| 摘要 |
PURPOSE:To maintain the compatibility of existing software and to protect the security of a program by giving plural instruction sets and selectively using the different instruction sets in accordance with instruction fetch addresses. CONSTITUTION:An address decoder 2 normally selects RAM, decoding information is transmitted to an address control part 4 and an instruction which is read from RAM is held in a prefetch buffer 5. At the same time, a flag is set so that it selects the general-purpose instruction set. An instruction decoding part 6 refers to the flag 5, and an application is executed by the existing general-purpose instruction set. When a basic input/output control system (BIOS) program is executed, the decoder 2 selects a memory 3 and the flag 5 is set so that it selects the different instruction set which is individually developed. The instruction decoding part 6 refers to the flag 5 and executes the BIOS program by the original instruction set. Thus, the compatibility of existing software is maintained and security is protected. |
