| 摘要 |
A memory unit in which preselected program words stored in some of the memory locations are modified before transmission to the output pins of the memory unit, in order to protect those program words against illegal copying. When a jump instruction is decoded, the decoder issues a command to a random number generator 19, to an adder 25 and to a subtractor 26. The adder adds the random number output by the generator to the destination address of the pump instruction to form a pseudo-jump address which is sent to the processor 14. When the processor subsequently addresses the memory 12 to acquire the program word, the pseudo-jump address is converted to the original destination address by the subtractor. Copying pseudo-addresses results in the copied program being useless. Address tables may be used instead of the random number generator, adder and substractor. <IMAGE> |
