Smart erase algorithm with secure scheme for flash EPROMs
AssigneeTexas Instruments Incorporated
InventorsTim M. Coffman, Sung-Wei Lin, T. Damodar Reddy
Life of this patent
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Abstract
A method for erasing blocks of a non-volatile memory includes detecting whether a block is in at least one of an erased state or a state secured from erasure; then setting a flag register at a first level for each block detected to be in at least one of an erased state or a state secured from erasure or at a second level for each block not so detected; then selecting for erasure blocks that have their respective flags set at the second level; and then erasing the selected blocks.
Claims5
A non-volatile memory fabricated on a silicon substrate, the memory having blocks of memory cells, means for programming the cells, means for erasing the blocks, means for securing the blocks against erasure, means for detecting whether a block is in an erased state or in a state secured from erasure, and a memory controller for controlling the programming, erasing, securing, and detecting means, the memory further comprising:
- (a) a mark latch for each block, each mark latch responsive to signals from the means for detecting, for generating a MARK signal indicating if its respective block has been erased, each mark latch comprising:
- first and second NOR gates responsive to signals from the means for detecting, the output of the first NOR gate connected to an input of the second NOR gate, and the output of the second NOR gate connected to an input of the first NOR gate;
- and
- (b) a secure latch for each block, each secure latch responsive to signals from the means for detecting, for generating a SKIPDAT signal indicating if its respective block has been secured against erasure, each secure latch comprising:
- first and second NAND gates responsive to signals from the means for detecting, the output of the first NAND gate connected to an input of the second NAND gate, and the output of the second NAND gate connected to an input of the first NAND gate.
Dependencies are inferred from the claim text.