Patent ID: 6172915
Filing Date: 2001-01-09
Classification: G11C

Abstract:
A unified erase method used in an array of flash EEPROM memory cells arranged in a plurality of sectors for performing either a single-sector, multiple-sector, or all-sector erasing operation with a reduced amount of total erase time, said erase method comprising the steps of:turning an erase-signal ON in only certain ones of said plurality of sectors which are required to be erased;programming initially all bytes in said certain ones of said plurality of sectors which are required to be erased;setting current address in said certain ones of said plurality of sectors which are required to be erased to a first address;(a) determining whether a first sector of said plurality of sectors has its erase-on signal turned OFF;(b) bypassing said first sector if said erase-on signal is turned OFF and proceeding to a second sector of said plurality of sectors;(c) determining whether the current address has been erased if said erase-on signal is not turned OFF;(d) proceeding to the second sector of said plurality of sectors if the current address has not been erased and storing in an address register the current address;(e) determining whether the current address is the last address of said first sector if the current address has been erased;(f) increasing the current address by one if the current address is not the last address and repeating steps (c)-(e);(g) turning OFF said erase-on signal if the current address is the last address and proceeding to the second sector of said plurality of sectors;repeating steps (a) through (g) for the remaining sectors of said plurality of sectors except for a last sector;determining whether the last sector of said plurality of sectors has its erase-on signal turned OFF;determining whether the erase-on signal for all sectors of said plurality of sectors are turned OFF if the last sector has its erase-on signal turned OFF;(i) determining whether the current address of the last sector has been turned OFF if said erase-on signal is not turned OFF;(j) storing current address in an address register if the current address is not erased;(k) determining whether the current address is a last address of said last sector if the current address has been erased;increasing the current address by one if the current address is not the last address and repeating steps (i) through (k);turning OFF said erase-on signal if the current address is the last address;applying an erase pulse to all bytes in all sectors simultaneously in which the erase-on signals have not been turned OFF if the current address of the last sector has not been erased or if the erase-on signal for all sectors have not been turned OFF and repeating steps (a) through (k); andterminating the erasing operation when the erase-on signal has been turned OFF in all sectors of said plurality of sectors.