Memory designation control device

Claim 1

A memory designation control device comprising: a first rewritable memory device for storing a basic program; a second memory device, different from said first memory device, for storing a rewriting program for rewriting the contents of said first memory device; a mode selecting switch for switching between a normal processing mode in which normal processing based on the basic program is performed, and a rewrite processing mode in which rewrite processing based on the rewriting program is performed; means for bringing only said first memory device, out of said first memory device and said second memory device, into a selectable state when a system power supply is turned on while the mode selecting switch is in a state where the normal processing mode is selected; means for bringing only said second memory device, out of said first memory device and said second memory device, into a selectable state at the time of a read instruction, while bringing only said first memory device, out of said first memory device and said second memory device, into a selectable state at the time of a write instruction, when a system power supply is turned on while said mode selecting switch is in a state where the rewrite processing mode is selected; and means for inhibiting, when a system power supply is turned on while said mode selecting switch is in the state where the normal processing mode is selected, said second memory device from being brought into a selectable state if said mode selecting switch is switched to the state where the rewrite processing mode is selected after a system power supply is turned on.