Semiconductor memory device

Details Semiconductor memory device Semiconductor memory device

2005-04-26

2005-04-26

Elmore, Stephen (Department: 2186)

Electrical computers and digital processing systems: memory

Storage accessing and control

Control technique

C711S154000, C711S103000, C713S152000, C705S044000

Reexamination Certificate

active

06886087

ABSTRACT:
A semiconductor memory device reliably protects data written once into a non-volatile memory and exhibits high EEPROM data security functionality. The device has a user memory area to which a user can write freely chosen data, and a write-information storage memory area for storing information indicating whether or not data has been written into the user memory area. A control logic circuit analyzes whether to execute a write command from a user and outputs a write-prohibition signal if data is already written into the user memory area. The control logic circuit may include a password authentication circuit for authenticating a user-inputted password by comparing it with a password maintained inside the control logic circuit. The frequency of a changeable clock may be used to perform password authentication.

REFERENCES:
patent: 5048085 (1991-09-01), Abraham et al.
patent: 5184481 (1993-02-01), Joseph et al.
patent: 5818771 (1998-10-01), Yasu et al.
patent: 5912849 (1999-06-01), Yasu et al.
patent: 6681304 (2004-01-01), Vogt et al.

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