SECRECY PROTECTING CIRCUIT FOR SOFTWARE

摘要

PURPOSE:To protect the secrecy of the software by forming a cipher decoding part which decodes instruction words and outputs machine words to a CPU on the same chip with the CPU. CONSTITUTION:The software which is read out of a memory part 1 consists of ciphered instruction words, so the instruction contents can not be decoded even by connecting another software development tool, etc., to the output bus 30 of a memory part 1. Further, the decoding part 2 which decodes the instruction words and outputs the machine words to the CPU 3 is provided on the chip where the CPU 3 is formed, so the individual instruction contents can not be decoded by reading out the machine words. Consequently the secrecy of the software for operating the CPU 3 can be protected.