Non-volatile semiconductor memory device capable of being erased and written electrically

Abstract

Abstract PURPOSE:To protect important data from disappearance by providing a write enable flag for each storage data, stored in an EEPROM. CONSTITUTION:A second EEPROM cell group 6 stores an enable flag for indicating whether the respective data of a first EEPROM cell group 1 is made to be a protection object or not, to them. Then, when the enable flag, read out at first, is 0, a write signal W effective to write is not outputted from a rewrite control circuit 4, because a flip flop FF 5 latches 0. As the result, the data of the cell group 1, now being selected, is never rewritten and is reserved. Besides, in the case of erasure, read-out is performed at first, and the FF 5 is made to latch the enable flag. When the output of the FF 5, i.e., the enable flag is 1, an erase signal E' effective to the erasure is outputted from the control circuit 4, and the data of the cell group 1 of the selected address is erased. On the other hand, when the enable flag is 0, the data of the cell group 1 is reserved without being erased, because the signal E' is not outputted from the control circuit 4.

Inventors

• 👤 Noboru Kawamata

Bibliographic Details