Importance

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Abstract

For a microcomputer system including a program memory and a microprocessor having means for executing sets of microinstructions which includes an instruction decoder and a microinstruction memory for storing the sets of microinstructions wherein each set of microinstructions is associated with a publicly known OP code, and wherein each set being activated in response to a related control word there is disclosed a method for securing from unauthorized copying a program stored in the program memory consisting of instruction words, with each instruction word including a control word wherein each of the instruction words is stored in a program memory external to the microprocessor. The method includes the steps of defining a set of proprietary control words wherein each proprietary control word is associated with a distinct publicly known OP code and its set of microinstructions of recording the program to be protected in the program memory with each instruction word including the proprietary control word associated with a desired set of microinstructions, and of fabricating the instruction decoder means and the microinstruction memory of the microprocessor so that each received proprietary control word is converted to the address of the microinstruction memory which stores the first microinstruction of the set of microinstructions associated with such received proprietary control word.

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First Claim