US Patent 7403436 Non-volatile semiconductor memory device

When a non-volatile memory write error occurs in a card storage device containing a non-volatile memory and an error correction circuit, write data is read from the non-volatile memory and a check is made if the error can be corrected by the error correction circuit. If the error can be corrected, the write operation is ended. If the error correction circuit cannot correct the error, substitute processing is performed to write data into some other area.