introduction to flash memory

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1、IntroductiontoFlashmemoryIvanChenTopicsFlashmemoryoverviewNorflashandubootdriverNandflashandubootdriverSPIflashandubootdriverMulti-mediacard(MMC)Securedigitalcards(SD)FlashmemoryoverviewFlashmemoryisanon-volatilecomputerstoragechipthatcanbeelectricallyerasedandreprogrammed.It’spr

2、imarilyusedinmemorycards,USBflashdrivers,MP3playersandsolid-statedrivesforgeneralstorageandtransferofdatabetweencomputersandotherdigitalproducts.Flashmemoryoverview(History)Flashmemory(bothNORandNAND)wasinventedbyDr.FujioMasuokawhileworkingforToshiba1980.Intelintroducedthefirstco

3、mmercialNORtypeflashchipin1988.NOR-basedflashhaslongeraseandwritetimes,butprovidesfulladdressanddatabuses.ToshibaannouncedNANDflashatthe1987.Ithasreducederaseandwritetimes,andrequireslesschipareaandcell,thusallowinggreaterstoragedesityandlowercostperbitthanNORflash,howevertheI/Oi

4、nterfaceofNANDflashdoesnotprovidearandomaccessexternaladdressbus.FlashmemoryprincipleFlashmemoryprincipleTheinformationisstoredinFlashmemoryasanarrayoffloatinggatetransistors,called“cells”,eachofwhichstoresonebitofinformationtraditionally,Newerflashmemorydevices,referredtoasmulti

5、-levelcelldevices,canstoremorethan1bitpercellbyvaryingthenumberofelectronsplacedonthefloatinggateofacell.Flashmemorycellfunctionsbystoringchargeinthefloatinggate,thepresenceofchargewillthendeterminewhetherthechannelwillconductornot.Duringthereadcyclea“1”attheoutputcorrespondingto

6、thechannelbeinginitslowresistanceorONstate.Thecontrolgateisusedtochargeupthegatecapacitanceduringthewritecycle.Flashmemoryoverview(features)ArrangedintoblocksEachbitinacleanflashchipwillbesettoalogicalone,andcanbesettozerobyawriteoperation.Resettingbitsfromzerotoonecannotbedonein

7、dividually,butonlybyresettingacompleteblock.Memorywear:hasafinitenumberofprogram-erasecycles.(shouldupdateoutofplaceinsteadofinplace)NORvsNANDNORvsNANDOnenandflashDevelopedbySamsungContainraminsidetoemulateNORinterface,whichcombinetheadvantagesofNORandNANDContainbadblockmanagemen

8、tunitinsideRead:sendareadcmdanddirectlyr