Static information storage and retrieval – Floating gate – Data security
Reexamination Certificate
2002-03-11
2003-04-29
Nguyen, Tan T. (Department: 2818)
Static information storage and retrieval
Floating gate
Data security
C365S195000
Reexamination Certificate
active
06556476
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to computer data memory, and more particularly to devices and methods for protecting data in non-volatile memories.
2. Description of Related Art
It often occurs that computer files and databases that are accessible to certain persons should not be modifiable by those persons. For example, read only. Microsoft WORD has a save-file mode that allows the usual WORD file to be saved as read only.
There are two conventional methods for making data read-only. The first enforces the read-only mode with software programming, and the other uses circuit hardware to enforce read-only operation. Some designs use hardware write-protection to prevent noise or misaddressing from overwriting data inadvertently. Unfortunately, neither prior art method is trouble-free.
The software read-only protection generally depends on the manufacturer to define the protected-data areas. The user cannot change these borders. Thus when the data protection is enabled, it is impossible to reprogram that memory or file.
The hardware read-only protection generally requires a device pin to be pulled high or low. This is not real protection, because anyone can reprogram the data if they can get to the pin and pull it the right way. Such protection also operates only in blanket mode, either all the data in the chip is write-protected or it is not. Individual cells in the device are not manipulated for read/write protection.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a system for protecting data in memories.
Another object of the present invention is to provide a device that reprogrammably protects user data on a cell-by-cell basis.
Briefly, memory protection embodiment of the present invention comprises a memory device with two write modes. The memory device has many memory cells organized into pages. A normal write mode checks a one-bit flag collocated with every memory cell to see if writes are allowed. If the flag indicates a write operation to that memory cell is allowed, the flag is toggled and the cell is written. If the flag has previously been toggled, the write operation is prevented. A special write mode allows write operations to memory cells regardless of the state of the one-bit flag. The special write mode can be discerned in hardware by the loading of a register with a reprogrammable password, or the splitting of a normal single write-enable pin into two independent pins, e.g., normal write and special write. The memory operations can proceed either in page mode or cell-by-cell.
An advantage of the present invention is that a method is provided for protecting memory.
Another advantage of the present invention is that a memory device is provided that can protect its data contents.
The above and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5363334 (1994-11-01), Alexander et al.
patent: 5513136 (1996-04-01), Fandrich et al.
patent: 5592641 (1997-01-01), Fandrich et al.
Hill Robert Charles
Nguyen Tan T.
Unigen Corporation
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