Abstract: The data address portions of a set of computer instructions are scrambled in accordance with a predetermined cipher key before the instructions are loaded into the instruction memory. The instructions with the scrambled data address portions are then loaded into the instruction memory at addresses corresponding to the original program sequence. The data involved in the program is loaded into a separate data memory at the addresses specified in the original unscrambled program. An unscrambler circuit which operates in accordance with the cipher key is coupled in series with the data memory address input conductors and is mounted on the data memory unit and is encapsulated therewith to prevent anyone from examining the unscrambler to determine the cipher key or from electrically interrogating the unscrambler in such a manner as to determine the cipher key.

Abstract: An analog signal which occurs in a computer controlled machine tool is converted to digital form at the machine tool site and is stored in a memory portion of the machine tool computer. The digitized analog signal is subsequently read out of the memory and is transmitted to a remote diagnostic unit via a conventional digital transmission link. The digitized analog signal received by the diagnostic unit is stored in a memory portion of the diagnostic computer and is subsequently read out and converted back to analog form for display on an oscilloscope in the diagnostic unit to aid in the diagnosis of existing or incipient faults in the machine tool.