| 摘要 |
PURPOSE:To protect the secrecy of a program data stored in a 1st EPROM by inhibiting the read of the program data out of the 1st EPROM with use of the output of a coincidence detecting circuit obtained when no coincidence is obtained between the program protection data and the read grant data. CONSTITUTION:When the memory contents of an EPROM 1 are protected from users, a program mode signal is set at '1' and therefore a buffer 11 is driven. Then the 8-bit program protection data is written into a data protecting EPROM 9 via the buffer 11. Thus the '0' output is obtained from a coincidence detecting circuit 14 and an AND gate 17 is cut off due to a fact that no coincidence is obtained between the contents of the EPROM 9 and those of a read grant register 12. As a result, it is inhibited to output the program data stored in the EPROM 1 through an input/output port 15. Then the secrecy of the program data can be protected. |
