JPH0828655B

PURPOSE:To prevent a CPU from malfunction at the time of the runaway of the CPU and to protect data in an EE-PROM by permitting the CPU to write data only when specific data are sent. CONSTITUTION:In case of writing data for the number of prints in the EE- PROM (electrical erasable programmable read-only memory) 4, a write control circuit 16 controls the EE-PROM so as to permit it to write data only for an allowable period. Specific data are sent to a write control circuit 16 through an address bus 5 and also sent to the EE-PROM 4 prior to the writing of data for the number of prints. Since the EE-PROM is constituted so as to be permitted to write data only when the specific data are sent, data writing in the EE-PROM is inhibited when a situation such as the runaway of the CPU 1 due to noise e.g. is generated, so that data writing in error can be completely removed and the data in the EE-PROM 4 can be surely protected.