessor, an instruction code including a first bit field used for controlling the microprocessor and a second bit field used for specifying opecode and/or operand, the method comprising: setting an operation mode of the microprocessor in a first mode or a second mode, the microprocessor executing an instruction code in a first instruction set in the first mode and executing an instruction in a second instruction set in the second mode; fetching an instruction code in either the first instruction set or the second instruction set from an instruction memory; extracting information from the first bit field of the instruction code so fetched; controlling the microprocessor based on the information so extracted and in the operation mode of the microprocessor; decoding the second bit field of the instruction code fetched in the fetching step; and executing the instruction code based on the decoding result, wherein the information contained in the first bit field in the first instruction set is different from the information contained in the first bit field in the second instruction set, and wherein a bit position of the first bit field is the same in the first instruction set and the second instruction set.