US 5,719,808 A · Flash EEPROM system

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.

Claims23

Dependent claims

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.

2 more elements

Dependencies are inferred from the claim text.

Flash EEPROM system

Life of this patent

Flash EEPROM system

Life of this patent

Abstract

Claims23