PURPOSE: To prevent a runaway by disabling an operation program, transferred from a ROM to a RAM, to be rewritten.
CONSTITUTION: The same addresses with the ROM 2 where the operation program of a CPU 1 is previously written are allocated to the RAM 3 for operation program writing, and when the processor is started up, the operation program is read out of the ROM 2 and transferred to the RAM 3. After the transfer of the operation program from the ROM 2 to the RAM 3 is completed, a transfer completion signal is outputted. On the basis of the transfer completion signal, the RAM 3 at the transfer destination is inhibited from being read out before and during the transfer of the operation program, and reading from the ROM 2 at the transfer source and writing to the RAM 3 at the transfer destination are inhibited after the transfer of the operation program is completed.
HAYAKAWA YOSHIYUKI
ONOZUKA TOSHIO
OTA HIDEKI
FUJI ELECTRIC CO LTD