JP2004118885A - Method of erasing information of write once memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an erasing method of storage medium, capable of efficiently reading information stored in a storage medium such as a write once memory. <P>SOLUTION: When information read from a storage bit is not coincident with information written therein, a storage medium from which information is erased is identified to be a write once memory or the like. By writing information different from the written information is written in the storage bit, information of "0" or "1" pre-written in the storage bit is all rewritten to be information of "1" or "0", and thereby information can be erased. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for erasing information in a write-once memory.
[0002]
[Prior art]
For example, a memory card used in an electronic camera such as a digital still camera is generally a so-called flash memory in which image information or the like can be repeatedly written or erased arbitrarily.
[0003]
On the other hand, in recent years, a memory called a write-once has been developed. The write-once memory allows information to be stored and read, but cannot overwrite any new information, and is relatively inexpensive in structure. Therefore, if the write-once memory is used as the storage means of the electronic camera, even if the user wants to keep the captured image in the memory as it is, the cost burden on the user is reduced and the captured image can be easily stored. It is preferable because it becomes possible. The write-once memory is described in detail on the following URL homepage.
[Non-patent document 1]
URL http: // www. matrixsemi. com /
[0004]
[Problems to be solved by the invention]
By the way, since image information and the like can be arbitrarily written into the flash memory, the flash memory can be repeatedly used by overwriting the stored image information. Therefore, the information written to the flash memory, which is no longer necessary for the user but which the user does not want to be viewed by others, is automatically overwritten with the next information by the erasing process, thereby making reading impossible. Privacy and security issues are unlikely to occur.
[0005]
However, since the write-once memory cannot write an arbitrary image to the information that has already been written, the write-once memory can be used to read out information that is no longer necessary for the user but is not desired to be viewed by others. The question is how to block. Here, it is possible to reject the information read request by software, but as long as the information remains in the write-once memory, there is a possibility that the information may be read by some unusual means. On the other hand, by physically destroying the write-once memory, it is possible to make it impossible to read information, but it takes time and effort.
[0006]
The present invention has been made in view of the above-mentioned problems of the related art, and has been developed for a storage medium capable of efficiently setting information stored in a storage medium such as a write-once memory to an unreadable state. It is intended to provide an erasing method.
[0007]
[Means for Solving the Problems]
The method for erasing a storage medium according to the present invention is characterized in that the information recorded in the storage bits of the erasure target area is erased by writing single information to all the storage bits of the erasure target area of the storage medium. And
[0008]
Preferably, the method further comprises the step of determining the single information.
[0009]
Further, the step of determining the single information is a first step of reading information of a predetermined storage bit, and a step of reading information different from the information read in the first step in the storage bit read in the first step. A second step of writing the information of the storage bit after writing in the second step, a third step of reading the information of the storage bit written in the second step, and the information read in the third step matches the information written in the second step. It is preferable to include a fourth step of determining whether or not to perform.
[0010]
Further, when the information read in the third step matches the information written in the second step, the information written in the second step is determined as the single information, and the third information is determined. When the information read in the step does not match the information written in the second step, it is preferable that the information read in the first step is determined as the single information.
[0011]
In a storage medium such as a so-called write-once memory, before use, only one of information “0” and “1” (this is referred to as initial information) is written in advance in all storage bits. It has a function that can be rewritten to "1" (when the initial information is 0) or "0" (when the initial information is 1) only once. As a result, information such as image information can be obtained based on information obtained by combining “0” and “1”. The present invention utilizes this characteristic. Specifically, after writing information (for example, “1”) different from the information (for example, “0”) read from a certain storage bit of the storage medium on which the information is recorded, reading is performed again from the storage bit. If the information (e.g., "0") does not match the information (e.g., "1") written therein, the information is stored in the storage medium, and the information (e.g., "0") is already stored in the storage bit. ) Is written (that is, the initial information is “1”). This corresponds to determining the single information. This makes it possible to confirm that the storage medium is a write-once memory or the like. Thereafter, by writing information (for example, “0”) different from the written information to all the storage bits in the erasure target area, Erasing in that area can be performed reliably.
[0012]
On the other hand, in a storage medium such as a write-once memory, information (for example, “1”) different from information (for example, “0”) read from a certain storage bit is written to the storage bit, and then read from the storage bit again. If the information (e.g., "1") matches the information (e.g., "1") written therein, the storage bit is initialized to the initial information (e.g., "0") even though the information is stored in the storage medium. ). This corresponds to determining the single information. Therefore, by writing the same information (for example, “1”) as the written information to all the storage bits in the area to be erased, the erasure in that area can be performed reliably.
[0013]
Further, the single information is preferably information indicating “0” or “1”, but is not limited thereto. For example, the single information may be a specific erasure pattern.
[0014]
By the way, according to the above-described invention, it is necessary to select a specific storage bit, write information different from the information read from the specific storage bit, and then read and compare the information again, which takes time. In the following invention, information can be erased more efficiently.
[0015]
In the method for erasing information of a write-once memory according to the present invention, after writing single information to all storage bits of an erasure target area of the storage medium, writing other single information to the storage bits It is characterized by.
[0016]
It is preferable that the single information is information indicating "0" and the other single information is information indicating "1".
[0017]
Furthermore, it is preferable that the single information is information indicating “1” and the other single information is information indicating “0”.
[0018]
More specifically, first, information “0” is written to all the storage bits in a predetermined area. Here, assuming that the information (initial information) previously written in the storage bits of the predetermined area before use is “1”, the information is stored in the storage medium, and the storage bits in the predetermined area are stored. Since the information of "1" remaining in the information is completely rewritten to the information of "0", the erasure of the information is completed. However, when the initial information is “0”, the information of “1” in the storage bit is not erased, so that the information remains on the storage medium. Therefore, as the next step, by writing information of “1” to all the storage bits of the predetermined storage area, all of the information of “0” is rewritten to information of “1”, and the erasure of the information is stopped. It will end.
[0019]
Furthermore, information can be written in the reverse order. ADVANTAGE OF THE INVENTION According to this invention, even if what kind of information was previously written on the storage medium, the information can be efficiently erased without investigating it.
[0020]
The predetermined area is preferably the entire storage area of the storage medium, but may be a part.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method and an apparatus for erasing a storage medium according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a storage medium erasing device. FIG. 2 is a flowchart showing an erasing method executed by the storage medium erasing apparatus of FIG. FIG. 3 is a schematic diagram showing the storage bits in the storage medium in a matrix, and each square represents a storage bit.
[0022]
In FIG. 1, a CPU 1 (which may be, for example, a CPU of an electronic camera) is connected to a write-once memory 2 which is a storage medium via an interface 3, and stores a specific area of the write-once memory 2. Information of “0” or “1” can be written and read from the bit.
[0023]
A method for erasing a storage medium will be described. It is assumed that the target storage medium is known in advance to be a write-once memory. When the flash memory is also used for erasing, a step of detecting whether or not the memory is a write-once memory may be provided.
[0024]
In the case where the storage medium is a write-once memory, when data erasure is instructed for a part or all of the area (erasure target area) in the storage medium, in step S101 (first step) in FIG. , The CPU 1 reads the information of the first storage bit of the write-once memory 2, for example (it may be the last or intermediate as long as it is specified, but a plurality is preferable to increase the reliability of the judgment). Here, it is assumed that the information is 0 (see FIG. 3A). In response, in step S102 (second step), the CPU 1 writes (overwrites) information “1” as information different from the read information in the first storage bit.
[0025]
Further, in step S103 (third step), the CPU 1 reads the information of the first storage bit in which the information of “1” has been written, and in step S104 (fourth step), the written information “1” Compare with the read information. Here, if the written information and the information read therefrom are the same “1”, the write-once memory 2 has “0” information written in all storage bits before use. It can be seen that this is the case (see FIG. 3B). Therefore, in step S106, the CPU 1 writes the information “1” to all the areas to be erased (erasure target areas), thereby completing the information erasure. The write-once memory 2 from which information has been erased is in the state shown in FIG.
[0026]
On the other hand, if the written information “1” differs from the information “0” read therefrom in the comparison in step S104, the write-once memory 2 stores “1” in all storage bits before use. It can be seen that the information has been written (see FIG. 3C). Therefore, in step S105, the CPU 1 writes the information “0” to all the areas (areas to be erased), thereby completing the information erasure. The write-once memory 2 from which information has been erased is in the state shown in FIG.
[0027]
FIG. 4 is a flowchart illustrating a method of erasing a storage medium according to the second embodiment. First, in step S201, the CPU 1 writes information “0” to all of the storage bits in the erase target area (here, the entire storage area) of the write-once memory 2. Here, if the initial information previously written in the storage bits of the area to be erased before use is “1” (see FIG. 3C), they are rewritten to information “0”, Since the information is all rewritten to "0" (see FIG. 3B), the erasure of the information is completed at this point.
[0028]
However, if the initial information of “0” has been written in advance in the write-once memory 2 (see FIG. 3B), the information of “0” currently written is not erased, so that the information still remains. It will be. Therefore, in step S202, the CPU 1 performs an operation of rewriting all the storage bits of the erasure target area to the information of “1”, whereby all the initial information of “0” is rewritten to the information of “1”. Thus, the erasure of information is completed. According to the second embodiment, it is not necessary to read and compare information, so that information can be erased more quickly. As shown in parentheses in FIG. 4, information of “1” may be written first, and then information of “0” may be written.
[0029]
As described above, the present invention has been described with reference to the embodiments. However, the present invention should not be construed as being limited to the above embodiments, and it is needless to say that modifications and improvements can be made as appropriate. For example, it is not necessary to write information of “0” or “1” in all the storage bits, and only a predetermined area such as the center of the screen may be used. In the above description, information of “0” or “1” is written, but a specific erasure pattern (for example, 0101010101...) May be written uniformly. In this case, a storage bit that cannot be rewritten appears, but cannot be read at least as valid data.
[0030]
【The invention's effect】
According to the present invention, it is possible to provide a method of erasing a storage medium capable of efficiently making information stored in a storage medium such as a write-once memory unreadable.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a storage medium erasing device.
FIG. 2 is a flowchart illustrating a method of erasing a storage medium according to the first embodiment.
FIG. 3 is a schematic diagram showing storage bits in a storage medium in a matrix.
FIG. 4 is a flowchart illustrating a method of erasing a storage medium according to a second embodiment.
[Explanation of symbols]
1 CPU
2 Write-once memory 3 Interface

Claims (9)

A method for erasing information in a write-once memory, characterized by erasing information recorded in storage bits of an erasure target area by writing single information to all storage bits of an erasure target area of a storage medium. . 2. The method according to claim 1, further comprising the step of determining the single information. Determining the single information,
A first step of reading information of a predetermined storage bit,
A second step of writing information different from the information read in the first step into the storage bits read in the first step;
A third step of reading the information of the storage bits after the writing in the second step,
3. The write-once method according to claim 2, further comprising: a fourth step of determining whether the information read in said third step matches the information written in said second step. How to erase information from memory. When the information read in the third step matches the information written in the second step, the information written in the second step is determined as the single information,
If the information read in the third step does not match the information written in the second step, the information read in the first step is determined as the single information. The method for erasing information in a write-once memory according to claim 3. 5. The method according to claim 1, wherein the single information is information indicating "0" or "1". 2. The information erasing method for a write-once memory according to claim 1, wherein the single information is a specific erasing pattern. 2. The write-once method according to claim 1, wherein after writing single information to all storage bits of the erasure target area of the storage medium, another single information is written to the storage bits. How to erase information from memory. The method according to claim 7, wherein the single information is information indicating "0", and the other single information is information indicating "1". 8. The method according to claim 7, wherein the single information is information indicating "1", and the other single information is information indicating "0".

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