| 摘要 |
PURPOSE:To disable a third person from decoding the data on the program of a microcomputer system by storing in an external ROM a conversion code which is converted to obtain a normal program data and to have a proper logic with a keyword code within an incorporated ROM. CONSTITUTION:A program developed by a user is coded with the use of a proper keyword group to obtain a conversion code, and this code is stored in an external ROM6. Thus the program decoding is difficult since the internal data is converted into the codes although the ROM6 can be freely read out. In this connection, the keyword group which is used to convert the program data into the codes is stored into an incorporated ROM2 with correspondence to an address. As a result, the corresponding keyword code is read out of the ROM2 as soon as the ROM6 is accessed. A logical circuit 13 obtains an exclusive OR between the data (conversion code) read out of the ROM6 and the keyword code. Thus the original data is produced and delivered to a data bus 4b. |
