JPH11297082A - Method of rewriting data in flash memory and semiconductor memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need of a memory medium for the counts of cumulative number of erasures at each sector to enable the simplification of the software by eliminating the need for counting the cumulative number of erasures at each sector of a flash memory. SOLUTION: The data rewriting method comprises providing a unique word region 3 for previously storing a plurality of unique words showing the sector being in an erase state in a flash memory, writing the unique words on data areas at unique word in-sector addresses in a sector when being in the erase state, collating, to rewrite sector data on data areas at the unique word in-sector addresses of a sector to be a candidate for the data rewriting sector with the latest unique word stored in the unique word region 3, using a collator 7, selecting this candidate sector as a data rewriting sector when the collated data agree and taking other sector as a candidate for the rewriting sector when the collated data do not agree, using the collator 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of rewriting data in a flash memory which can be accessed in units of sectors, in which a unit of writing data in a sector is different from an erasing unit, and in which the writing unit is smaller than the erasing unit. The present invention relates to a semiconductor memory device using a flash memory.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram of a conventional semiconductor memory device using a flash memory. In FIG. 3, 1
01 to 10N are sectors divided into the same size as the erase size of the flash memory.
N is a sector in which data in the sector can be read and written randomly for each address in the sector. Numeral 11 denotes a sector area composed of a plurality of sectors 101 to 10N. Numeral 12 denotes a sector control unit. A pointer managed by the sector control unit 12 can freely move each sector address and an address in a sector to read, write, erase, etc. Input and output with the memory can be performed. 1
Reference numeral 3 denotes a bus, 14 denotes a memory control unit for giving instructions to the sector control unit 12 to control a memory storage / reproduction operation to the flash memory, and 161 to 16N exist one by one corresponding to each sector. A counter 15 for counting the number of cumulative erasures is a counter storage unit that includes a plurality of counters 161 to 16N and stores respective count values.

In this conventional semiconductor memory device, a sector area 11 is composed of a flash memory, a memory control unit 14 gives an instruction to a sector control unit 12, and the sector control unit 12 reads the sectors 101 to 10N according to the instruction. , Writing, and erasing. Further, the counter storage unit 15 for storing the count values of the counters 161 to 16N, that is, the cumulative erase count of each sector, is provided in a storage medium different from the flash memory.

[0004] A data rewriting operation of the flash memory in the conventional semiconductor memory device will be described. Here, the rewriting source sector is defined as sector 101, and sector 10 is rewritten.
It is assumed that part of the arbitrary data in 1 is rewritten. The memory control unit 14 determines, for example, sector 1 as a rewrite destination sector.
02 as a candidate, the counter 162 of the counter storage unit 15
, The accumulated erase count of the sector 102 is read. Subsequently, the memory control unit 14 compares the maximum number of erases specified by the flash memory with the value of the counter 162, and
If the value of 2 is the cumulative number of erasures equal to or greater than the maximum number of erasures, the candidate for the write destination sector is changed to a sector other than the sector 102, and the above-described readout procedure of the counter storage unit 15 is repeated.

If the value of the counter 162 is smaller than the maximum number of times of erasure, the memory control unit 14 relatively manages addresses in the sectors of the rewrite source sector 101 and the rewrite destination sector 102, and performs data rewrite. Until the address in the sector of the rewriting destination sector 102 is reached,
Via the bus 13, the sector controller 12 is instructed to read data of a unit smaller than the size of the entire sector from the rewrite source sector 101. The sector control unit 12 reads data from the rewrite source sector 101 and sends the data to the memory control unit 14 via the bus 13. Memory control unit 14
Instructs the sector control unit 12 to write data to the rewrite destination sector 102 via the bus 13. The above procedure is repeated up to the intra-sector address of the rewrite destination sector 102 for rewriting data.

Thereafter, when the memory control unit 14 recognizes the address in the sector of the rewrite destination sector 102 to be rewritten, the memory control unit 14 instructs the sector control unit 12 to write the rewrite data to the rewrite destination sector 102 via the bus 13. Thereafter, the memory control unit 14 moves the data after the address in the sector where the rewriting of the rewriting source sector 101 is performed to the rewriting destination sector 102. This is repeated up to the address in the last sector of the rewrite source sector 101.

After that, the memory control unit 14 instructs the sector control unit 12 to erase the rewrite source sector 101 via the bus 13. After the sector control unit 12 erases the rewrite source sector 101, the memory control unit 14
Of the counter 161 of the cumulative number of erases corresponding to only the rewrite source sector 101 is counted.

[0008]

In the above conventional example, the cumulative erase count of each sector is counted, and when rewriting data in a sector, the count value of the cumulative erase count and the maximum value of the cumulative erase count are rewritten in addition to writing the rewrite data. Since the number of erasures needs to be compared, the cumulative number of erasures since the start of using the flash memory must be maintained accurately both when the flash memory is in use and when it is not in use, and the count value itself is flashed. Since the memory cannot be stored in the memory, a storage medium different from the flash memory is required as the counter storage unit 15, and software is very complicated in order to manage the same number of counters 161 to 16N as the number of sectors. There was a problem of control.

An object of the present invention is to eliminate the need to count the cumulative erase count of each sector, and thus eliminate the need for a storage medium separate from the flash memory for storing the count value of the cumulative erase count of each sector. It is therefore an object of the present invention to provide a flash memory data rewriting method and a semiconductor memory device that can simplify software.

[0010]

According to a first aspect of the present invention, there is provided a data rewriting method for a flash memory which reads data of a rewriting source sector among a plurality of sectors constituting a flash memory and stores the read data in a plurality of sectors. A data rewriting method for a flash memory for writing data to a rewriting destination sector selected from the above and erasing data in a rewriting source sector, wherein a specific data area in which a plurality of specific data indicating that a sector is in an erased state is previously stored is flashed A specific data write area where specific data is written in each sector is set in advance in the memory, and a sector in which the latest specific data is written in the specific data write area is selected as a rewrite destination sector. After erasing the specified data, the specific data And writes a selected one from a plurality of specific data stored in the band as the next specified data.

According to this data rewriting method for a flash memory, a specific data area in which a plurality of specific data indicating that a sector is in an erased state is provided in the flash memory in advance, and the specific data area for writing the specific data to each sector is provided. Since the write area is set in advance, the sector in which the latest specific data has been written in the specific data write area is writable, and the sector is selected as a rewrite destination sector. Eliminates the need to count the cumulative erase count for each sector, thus eliminating the need for a separate storage medium from the flash memory to store the cumulative erase count count for each sector, further simplifying software become.

A flash memory data rewriting method according to a second aspect of the present invention is the flash memory data rewriting method according to the first aspect, wherein the plurality of specific data stored in the specific data area of the flash memory is a specific data corresponding to each sector. It consists of data. in this way,
By using the specific data corresponding to each sector, the reliability of determining whether or not each sector is writable is increased.

According to a third aspect of the present invention, in the semiconductor memory device, a plurality of sectors in which specific data write areas for writing specific data indicating an erased state are set in each area and a plurality of specific data are stored in advance. A flash memory having a specific data area; a sector control unit for reading, writing, and erasing data from and to the flash memory; and reading data from a rewrite source sector among the plurality of sectors and transferring the read data to a plurality of sectors. When writing to a rewrite destination sector selected from among the above, a collation unit that collates data in a specific data write area of a sector that is a candidate for a rewrite destination sector with the latest specific data stored in the specific data area. To the sector control unit, and when the collation result by the collation unit matches, the A memory control unit for selecting a candidate sector as a rewriting destination sector, and when the collation result by the collating unit does not match, a memory control unit for selecting another sector as a candidate for the rewriting destination sector; In the area, one selected from a plurality of specific data stored in the specific data area is written as the next specific data.

According to this configuration, the specific data area for storing a plurality of specific data indicating that the sector is in the erased state is provided in the flash memory, and the specific data write area for writing the specific data in each sector is set in advance. Therefore, when rewriting data in a sector, the sector in which the latest specific data has been written in the specific data write area is writable, and that sector is selected as the rewrite destination sector. This eliminates the need for counting the cumulative erase count of each sector as in the related art, and thus eliminates the need for a storage medium separate from the flash memory for storing the count value of the cumulative erase count of each sector. Software can be simplified.

According to a fourth aspect of the present invention, in the semiconductor memory device according to the third aspect, the plurality of specific data stored in the specific data area of the flash memory comprises specific data corresponding to each sector. And As described above, by using the specific data corresponding to each sector, the reliability of determining whether each sector is writable is improved.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a semiconductor memory device according to an embodiment of the present invention. In FIG. 1, reference numerals 111 to 11N denote sectors divided into a size equal to the erase size of the flash memory, and sectors 111 to 11N are sectors in which data in the sector can be read and written randomly for each address in the sector. . 2 is a sector area composed of a plurality of sectors 111 to 11N, 3 is a unique word area in which a plurality of unique words are stored, and is readable, and 4 is a pointer to be managed which moves freely between each sector address and an address in a sector.
A sector controller 5 capable of reading, writing, and erasing controls the continuity between the respective sectors of the flash memory (controls such that a plurality of sectors are continuously chained while being aware of the order), and has already been written (written). impossible),
A memory control unit that can temporarily hold information on the status of each sector such as erased (writable), 6 is a bus connecting the sector control unit 4 and the memory control unit 5, and 7 is data from the memory control unit 5. This is a collating unit that verifies the collation and returns the collation result.

In the semiconductor memory device of the present embodiment, a part which has been conventionally used as a sector area is used for a unique word area 3, and the unique word area 3 and the sector area 2 are constituted by flash memories. The unique word area 3 previously stores a plurality of unique words (specific data) indicating that the sector is in the erased state. Then, when each sector enters the erased state,
One selected from the plurality of unique words in the unique word area 3 is written as the next unique word in the data area (specific data write area) of the unique word sector address (specific sector address),
A different unique word is selected and written every time the erase state is entered.

A collation unit 7 is provided, and when rewriting data of a sector, the data of the data area of the address within the unique word sector of the sector which is a candidate for the rewriting destination sector and the unique word area 3 The stored latest unique word (unique word indicating that it is currently in the erased state) is collated. The memory control unit 5 selects a sector as a rewrite destination sector when the collation result of the collation unit 7 matches, and rewrites another sector when the collation result of the collation unit 7 does not match. It is set as a candidate for the destination sector.

The data rewriting method in the sector area 2 of the semiconductor memory device according to the present embodiment configured as described above,
That is, the data rewriting method of the flash memory will be further described with reference to the flowchart shown in FIG. Here, it is assumed that a plurality of data has already been written in the sector 111 arranged in the sector area 2. The rewriting source sector is defined as a sector 111, and the sector 111
It is assumed that a part of the data is rewritten.

First, the memory control unit 5, for example,
12 is selected as a candidate for the rewriting destination sector (step S1). Next, in step S2, the memory control unit 5
Is transmitted to the sector control unit 4 via the bus 6 and
An instruction is issued to read a unique word (hereinafter referred to as “written unique word”) written in the data area of the 12 unique word sector addresses. The sector control unit 4 reads out the written unique word from the data area of the address within the unique word sector of the rewrite destination sector 112 and sends it to the memory control unit 5 through the bus 6. After that, the memory control unit 5 transfers the read written unique word to the collation unit 7.

Next, in step S3, the memory control unit 5 instructs the sector control unit 4 via the bus 6 to read the latest unique word from the unique word area 3. The sector control unit 4 reads out the latest unique word from the unique word area 3 and sends it to the memory control unit 5 via the bus 6. After that, the memory control unit 5 transfers the latest unique word to the matching unit 7.

Next, in step S4, the collating unit 7
Compares the written unique word with the latest unique word, and returns a result of the comparison to the memory control unit 5. If the collation results do not match, the memory control unit 5 determines that the sector 112 is not writable, returns to step S1, selects a sector other than the sector 112 as a candidate for a rewrite destination sector, and similarly proceeds to step S1. In S4, the process is repeated until the collation result between the written unique word and the latest unique word matches.

The case where the collation results match in step S4 will be described. Here, when the sector 112 is set as a candidate for the rewrite destination sector, the matching results match, and the memory control unit 5 determines that the sector 112 is a writable sector,
It is assumed that the sector is selected as a rewrite destination sector. Next, the memory control unit 5 relatively manages the intra-sector addresses of the rewrite source sector 111 and the rewrite destination sector 112, and controls the sector control unit through the bus 6 until the address in the sector at which the rewrite destination sector 112 is rewritten is reached. Instruct 4 to read data of a unit smaller than the size of the entire sector from the rewrite source sector 111. The sector control unit 4 reads data from the rewrite source sector 111 and sends the data to the memory control unit 5 via the bus 6. The memory control unit 5 instructs the sector control unit 4 to write to the rewrite destination sector 112 via the bus 6. The above procedure is performed in the rewriting destination sector 1
The repetition is repeated up to the address in the sector where the rewriting is performed (step S5, S6, S8, S9, S10).

Then, in step S6, the memory control unit 5
Recognizes the address in the sector where the rewrite destination sector 112 is to be rewritten, and instructs the sector control unit 4 via the bus 6 to write the rewrite data to the rewrite destination sector 112. Thereafter, the memory control unit 5 sets the rewrite source sector 111
The data after the address in the sector where the rewriting is performed is moved to the rewriting destination sector 112. This is repeated until the address within the last sector of the rewrite source sector 111 or until all the remaining data is moved (steps S5 and S5).
6, repetition route of S7, S8, S9, S10).
Since each sector has a sufficiently larger capacity than the data to be normally rewritten, data to be actually rewritten is prepared in step S7 while most of the data movement is not changed.

Thereafter, in step S11, the memory control unit 5 instructs the sector control unit 4 to erase the rewrite source sector 111 through the bus 6. The sector control unit 4 erases data in the rewrite source sector 111. Next, in step S12, the memory control unit 5 instructs the sector control unit 4 via the bus 6 to read the next unique word corresponding to the current data rewriting from the unique word area 3, and The read unique word is written into the data area of the unique word address within the sector 111 (step S13).

As described above, according to the present embodiment, a unique word area 3 for previously storing a plurality of unique words indicating that a sector is in an erased state is provided in a flash memory, and a unique word is written in each sector. Since the data area of the word sector address is set in advance, when rewriting data in the sector, the sector in which the latest unique word has been written in the data area of the unique word sector address can be written. Yes, the sector is selected as a rewrite destination sector, so that it is not necessary to count the cumulative erase count of each sector as in the related art. Therefore, the count value of the cumulative erase count of each sector is stored. This eliminates the need for a storage medium separate from the flash memory for It becomes possible.

By storing a unique word corresponding to each sector in the unique word area 3 and writing a unique word corresponding to each sector, whether each sector is writable or not is determined. The reliability of the judgment increases. Although the collating unit 7 is provided, the collating unit 7 has a smaller circuit size than the conventional counter storage unit 15 of FIG. 3 and can reduce the size of the entire semiconductor memory device.

In the semiconductor memory device of the present embodiment, digital data, particularly audio digital data, is suitable as data to be written in each of the sectors 111 to 11N of the sector area 2.

[0029]

As described above, according to the present invention, a specific data area for previously storing a plurality of specific data indicating that a sector is in an erased state is provided in a flash memory, and specific data is written in each sector. Since the data write area is set in advance, when data in the sector is rewritten, the sector in which the latest specific data has been written in the specific data write area can be written, and that sector is set as the rewrite destination sector. The selection eliminates the necessity of counting the cumulative erase count of each sector as in the related art, and is therefore different from the flash memory for storing the count value of the cumulative erase count of each sector. No media is required, and software can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram of a semiconductor memory device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a data rewriting method according to the embodiment of the present invention.

FIG. 3 is a block diagram of a conventional semiconductor memory device.

[Explanation of symbols]

 111-11N Sector 2 Sector area 3 Unique word area 4 Sector control unit 5 Memory control unit 6 Bus 7 Collation unit

Claims (4)

[Claims] 1. A method for reading data of a rewrite source sector among a plurality of sectors constituting a flash memory, writing the read data to a rewrite destination sector selected from the plurality of sectors, and rewriting data in the rewrite source sector. A data rewriting method for a flash memory for erasing data, wherein a specific data area in which a plurality of specific data indicating that the sector is in an erased state is stored in advance in the flash memory, and the specific data is written to each sector A specific data write area is set in advance, a sector in which the latest specific data is written in the specific data write area is selected as the rewrite destination sector, and the data in the rewrite source sector is erased before the rewrite. Stored in the specific data area in the specific data write area of the original sector Serial plurality of data rewriting method of a flash memory and writes the selected one from among the specified data as the next specified data. 2. The flash memory data rewriting method according to claim 1, wherein the plurality of specific data stored in the specific data area of the flash memory includes specific data corresponding to each sector. 3. A plurality of sectors in which a specific data write area for writing specific data indicating an erased state in each area is set in advance, and a specific data area in which a plurality of the specific data are stored in advance. A flash memory; a sector control unit for reading, writing, and erasing data from and to the flash memory; reading data of a rewrite source sector among the plurality of sectors; and selecting the read data from the plurality of sectors A collating unit for collating the data of the specific data write area of the candidate sector for the rewrite destination sector with the latest specific data stored in the specific data area when writing to the rewritten destination sector And issues an instruction to the sector control unit, and when the matching result by the matching unit matches, A memory control unit for selecting a sector as a candidate for a rewrite destination sector as the rewrite destination sector, and when the collation result by the collation unit does not match, a memory control unit for making another sector a candidate for the rewrite destination sector; A semiconductor memory device in which one selected from the plurality of specific data stored in the specific data area is written as the next specific data in the specific data write area of the rewrite source sector. 4. The semiconductor memory device according to claim 3, wherein the plurality of specific data stored in the specific data area of the flash memory comprises specific data corresponding to each sector.