| 摘要 |
PURPOSE:To disable a third person to read out the contents of a ROM and analyze or copy a function by providing a single chip microcomputer with a built-in ROM and a built-in ROM external reading circuit for executing the logical operation of the contents of the built-in ROM and outputting the operated result to the external. CONSTITUTION:A built-in ROM external reading mode IR is set up to a low potential at the time of usual operation, and at the time of converting the potential level to a high potential, mode IR is adopted. The contents of the internal ROM 4 are read out to internal data buses D0 to Dn by a built-in ROM reading control signal R and the logical operation between bits '0' and '1' of the buses D0 to Dn is executed by an EXOR circuit 9 in an internal ROM reading circuit 5 and the OR result is outputted to a terminal Y0. The logical operation between bits '2' and '3' of the buses D0 to Dn is similarly executed and the OR result is outputted to a terminal Y1 and the logical operation between bits 'n-1' and 'n' is executed and the OR result is outputted from terminals Y0 to Yp. Since the logical operation of the contents of the ROM 4 is executed by the circuit 5 and the OR result is outputted, a third person can not detect the contents of the ROM. |
