Multi-state Flash EEprom system on a card that includes defective cell substitution
First Claim
1. A memory card connectable to a computer system, comprising:
- an array of Electrically Erasable and Programmable Read Only Memory ("EEPROM") cells partitioned into a plurality of flash sectors, the cells of the array being individually programmable into more than two states in order to store more than one bit of data per cell;
each flash sector being a group of cells that are erasable together as a unit, and having a portion thereof reserved as redundant cells; and
a memory controller for controlling operations of the EEPROM cells;
error detection means within said memory controller for detecting any defective cells within the array;
defect pointers, each generated by said memory controller for linking a detected defective cell'"'"'s address to that of a corresponding redundant cell substituting for the defective cell, said defect pointers being stored within the array; and
defective cell substituting means within said memory controller and responsive to said defect pointers for substituting said detected defective cell with said corresponding redundant cells.
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Accused Products
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.
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Citations
18 Claims
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1. A memory card connectable to a computer system, comprising:
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an array of Electrically Erasable and Programmable Read Only Memory ("EEPROM") cells partitioned into a plurality of flash sectors, the cells of the array being individually programmable into more than two states in order to store more than one bit of data per cell; each flash sector being a group of cells that are erasable together as a unit, and having a portion thereof reserved as redundant cells; and a memory controller for controlling operations of the EEPROM cells; error detection means within said memory controller for detecting any defective cells within the array; defect pointers, each generated by said memory controller for linking a detected defective cell'"'"'s address to that of a corresponding redundant cell substituting for the defective cell, said defect pointers being stored within the array; and defective cell substituting means within said memory controller and responsive to said defect pointers for substituting said detected defective cell with said corresponding redundant cells. - View Dependent Claims (2, 3, 4)
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5. A memory card connectable to a computer system, said memory card comprising:
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an array of non-volatile floating gate memory cells partitioned into a plurality of sectors that individually include a distinct group of said array of memory cells that are erasable together as a unit, the individual sectors including a user data portion and a spare portion of the group of memory cells, the cells of the array being individually programmable into more than two states in order to store more than one bit of data per cell, a memory controller for controlling operation of the memory cell array and interfacing the memory cell array with the computer system, means within said memory controller for identifying defective cells within the user data portion of individual ones of said plurality of sectors, and means including said memory controller and responsive to detection of a defective cell within the user data portion of one of said plurality of sectors for substituting therefore a corresponding redundant cell within the spare portion of said one of said plurality of sectors. - View Dependent Claims (6, 7, 8)
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9. A method of operating a computer system including a processor and a memory system, wherein the memory system includes an array of non-volatile floating gate memory cells partitioned into a plurality of sectors that individually include a distinct group of said array of memory cells that are erasable together as a unit, comprising:
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providing said memory array and a memory controller within a card that is removably connectable to the computer system, said controller being connectable to said processor for controlling operation of the array when the card is connected to the computer system, programming the individual cells of the array into one of more than two programmable states in order to store more than one bit of data per cell, reserving a portion of the memory cells within the individual sectors as spare cells, remaining cells of the individual sectors being designated for storing data, enabling the controller to detect when a cell within the data portion of a sector becomes defective, causing the controller to store an address of such a detected defective cell, and thereafter causing the controller to substitute for the defective cell a redundant cell from the spare cells of the sector in which the defective cell is detected. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18)
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Specification