JPH0896588A - Semiconductor storage device - Google Patents

Abstract

PURPOSE: To prolong the device service life of a semiconductor storage device using nonvolatile memory elements having the limit of the number of rewriting. CONSTITUTION: A data storage area 11 is divided into independently rewritable plural storage blocks and rewriting is performed by writing data after rewriting data in an unassigned storage block and by changing a corresponding access objective block to a corresponding logical address. An unused block searching part 14 specifies an unused block to be used based on service situation information, an unused block list set at the time of an erasure initialization and an unused block chain similarily set at the time of the erasure. In the case where the unassigned block is not searched by the unused block searching part 14, an erasure managing part 15 secures the unused block by performing a physical erasure initialization including the saving and the changing of writing of effective data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor memory device using a nonvolatile memory element having a limited number of rewrites.

[0002]

2. Description of the Related Art Recently, as an external storage device for information equipment,
A storage device using a non-volatile semiconductor memory element such as a flash EEPROM is drawing attention. In particular, for portable information equipment, it is expected to be used as a non-volatile memory card or as an HDD substitute product because of its advantages of high impact resistance, small size, and low power consumption.

Generally, in EEPROM, block rewriting is required for rewriting. Therefore, rewriting involves the steps of reading the data of the block, erasing the block, correcting the necessary part of the data and writing it back.

With this rewriting operation, the EEPROM is
Has a drawback that the recording and erasing characteristics are deteriorated, and the number of times of rewriting is limited. By the way, in the external storage device of the information device, rewriting may occur frequently in a partial area, so in such a case,
There has been a problem that the device life is shortened by being limited by the number of times of rewriting of the element. For this problem, E
Conventionally, many techniques have been studied for avoiding the EPROM rewrite frequency limit systematically (all the way down) and artificially extending the device life.

The first of these is a method of combining with a volatile memory and using this volatile memory during operation to perform backup copying from the volatile memory to the non-volatile memory only when the power is turned off.

A second conventional example is Japanese Patent Laid-Open No. 63-
167498, JP-A 63-181190, JP-A 01
-277397, Japanese Patent Laid-Open No. 04-030399, the rewriting unit block is divided into a plurality of areas and sequentially written, assuming that a considerably small amount of data is repeatedly written as compared with the rewriting unit block. A method of reducing the number of times of erasure rewriting, and further, as a third conventional example, JP-A-02-023598, JP-A-02-053299,
JP-A-02-206097, JP-A-02-31089
6, JP-A-03-142794, JP-A-04-3012
As disclosed in 97, there is also a method of extending the life of the device by allocating a plurality of independently rewritable storage blocks to one data and distributing the rewriting.

[0007]

However, in the above-mentioned first conventional technique, since the volatile memory and the non-volatile memory have a double structure, the structure is complicated and it is disadvantageous in terms of cost.

Further, in the second and third prior arts, the apparent storage capacity is 1 / the number of regions or 1 / the number of blocks, and since the redundancy is high over all the regions, the blocks are rewritten less frequently. On the other hand, there is a problem that waste occurs.

[0009]

A device of the present invention is a semiconductor memory device using a non-volatile memory element having a limited number of rewrites, and is on a storage area composed of a non-volatile memory element having a limited number of rewrites. And a data storage unit comprising at least one independently erasable erase unit block composed of at least one independently writable storage block, and one of the storage blocks from the input logical address. A block selection unit for calculating physical address data to be designated, an unused block search unit for searching and selecting one of unused storage blocks in which no data is recorded from the data storage unit, and an initial erase of the storage block. And an erasure management unit that manages erasing, and at the time of rewriting, writes rewriting data to an unused storage block selected by the block searching unit. , And changes the selected target storage blocks in said block selector to unused storage blocks said selected.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a semiconductor memory device according to the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of a configuration example of a semiconductor memory device of the present invention.

The data storage section 11 is composed of a storage element having a limited number of rewrites, and is divided into a plurality of erase unit blocks which can be independently erased. Each erase unit block includes a plurality of storage blocks and a management information area.

The data control unit 12 inputs / outputs data to / from the outside, a data buffer function, and R for the data storage unit 11.
/ W control, in-block address control, etc. are managed.

The block selection unit 13 includes a data control unit 12
A single storage block is selected from the data storage unit 11 based on the logical address data supplied from the. The selection can be realized by referring to the address conversion table configured by the physical block number for the address data. The address designation for the data storage unit 11 at the time of reading / writing is performed by the block selection unit 13 based on the logical address data supplied from the data control unit 12, and is the physical number of the storage block to be read / written. Is combined with the in-block address, and the data control unit 12 outputs it to the data storage unit 11 as a physical address.

The unused block search unit 14 searches and selects one of the unused storage blocks in which no data is recorded from the data storage unit 11.

The erasure management unit 15 initializes the erasure of the storage area of the data storage unit 11 by saving the valid data from the data storage unit 11, erasing the valid data, and writing the valid data back to the data storage unit 11. .

When the storage block of the data storage unit 11 is rewritten, the unused block search unit 14 selects one of the unused storage blocks, writes the rewritten data into the selected unused storage block, and Selector 1
The address conversion table in 3 is changed so that the memory block in which the data has been newly written is selected corresponding to the logical address data. When the unused storage block cannot be found by the unused block search unit 14, the erase management unit 15 performs erase initialization to secure an unused storage block, and operates the unused block search unit 14 again. By doing so, an unused storage block used for rewriting is specified.

Next, three embodiments for identifying unused storage blocks to be used will be described.

In the first embodiment, an unused storage block is searched for by reading the usage status information area and determining it.

The usage status information can be composed of a flag group corresponding to the status of each storage block. The registered usage status information needs to always reflect the status of each storage block. That is, for information indicating whether or not it is used, when writing to a storage block, a corresponding flag indicating that it is used is set, and when erasing initialization of the storage block is performed. Must clear the corresponding flag.

Since the use status information may be erase-initialized at the same time as the corresponding storage block, it can be stored in the data storage section 11 constituted by a storage element having a limited number of rewrites. When the method of collectively erasing all storage blocks is adopted, they can be stored collectively. However, when erase initialization is performed for each erase unit block, each erase unit block must be at least erased. It is necessary to store the data in a partial area of the above, or to store the data in an area that can be independently erase-initialized in association with the erase initialization of the corresponding erase unit block and disperse it. In any case, the data can be further distributed and stored for each storage block.

FIG. 2 is a block diagram of the unused block search unit 14 in the above-mentioned first embodiment.

The used block search unit 14 outputs the storage circuit 21 for storing the physical block number of the storage block previously searched and designated, and the physical block number of the storage block to be determined to correspond to the use status information area. It can be configured by including a usage status reader 22 for reading out a portion to be used and a determiner 23 for judging the read usage status information.

The output block number of the usage status reader 22 is initialized to a number obtained by adding 1 to the storage block number indicated by the storage circuit 21 at the start of the search. Thereafter, this output block number is incremented until an unused storage block is detected or the final storage block is reached. By adopting such a configuration, the search time can be shortened by starting the determination as to whether or not the storage block is the unused one from the storage block next to the storage block previously designated for search.

The determiner 23 determines the read usage status information for each storage block. When an unused storage block is detected, the corresponding storage block number is notified to the data controller 12 and stored in the storage circuit 21. When the unused storage block cannot be detected when the inspection of the final storage block is completed, the data control unit 12 is notified that the unused storage block has not been detected.

When the unused storage block cannot be detected, the erase management unit 15 in FIG. 1 selects an erase unit block and performs erase initialization to secure the unused storage block. At that time, the management information such as the usage status information is also initialized, and the storage circuit 21 stores a number obtained by subtracting 1 from the storage block number to start the next search.

Next, in the second embodiment, when searching for an unused storage block and erasing and initializing it in the data storage unit 11, a list of address information of the unused storage block is created, and an address information area is created. This is done by reading the unused storage block addresses sequentially from the address information area.

As the address information, the newly secured unused storage block number is added to the list as the storage block is erased and initialized.

FIG. 3 is a block diagram showing a configuration example of the unused block search section 14 in the second embodiment as described above.

The unused block search unit 14 stores a memory circuit 31 for storing the previously designated position in the address information list on the address information area, a memory circuit 32 for storing the last position of the list, and the memory circuits 31 and 32. It can be configured by including a comparator 33 for comparing the contents of the above, and an address reader 34 for reading an unused storage block number stored at a position next to the position stored in the storage circuit 31.

When the contents of the storage circuits 31 and 32 match, the comparator 33 notifies the data control unit 12 that there is no unused storage block. If they do not match, the address reader 34 is operated to notify the data control unit 12 of the unused storage block number.

When the unused storage block cannot be detected, the erase management section 15 selects an erase unit block,
Erase initialization is performed to secure unused storage blocks. At that time, the number of the reserved unused storage block is added to the address information list, and the list end position data of the storage circuit 32 is updated.

Next, in the third embodiment, when searching for an unused storage block, when erasing and initializing the data storage unit 11, the unused storage block to be used next for each unused storage block. This is done by creating connection information indicating a block, storing it in the connection information area, and sequentially reading unused storage block addresses from the connection information area.

The connection information can be stored in the data storage unit 11, like the usage information. Since it is necessary to perform erase initialization at the same time as the corresponding memory block, it is possible to store all memory blocks in a batch when they are erased collectively, but when performing erase initialization for each erase unit block , At least for each erase unit block, stored in a partial area of each erase unit block, or stored in an area that can be independently erase-initialized in association with erase initialization of the corresponding erase-unit block and distributed. There is a need. In any case, the data can be further distributed and stored for each storage block.

Further, the connection chain of unused storage blocks is connected when erasing all storage blocks at once, and is connected for each erasing unit block when erasing initialization is performed for each erasing unit block. . For the last unused storage block of the unused storage block chain, information indicating the last of the chain is stored in the connection information area.

FIG. 4 shows a block diagram of a configuration example of the unused block search unit 14 in the above-mentioned third embodiment.

The unused block search unit 14 stores the unused memory block number designated last time in the memory circuit 41.
And a connection information reader 42 for reading out the connection information corresponding to the storage block number stored in the storage circuit 41.
And a determination device 43 for determining the read connection information.

The judging device 43 judges that the read connection information is
When it is indicated that it is at the end of the unused storage block chain, in the next search, the unused storage block number is read and output from the storage circuit 44 which is the FIFO memory. If the storage circuit 44 is empty, the data control unit 12 is notified that the unused storage block could not be detected, and if the unused storage block number is indicated, the corresponding unused storage block number is set. The data control unit 12 is notified.

When the unused storage block cannot be detected, the erase management unit 15 selects an erase unit block,
Erase initialization is performed to secure unused storage blocks. At that time, the connection information is set to construct an unused storage block chain, and the number of the first storage block of the unused storage block chain is registered in the storage circuit 44.

Next, two types of embodiments relating to the setting of the range of the erase initialization of the memory block to secure the unused memory block will be described.

The first one (fourth embodiment of the present invention) performs erase initialization of memory blocks in a batch of all memory blocks.

In this case, since the data storage unit 11 can be used as one area, various processes are simplified. Further, it becomes possible to average the erase operation of the memory elements. In reality, the temporary memory area for saving valid data may be limited in size and may be performed for each erase unit block depending on the physical configuration of the storage element itself.

In the second one (fifth embodiment of the present invention), erase initialization of a memory block is sequentially performed one block at a time for a plurality of erase unit blocks.

In this case, an erase block selecting section for selecting an erase unit block to be erased is required. The erase block selection unit may be configured by, for example, a counter that performs an increment operation for each erase operation and is initialized to point to the first erase unit block after pointing to the final erase unit block. By sequentially selecting the erase unit blocks in this manner, it becomes possible to average the erase operation of the memory elements. In addition, the erase initialization waiting time can be dispersed by dividing the erase initialization operation.

In both the fourth embodiment and the fifth embodiment described above, if an unused memory block cannot be obtained even if the erase unit block is erase-initialized, the erase unit block is not erased. It is also possible to set the process. For example, the erase unit block is provided with a flag information area indicating whether or not an unused storage block can be secured by performing erase initialization, and when rewriting, a storage block in which old data that is out of the access target is stored It is included. A flag in the information area of the erase unit block is set. In this case, at the time of erasing, it is possible to determine whether or not to erase by referring to the flag information area of the corresponding erase unit block.

Prior to erasing, valid data must be saved in the temporary memory. As a method for determining whether the storage block contains valid data,
For example, it is possible to use an address conversion table. That is, the determination can be made by utilizing that the storage block whose physical storage block number is registered in the address conversion table contains valid data. However, in this method, it is necessary to search and compare the entire address conversion table in order to determine whether or not the target storage block contains valid data.

As another method, for each storage block, a validity information area for registering information indicating whether or not valid data is included is provided and combined with the use status information in the first embodiment. You can make a decision. In other words, at the time of rewriting, if old data is held and there is invalid data, setting a flag at the corresponding position in the validity information area indicates that it is used in the usage status information. It is possible to determine that a storage block that has been stored and whose validity information does not indicate that the data is not valid contains valid data.

Next, three embodiments relating to the timing of starting to reserve an unused storage block will be described.

In the first one (sixth embodiment of the present invention), an unused storage block used at the time of rewriting is searched at the start of rewriting.

The second one (seventh embodiment of the present invention) is configured to operate the unused block search unit 14 at the end of rewriting to secure an unused block to be used at the next rewriting. . As a result, an unused storage block can be prepared before the next rewriting operation, and the waiting time for securing the unused storage block at the time of rewriting can be apparently eliminated. Especially when erasing storage blocks is processed in the background,
Considered to be effective. However, a storage circuit for storing the number of an unused storage block to be used next time is required.

The third one (eighth embodiment of the present invention) enables rewriting of a plurality of storage blocks with a preset number of storage blocks as an upper limit, and the reserved unused block is preset. When the number of storage blocks is reduced, the unused block search unit 14 is operated. As a result, the preset number of blocks can be continuously rewritten, and the waiting time for reserving unused storage blocks in the rewriting operation is further reduced. A FIFO memory or the like for storing the numbers of unused storage blocks is required.

Further, it may be constructed in combination with the unused block searching unit 14 in the above-mentioned second embodiment of the present invention. That is, when the unused memory block is stored, the memory is also used as the address information list used by the unused block search unit 14, and when the unused memory block is secured by the erase initialization, the preset number of blocks is reached. Up to one erase unit block may be erase-initialized and registered in the address information list.

[0053]

In the semiconductor memory device according to the present invention, the number of physical erases of the memory element can be reduced and the number of erases can be averaged. Therefore, even in a semiconductor memory device constructed using a non-volatile memory element having a limited number of rewrites, it is possible to avoid the relaxation of the element rewrite and relax the life of the device. Further, the semiconductor memory device according to the present invention can be easily realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a configuration example of a semiconductor memory device of the present invention.

FIG. 2 is a block diagram of a configuration example of an unused block search unit in the first exemplary embodiment of the present invention.

FIG. 3 is a block diagram of a configuration example of an unused block search unit according to a second embodiment of the present invention.

FIG. 4 is a block diagram of a configuration example of an unused block search unit in the third exemplary embodiment of the present invention.

[Explanation of symbols]

 11 Data Storage Section 12 Data Control Section 13 Block Selection Section 14 Unused Block Search Section 15 Erase Management Section 21 Storage Circuit 22 Usage Status Reader 23 Judgment Device 31 Storage Circuit 32 Storage Circuit 33 Comparator 34 Address Reader 41 Storage Circuit 42 Connection information reader 43 Judgment device 44 Storage circuit

Claims (9)

[Claims] 1. A semiconductor memory device using a non-volatile memory element having a limited number of times of rewriting, wherein at least one independently writable in a storage area composed of the non-volatile memory element having a limited number of times of rewriting. Data storage unit including at least one independently erasable erase unit block composed of various storage blocks, and block selection for calculating physical address data designating one of the storage blocks from an input logical address A storage unit, an unused block search unit that searches and selects one of the unused storage blocks in which no data is recorded from the data storage unit, and an erase management unit that manages erase initialization of the storage block. Then, at the time of rewriting, the rewriting data is written in the unused storage block selected by the block searching unit and selected by the block selecting unit. The semiconductor memory device characterized by changing the target storage blocks in the unused storage blocks said selected. 2. A usage status information area for storing information indicating whether or not it is already used is provided for each storage block, and the unused block search unit reads the usage status information area, 2. The semiconductor memory device according to claim 1, wherein an unused storage block is searched from a storage block subsequent to the unused storage block designated by the search. 3. When erasing and initializing the data storage unit,
Create a list of address information of unused storage blocks,
The unused block search unit has an address information area for storing, and the unused block search unit reads out an unused storage block registered next to the unused storage block previously searched and specified from the address information area, and The semiconductor memory device according to claim 1, wherein a used memory block is specified. 4. When erasing and initializing the data storage unit,
For each unused storage block, a connection information area for creating and storing connection information pointing to an unused storage block to be used next is provided, and the unused block search unit is provided with the previously specified unspecified 2. The semiconductor memory device according to claim 1, wherein connection information corresponding to a used storage block is read from the connection information area and an unused storage block to be used is specified. 5. The erasure management unit, when the unused block search unit cannot find an unused storage block, saves valid data for all storage blocks and then erases the effective data. 2. The semiconductor memory device according to claim 1, wherein an unused memory block is secured by rewriting. 6. The data storage unit is divided into a plurality of erase unit blocks including at least one storage block, and the erase management unit includes an erase block selection unit that sequentially selects the erase unit blocks, When the unused block search unit cannot find an unused storage block, the valid data is saved to the erase unit block selected by the erase block selection unit, then erased, and the valid data is written back. The semiconductor memory device according to claim 1, wherein an unused memory block is secured thereby. 7. The semiconductor memory device according to claim 1, wherein an unused block search unit is operated at the start of rewriting to secure an unused memory block to be used. 8. The semiconductor memory device according to claim 1, wherein an unused block search unit is operated at the end of rewriting to secure an unused storage block to be used at the next rewriting. 9. An unused block search unit that enables rewriting of a plurality of storage blocks with a preset number of storage blocks as an upper limit, and when the number of reserved unused blocks falls below the preset number of storage blocks. 2. The semiconductor memory device according to claim 1, wherein the semiconductor memory device is operated to secure at least an unused memory block by the preset number of memory blocks.