Digital program protection chip

摘要

The digital program protection chip has the purpose of preventing unauthorized use of digital computer programs which are stored in read-only memories in computers not authorized for this purpose. To this end, the program code is program-specifically stored under other addresses than the instruction counter addresses in the memory chip. The digital program protection chip performs the mapping of the addresses output by the processor to the associated memory addresses, which is necessary for error-free program running. To improve the protection, the program protection chip changes the address mapping after predetermined address sequences have been detected during the program run. In addition, it protects against attempts to read out the program from the processor side by means of emulator or word generator. The program protection chip cannot be copied and its operation is scarcely ascertainable because of the changes in the address mapping so that it cannot even be replaced by other circuits which can be duplicated.