SEMICONDUCTOR STORAGE DEVICE

PURPOSE:To make ID data nonvolatile and normally rewritable, and to prevent the ID data from being destroyed owing to malfunction by making a static RAM nonvolatile and adapting memory protection to a fixed data storage data area. CONSTITUTION:This device is equipped with the static RAM (SRAM) 4, a power source backup means 5 which backs up a power source when the normal power line to the SRAM is disconnected, an address decoder 3, and a write protection control circuit 7. Then the SRAM 4 is made nonvolatile by the backup means 5 and used while classified into a fixed data storage area 41 and a normal data storage area 42. Fixed data such as ID data which are made nonvolatile and memory-protected are stored in this fixed data in the fixed data storage area 42, normal data are read out and written in the normal data storage area 42. The need for a dedicated memory for fixed data storage is therefore eliminated. Consequently, the fixed data are held and normal writing is enabled.