JPH02214156A - Non-volatile semiconductor device - Google Patents

Abstract

PURPOSE:To surely protect a data by a method wherein the number of rewrite operations is limited at one part of an electrically erasable and programmable read-only memory element (EEPROM) and the data is fixed for a rewrite operation after the number of rewrite operations. CONSTITUTION:A memory cell array 1 composed of an EEPROM is constituted of a rewrite region 11 where a data can be rewritten and of a region 12 where the number of rewrite operations is limited. That is to say, before the data is written to the memory limitation region 12, a set value of a counter 9 until the data is fixed is serially input in advance from an external terminal; the data can be rewritten up to the number of rewrite operations of the set value; when the number is exceeded, the data can be fixed completely. Thereby, it is possible to protect them from an erroneous write operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a nonvolatile memory device using an electrically rewritable nonvolatile semiconductor as a memory element.

[Conventional technology]

Electrically rewritable non-volatile semiconductor (lla.

trioally Ierasable &! 1(l
Programmable ROIJ below KIFROM
When a high voltage of approximately -d got is applied to the corresponding memory cell according to the information corresponding to -1'H"L' according to the write mode signal given from the controller, the memory cell's Then, the tI value voltage changes and information is written.The methods of applying high voltage to the memory include providing a high voltage power supply terminal externally, and providing a booster circuit inside the XO. There is a method of boosting the voltage from a 5V power supply.

It's like the above! When an ItPROM is used as a storage element, there is a possibility that the data held in the IIIFROM will be destroyed when the power is turned on or off or when the applied voltage is momentarily interrupted. In other words, when applying a high voltage from a power supply via an external terminal, when applying a high voltage to a memory cell,
If the signal output from the controller becomes unstable due to power on/off or instantaneous power failure, the IO side may mistakenly enter write mode, and if a booster circuit is installed inside the xO, the power supply may become unstable. If the signal output from the controller becomes unstable due to on, off, or instantaneous power failure, there is a possibility that the write mode will be entered.

[Problem to be solved by the invention]

Conventional 1! Although tmpiov is electrically rewritable, in many cases, data is rewritten in some areas, but other areas are read-only, where the data once written is not rewritten, such as nROiJ. Therefore, from the user's point of view, in order to protect the written data from becoming corrupted due to the reasons mentioned above, which could be fatal to the system, Various measures are being taken.

For example, (1) Attach pull-up and pull-down resistors to the input terminals.

(2): [Attach the source detection circuit inside the IO or externally.

etc. are possible. However, there was a problem in that these measures were insufficient to completely protect against erroneous writing.The present invention was made to solve the above-mentioned conventional problems. Of these,
[Means for Solving the Problems] A nonvolatile semiconductor device of the present invention has a nonvolatile semiconductor device in which data is completely fixed when the number of rewrites exceeds a set number of times. Of the areas,
A limit is set on the number of rewrites, and an area is provided in which the data is completely fixed when the number of rewrites is exceeded.

[Effect]

In the nonvolatile semiconductor memory device of the present invention, when the number of rewrites is set, data is fixed only in a certain memory area when the number of rewrites is exceeded.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below based on the drawings. The figure is a block diagram showing the configuration of a nonvolatile semiconductor device according to the present invention. In the figure, (1) is a memory cell array consisting of an EEPRO IJ, and this memory cell array (1) includes a rewrite area OB where data can be rewritten and a rewrite area OB where data can be rewritten. Consists of area 0, which has a limited number of times. The rewriting regions α° C. and (6) are respectively connected to write circuits (2) or (3) that operate independently of each other.

The write circuits (2) and (3) each have a booster circuit (4).
) and (5), and the boost circuit (4) and (5)
is connected to a control circuit (6), and the control circuit (6) is connected to an external terminal (7). Further, the control circuit (6) is further connected to a counter (9), and the counter (9) is connected to an external terminal αG via a data input circuit (8).

Next, the operation will be explained with reference to φ.

First, before writing data to the memory limited area υ, a counter set value until the data is fixed is serially input from, for example, an external terminal QQ.

Next, the external terminal (7) is set to, for example, lOV or more, and writing is performed only when a certain mode set from another terminal is input. This writing can be rewritten only the number of times of the set value described above. For example, if the initially set value is 111, it can be rewritten only once. In this way, after a predetermined number of writes, the user can completely freeze the data. After the data is fixed, the external terminal (7) is set to Ov, for example, and it can be incorporated into the system and evaluated. Although the case where the normal write operation possible area is divided is shown, it is also possible to select a memory area using an address decoder within one memory area. Needless to say, an additional step for selecting an address is added.

〔Effect of the invention〕

As described above, according to the present invention, a part of the electrically rewritable memory element is limited in the number of times it can be rewritten, and the data is completely fixed against rewriting after the set number of times. 0 with excellent effect on reliable protection

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a non-volatile semiconductor device which is an embodiment of the present invention.
Memory array, (2)? (3)...Write circuit, (4) # (5)・°・Boost circuit, (6)...Control circuit, (8)...Input data circuit, +9)-...Counter, (7 ) l (10...external terminal, (2)...rewrite area, (2)...limited area for number of rewrites.

Claims (1)

[Claims] A nonvolatile memory device using an electrically rewritable nonvolatile semiconductor as a memory element, characterized in that a part of the memory area of the memory element is provided with a circuit that is completely fixed after rewriting. .