| 摘要 |
In a microprocessor-based controller 1, scrambled program data words are stored in a read-only memory 2 and user information is stored in a random-access memory 3. A data converter 12 is connected in a data bus 4b between the microprocessor 11 and the memories for descrambling data words when the ROM is accessed to produce a replica of original program data words and applying the replica to the microprocessor for operating the controller. The data converter simply applies data words to the microprocessor without descrambling when the RAM is accessed. In alternative embodiments (Figs 3, 5, 7) the scrambled program data words in the read-only memory may be divided into multiple data blocks, in which the original program data words have been scrambled by use of multiple keywords defined respectively for the data blocks. A modulo-2 adder is provided for summing each of the keywords with the scrambled program data words of a corresponding data block to descramble the data words. <IMAGE>
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