Flash EEPROM system
DC CAFCFirst Claim
1. A method of operating a memory system having an array of EEPROM cells divided into multiple non-overlapping sectors that individually contain a plurality of said cells sufficient to store multiple bytes of data and which are erasable together, comprising:
- (a) initially tagging a plurality of said multiple sectors to be erased,(b) subjecting the EEPROM cells of the tagged sectors in parallel to erase voltages while the remaining multiple sectors are not so subjected,(c) thereafter verifying whether individual ones of the tagged sectors have become erased,(d) clearing the tags from those sectors which are verified to have become erased while continuing to subject remaining tagged sectors to erase voltages, and(e) repeating operations (b) through (d) until the tags have been cleared from all of the initially tagged sectors, thereby to erase all the initially tagged sectors.
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Abstract
A system of Flash EEprom memory chips with controlling circuits serves as non-volatile memory such as that provided by magnetic disk drives. Improvements include selective multiple sector erase, in which any combinations of Flash sectors may be erased together. Selective sectors among the selected combination may also be de-selected during the erase operation. Another improvement is the ability to remap and replace defective cells with substitute cells. The remapping is performed automatically as soon as a defective cell is detected. When the number of defects in a Flash sector becomes large, the whole sector is remapped. Yet another improvement is the use of a write cache to reduce the number of writes to the Flash EEprom memory, thereby minimizing the stress to the device from undergoing too many write/erase cycling.
364 Citations
23 Claims
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1. A method of operating a memory system having an array of EEPROM cells divided into multiple non-overlapping sectors that individually contain a plurality of said cells sufficient to store multiple bytes of data and which are erasable together, comprising:
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(a) initially tagging a plurality of said multiple sectors to be erased, (b) subjecting the EEPROM cells of the tagged sectors in parallel to erase voltages while the remaining multiple sectors are not so subjected, (c) thereafter verifying whether individual ones of the tagged sectors have become erased, (d) clearing the tags from those sectors which are verified to have become erased while continuing to subject remaining tagged sectors to erase voltages, and (e) repeating operations (b) through (d) until the tags have been cleared from all of the initially tagged sectors, thereby to erase all the initially tagged sectors. - View Dependent Claims (2, 3, 4)
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5. A flash EEPROM system, comprising:
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a memory controller and system address bus, multiple sectors of flash EEPROM cells that are individually addressable through said address bus to be erased and which individually store multiple bytes of data, the cells of the individual sectors being erasable together when the individual sectors are addressed, a logic circuit configured to address and enable for erasure, in response to signals from the controller, any combination of a plurality of but less than all of said multiple sectors, and an erase circuit coupled to erase together all the enabled sectors without erasing others of the multiple sectors that are not so enabled. - View Dependent Claims (6, 7, 8, 9, 10)
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11. A flash EEPROM system, comprising:
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multiple sectors of flash EEPROM cells that are individually addressable for erasure and which individually store multiple bytes of data, the cells of the individual sectors being erasable together, a logic circuit configured to enable erasure of any one of multiple different combinations of a plurality of but less than all of said multiple sectors, and an erase circuit coupled to erase together all the enabled sectors of said any one combination without erasing others not in said any one combination. - View Dependent Claims (12, 13, 14, 15)
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16. A method of operating a memory system having an array of EEPROM cells divided into multiple non-overlapping sectors that individually contain a plurality of said cells sufficient to store multiple bytes of data and which are erasable together, comprising:
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(a) designating a combinations of a plurality of but less than all of said multiple sectors to be erased, (b) erasing the combination of sectors without erasing others of said multiple sectors, (c) after the combination of sectors has been erased, writing data in at least some of the erased combination of sectors, and (d) repeating the operations of (a) through (c) with another combinations of sectors. - View Dependent Claims (17, 18, 19, 20, 21, 22)
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23. A method of operating a memory system having an array of EEPROM cells divided into multiple non-overlapping sectors that individually contain a plurality of said cells sufficient to store multiple bytes of data and which are erasable together, comprising:
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(a) designating a combinations of any one of multiple different combinations of a plurality of but less than all of said multiple sectors to be erased, (b) erasing the combination of sectors without erasing others of said multiple sectors, and (c) after the combination of sectors has been erased, writing data in at least some of the erased combination of sectors.
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Specification