Memory device with read access controlled by code

Details Memory device with read access controlled by code Memory device with read access controlled by code

1998-06-01

2001-05-08

Nguyen, Than V. (Department: 2759)

Electrical computers and digital processing systems: memory

Storage accessing and control

Control technique

C711S005000, C711S103000, C711S163000, C711S152000

Reexamination Certificate

active

06230244

ABSTRACT:

FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
The present invention relates to a memory device in which read access is controlled by the input of a code.
DESCRIPTION OF THE RELATED ART
This invention is applicable to, for example, various types of read-only memory (ROM), including both mask-programmable and electrically programmable ROM devices. ROM devices conventionally employ a two-line output control scheme in which read access is controlled by a chip enable signal and an output enable signal. When multiple ROM devices are connected in parallel to a common address bus, all of the ROM devices receive the same output enable signal, but each ROM device receives a different chip enable signal, which is generated by the decoding of address signals.
One disadvantage of this two-line control scheme is that an external address decoder is needed to generate the chip enable signals, and each chip enable signal requires a separate signal line. These requirements add to system size and cost.
Another disadvantage is that the size of the memory address space is limited by the number of address signal lines. Since each address selects a particular ROM device, it is not possible to re-use the same address in different ROM devices.
A further disadvantage is that any external device can read the memory contents, simply by driving two control signals to known active logic levels. There are situations in which access to the data stored in a memory device needs to be restricted. One example is the need to assure the security of confidential information stored in a read-only memory embedded in a smart card. Conventional memory devices lack an independent security protection function, making their data inherently vulnerable to unauthorized access.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to enable read access to a plurality of memory devices to be controlled without requiring a separate chip enable signal for each device.
Another object of the invention is to expand memory address space.
A further object is to protect memory contents from undesired read access.
A memory device of a preferred embodiment has a memory cell array with memory cells for storing data, a code input circuit for receiving a control code, a comparing circuit for comparing the control code with a predetermined code, and a read control circuit for controlling read access to the data stored in the memory cells according to the result of the comparison. Read access is controlled by, for example, enabling or disabling an address decoding circuit, an output buffer circuit, or a sense-amplifier circuit.
The control code is preferably input on address signal lines, a mode signal being used to distinguish between control code input and address input.
The predetermined code is preferably programmed into the memory device by the same method as used to program data into the memory cells. Mask programming or electrical programming can be employed. The predetermined code can be stored in special memory cells in the memory cell array.


REFERENCES:
patent: 4999770 (1991-03-01), Ara et al.
patent: 5237668 (1993-08-01), Blandy et al.
patent: 5319765 (1994-06-01), Kimura
patent: 5442704 (1995-08-01), Holtey
patent: 5787309 (1998-07-01), Greenstein et al.
patent: 2-300834 (1990-12-01), None
patent: 3-278151 (1991-12-01), None
patent: 4-170793 (1992-06-01), None
patent: 4-367045 (1992-12-01), None
patent: 5-233843 (1993-09-01), None
patent: 7-73033 (1995-03-01), None
patent: 7-105696 (1995-04-01), None
patent: 3-83491 (1996-03-01), None

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