OVERVIEWISSI's64MbSynchronousDRAMisorganizedas1,048,576bits x 16-bit x 4-bank for improved performance. Thesynchronous DRAMs achieve high-speed data transferusingpipelinearchitecture.Allinputsandoutputssignalsrefertotherisingedgeoftheclockinput.
1 Meg Bits x 16 Bits x 4 Banks (64-MBIT) SYNCHRONOUS DYNAMIC RAM
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GENERAL DESCRIPTIONThe 64Mb SDRAM is a high speed CMOS, dynamicrandom-access memory designed to operate in 3.3Vmemorysystemscontaining67,108,864bits. Internallyconfigured as a quad-bank DRAM with a synchronousinterface.Each16,777,216-bitbankisorganizedas4,096rowsby256columnsby16bits.
The64MbSDRAMhastheabilitytosynchronouslyburstdataatahighdataratewithautomaticcolumn-addressgeneration,theabilitytointerleavebetweeninternalbanksto hide precharge time and the capability to randomlychange column addresses on each clock cycle duringburstaccess.
SDRAMreadandwriteaccessesareburstorientedstartingataselectedlocationandcontinuingforaprogrammednumber of locations in a programmed sequence. Theregistration of an ACTIVE command begins accesses,followedbyaREADorWRITEcommand.TheACTIVEcommandinconjunctionwithaddressbitsregisteredareusedtoselect thebankandrowtobeaccessed(BA0,BA1selectthebank;A0-A11selecttherow).TheREADor WRITE commands in conjunction with address bitsregisteredareusedtoselectthestartingcolumnlocationfortheburstaccess.
WRITEAburstwriteaccesstoanactiverowisinitiatedwiththeWRITE command. BA0, BA1 inputs selects the bank,and the starting column location is provided by inputsA0-A7.Whether or notAUTO-PRECHARGE is used isdeterminedbyA10.
PRECHARGEThePRECHARGEcommand isused todeactivate theopenrowinaparticularbankortheopenrowinallbanks.BA0,BA1canbeusedtoselectwhichbankisprechargedor they are treated as “Don’t Care”. A10 determineswhetheroneorallbanksareprecharged.Afterexecut-ing this command, the next command for the selectedbank(s)isexecutedafterpassageoftheperiodtRP,whichistheperiodrequiredforbankprecharging.Onceabankhasbeenprecharged,itisintheidlestateandmustbeactivatedpriortoanyREADorWRITEcommandsbeingissuedtothatbank.
AUTO PRECHARGEThe AUTO PRECHARGE function ensures that theprechargeisinitiatedattheearliestvalidstagewithinaburst.Thisfunctionallowsforindividual-bankprechargewithoutrequiringanexplicitcommand.A10canbeusedtoenabletheAUTOPRECHARGEfunction inconjunc-tionwithaspecificREADorWRITEcommand.ForeachindividualREADorWRITEcommand,autoprechargeis
AUTO REFRESH COMMANDThiscommandexecutestheAUTOREFRESHoperation.Therowaddressandbanktoberefreshedareautomaticallygeneratedduringthisoperation. Thestipulatedperiod(trc)isrequiredforasinglerefreshoperation,andnoothercom-mandscanbeexecutedduringthisperiod. Thiscommandisexecutedatleast4096timeseveryTref.DuringanAUTOREFRESHcommand,addressbitsare“Don’tCare”.ThiscommandcorrespondstoCBRAuto-refresh.
SELF REFRESHDuringtheSELFREFRESHoperation,therowaddresstoberefreshed,thebank,andtherefreshintervalaregen-eratedautomaticallyinternally.SELFREFRESHcanbeusedtoretaindataintheSDRAMwithoutexternalclocking,eveniftherestofthesystemispowereddown.TheSELFREFRESHoperationisstartedbydroppingtheCKEpinfromHIGHtoLOW.DuringtheSELFREFRESHoperationallotherinputstotheSDRAMbecome“Don’tCare”.Thedevicemustremaininselfrefreshmodeforaminimumperiodequaltotrasormayremaininselfrefreshmodeforanindefiniteperiodbeyondthat.TheSELF-REFRESHoperationcontinuesaslongastheCKEpinremainsLOWandthereisnoneedforexternalcontrolofanyotherpins.Thenextcommandcannotbeexecuteduntilthedeviceinternal recovery period (trc) has elapsed. Once CKEgoesHIGH,theNOPcommandmustbeissued(minimumof two clocks) to provide time for the completion of anyinternalrefreshinprogress.Aftertheself-refresh,sinceitisimpossibletodeterminetheaddressofthelastrowtoberefreshed,anAUTO-REFRESHshouldimmediatelybeperformedforalladdresses.
BURST TERMINATETheBURSTTERMINATEcommand forcibly terminatestheburstreadandwriteoperationsbytruncatingeitherfixed-length or full-page bursts and the most recentlyregisteredREADorWRITEcommandpriortotheBURSTTERMINATE.
ACTIVE COMMANDWhen the ACTIVE COMMAND is activated, BA0, BA1inputsselectsabanktobeaccessed,andtheaddressinputsonA0-A11selectstherow.UntilaPRECHARGEcommand is issued to thebank, therowremainsopenforaccesses.
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TRUTH TABLE – COMMANDS AND DQM OPERATION(1)
FUNCTION CS RAS CAS WE DQM ADDR DQs
COMMANDINHIBIT(NOP) H X X X X X X
NOOPERATION(NOP) L H H H X X X
ACTIVE(Selectbankandactivaterow)(3) L L H H X Bank/Row X
READ(Selectbank/column,startREADburst)(4) L H L H L/H(8) Bank/Col X
WRITE(Selectbank/column,startWRITEburst)(4) L H L L L/H(8) Bank/Col Valid
BURSTTERMINATE L H H L X X Active
PRECHARGE(Deactivaterowinbankorbanks)(5) L L H L X Code X
AUTOREFRESHorSELFREFRESH(6,7) L L L H X X X(Enterselfrefreshmode)
Power-Down(5) COMMANDINHIBITorNOP ExitPower-Down L H
SelfRefresh(6) COMMANDINHIBITorNOP ExitSelfRefresh L H
ClockSuspend(7) X ExitClockSuspend L H
AllBanksIdle COMMANDINHIBITorNOP Power-DownEntry H L
AllBanksIdle AUTOREFRESH SelfRefreshEntry H L
ReadingorWriting VALID ClockSuspendEntry H L
See TRUTH TABLE – CURRENT STATE BANK n, COMMAND TO BANK n H HNOTES: 1. CKEnisthelogicstateofCKEatclockedgen;CKEn-1 wasthestateofCKEatthepreviousclockedge.2. CurrentstateisthestateoftheSDRAMimmediatelypriortoclockedgen.3. COMMANDnisthecommandregisteredatclockedgen,andACTONnisaresultofCOMMANDn.4. Allstatesandsequencesnotshownareillegalorreserved.5. Exitingpower-downatclockedgenwillputthedeviceintheallbanksidlestateintimeforclockedgen+1 (providedthattcksis
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ABSOLUTE MAXIMUM RATINGS(1)
Symbol Parameters Rating Unit
Vdd max MaximumSupplyVoltage –1.0to+4.6 V Vddqmax MaximumSupplyVoltageforOutputBuffer –1.0to+4.6 V ViN InputVoltage –1.0toVddq +0.5 V Vout OutputVoltage –1.0toVddq +0.5 V Pd max AllowablePowerDissipation 1 W Ics outputShortedCurrent 50 mA Topr operatingTemperature Com. 0to+70 °C Ind. -40to+85 °C A1 -40to+85 °C A2 -40to+105 °C Tstg StorageTemperature –65to+150 °C
DC RECOMMENDED OPERATING CONDITIONS(2) (AtTa=0to+70°Cforcommercialgrade.Ta=-40to+85°CforindustrialandA1grade.Ta=-40to+105°CforA2grade)
Symbol Parameter Min. Typ. Max. Unit
Vdd, Vddq SupplyVoltage 3.0 3.3 3.6 V Vih InputHighVoltage(3) 2.0 — Vdd +0.3 V Vil InputLowVoltage(4) -0.3 — +0.8 V
ReadandwriteaccessestotheSDRAMareburstoriented;accesses start at a selected location and continue fora programmed number of locations in a programmedsequence.AccessesbeginwiththeregistrationofanAC-TIVEcommandwhichisthenfollowedbyaREADorWRITEcommand.TheaddressbitsregisteredcoincidentwiththeACTIVEcommandareusedtoselectthebankandrowtobeaccessed(BA0andBA1selectthebank,A0-A11selecttherow).Theaddressbits(A0-A7)registeredcoincidentwiththeREADorWRITEcommandareusedtoselectthestartingcolumnlocationfortheburstaccess.
Prior to normal operation, the SDRAM must be initial-ized.Thefollowingsectionsprovidedetailedinformationcoveringdeviceinitialization,registerdefinition,commanddescriptionsanddeviceoperation.
InitializationSDRAMs must be powered up and initialized in apredefinedmanner.
WithatleastoneCOMMANDINHIBITorNOPcommandhavingbeenapplied,aPRECHARGEcommandshouldbeappliedoncethe100µsdelayhasbeensatisfied.Allbanksmustbeprecharged.Thiswill leaveallbanksinanidlestate,afterwhichatleasttwoAUTOREFRESHcyclesmustbeperformed. AftertheAUTOREFRESHcyclesarecomplete, the SDRAM is then ready for mode registerprogramming.
The mode register should be loaded prior to applyinganyoperationalcommandbecauseitwillpowerupinanunknownstate.AftertheLoadModeRegistercommand,at least oneNOPcommandmust beassertedprior toanycommand.
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BURST DEFINITION
Burst Starting Column Order of Accesses Within a Burst
Length Address Type = Sequential Type = Interleaved
A0
2 0 0-1 0-1
1 1-0 1-0
A1 A0
0 0 0-1-2-3 0-1-2-3
4 0 1 1-2-3-0 1-0-3-2
1 0 2-3-0-1 2-3-0-1
1 1 3-0-1-2 3-2-1-0
A2 A1 A0
0 0 0 0-1-2-3-4-5-6-7 0-1-2-3-4-5-6-7
0 0 1 1-2-3-4-5-6-7-0 1-0-3-2-5-4-7-6
0 1 0 2-3-4-5-6-7-0-1 2-3-0-1-6-7-4-5
8 0 1 1 3-4-5-6-7-0-1-2 3-2-1-0-7-6-5-4
1 0 0 4-5-6-7-0-1-2-3 4-5-6-7-0-1-2-3
1 0 1 5-6-7-0-1-2-3-4 5-4-7-6-1-0-3-2
1 1 0 6-7-0-1-2-3-4-5 6-7-4-5-2-3-0-1
1 1 1 7-0-1-2-3-4-5-6 7-6-5-4-3-2-1-0
Full n=A0-A7 Cn,Cn+1,Cn+2 NotSupported Page Cn+3,Cn+4... (y) (location0-y) …Cn-1, Cn…
Burst LengthReadandwriteaccessestotheSDRAMareburstoriented,withtheburst lengthbeingprogrammable,asshowninMODEREGISTERDEFINITION.Theburstlengthdeter-minesthemaximumnumberofcolumnlocationsthatcanbeaccessedforagivenREADorWRITEcommand.Burstlengthsof1,2,4or8locationsareavailableforboththesequentialandtheinterleavedbursttypes,andafull-pageburst is available for the sequential type.The full-pageburstisusedinconjunctionwiththeBURSTTERMINATEcommandtogeneratearbitraryburstlengths.
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UNDEFINED
CLK
COMMAND
DQ
READ NOP NOP NOP
CAS Latency - 3
tAC
tOH
DOUT
T0 T1 T2 T3 T4
tLZ
CLK
COMMAND
DQ
READ NOP NOP
CAS Latency - 2
tAC
tOH
DOUT
T0 T1 T2 T3
tLZ
CAS Latency
CAS LatencyTheCAS latency is thedelay, inclockcycles,betweentheregistrationofaREADcommandandtheavailabilityofthefirstpieceofoutputdata.Thelatencycanbesettotwoorthreeclocks.
Afteropeningarow(issuinganACTIVEcommand),aREADorWRITEcommandmaybeissuedtothatrow,subjecttothetrcdspecification.Minimumtrcdshouldbedividedbytheclockperiodandroundeduptothenextwholenumberto determine the earliest clock edge after the ACTIVEcommandonwhichaREADorWRITEcommandcanbeentered.Forexample,atrcdspecificationof20nswitha125MHzclock(8nsperiod)resultsin2.5clocks,roundedto3.Thisisreflectedinthefollowingexample,whichcov-ersanycasewhere2<[trcd(MIN)/tck]≤3.(Thesameprocedureisusedtoconvertotherspecificationlimitsfromtimeunitstoclockcycles).
AsubsequentACTIVEcommandtoadifferentrowinthesamebankcanonlybeissuedafterthepreviousactiverowhasbeen“closed”(precharged).TheminimumtimeintervalbetweensuccessiveACTIVEcommands to thesamebankisdefinedbytrc.
DuringREADbursts,thevaliddata-outelementfromthestarting column address will be available following theCASlatencyaftertheREADcommand.Eachsubsequentdata-outelementwillbevalidbythenextpositiveclockedge.TheCASLatencydiagramshowsgeneral timingforeachpossibleCASlatencysetting.
DatafromanyREADburstmaybetruncatedwithasub-sequent WRITE command, and data from a fixed-lengthREADburstmaybeimmediatelyfollowedbydatafromaWRITEcommand(subjecttobusturnaroundlimitations).TheWRITEburstmaybeinitiatedontheclockedgeim-mediatelyfollowingthelast(orlastdesired)dataelementfromtheREADburst,providedthatI/Ocontentioncanbeavoided.Inagivensystemdesign,theremaybeapos-sibilitythatthedevicedrivingtheinputdatawillgoLow-ZbeforetheSDRAMDQsgoHigh-Z.Inthiscase,atleastasingle-cycledelayshouldoccurbetweenthelastreaddataandtheWRITEcommand.
TheDQMinputisusedtoavoidI/Ocontention,asshowninFiguresRW1andRW2.TheDQMsignalmustbeas-serted (HIGH)at least threeclocksprior to theWRITEcommand(DQMlatencyistwoclocksforoutputbuffers)tosuppressdata-out fromtheREAD.Once theWRITEcommandisregistered,theDQswillgoHigh-Z(orremainHigh-Z),regardlessofthestateoftheDQMsignal,providedtheDQMwasactiveontheclockjustpriortotheWRITEcommandthattruncatedtheREADcommand.Ifnot,thesecondWRITEwillbeaninvalidWRITE.Forexample,ifDQMwasLOWduringT4inFigureRW2,thentheWRITEsatT5andT7wouldbevalid,whiletheWRITEatT6wouldbeinvalid.
In the case of a fixed-length burst being executed tocompletion, a PRECHARGE command issued at theoptimum time (asdescribedabove)provides thesameoperation that would result from the same fixed-lengthburstwithautoprecharge.ThedisadvantageofthePRE-CHARGEcommandisthatitrequiresthatthecommandandaddressbusesbeavailableattheappropriatetimetoissuethecommand;theadvantageofthePRECHARGEcommandisthatitcanbeusedtotruncatefixed-lengthorfull-pagebursts.
Full-pageREADburstscanbetruncatedwiththeBURSTTERMINATE command, and fixed-length READ burstsmaybetruncatedwithaBURSTTERMINATEcommand,providedthatautoprechargewasnotactivated.TheBURSTTERMINATEcommandshouldbeissuedx cyclesbeforetheclockedgeatwhichthelastdesireddataelementisvalid,wherex equalstheCASlatencyminusone.ThisisshownintheREADBurstTerminationdiagramforeachpossibleCASlatency;dataelementn +3isthelastdesireddataelementofalongerburst.
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CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6
READ NOP NOP NOP READ NOP NOP
DOUT n DOUT n+1 DOUT n+2 DOUT n+3 DOUT b
BANK,COL n
BANK,COL b
CAS Latency - 2
x = 1 cycle
DON'T CARE
CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6 T7
READ NOP NOP NOP READ NOP NOP NOP
DOUT n DOUT n+1 DOUT n+2 DOUT n+3 DOUT b
BANK,COL n
BANK,COL b
CAS Latency - 3
x = 2 cycles
Consecutive READ Bursts
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CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5
READ READ READ READ NOP NOP
DOUT n DOUT b DOUT m DOUT x
BANK,COL n
BANK,COL b
CAS Latency - 2
BANK,COL m
BANK,COL x
DON'T CARE
CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6
READ READ READ READ NOP NOP NOP
DOUT n DOUT b DOUT m DOUT x
BANK,COL n
BANK,COL b
CAS Latency - 3
BANK,COL m
BANK,COL x
Random READ Accesses
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CLK
DQM
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5
READ NOP NOP NOP NOP WRITE
BANK,COL n
BANK,COL b
DOUT n DIN b
tDS
tHZ
CAS Latency - 3
RW1 - READ to WRITE
RW2 - READ to WRITE
DON'T CARE
CLK
DQM
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6
READ NOP NOP NOP NOP NOP WRITE
BANK,COL n
DIN b
tDS
tHZ
BANK,COL b
CAS Latency - 2
DOUT n DOUT n+1 DOUT n+2
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CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6 T7
READ NOP NOP NOP NOP NOP ACTIVE
DOUT n DOUT n+1 DOUT n+2 DOUT n+3
BANK a,COL n
BANK a,ROW
BANK(a or all)
CAS Latency - 2
x = 1 cycle
tRP
PRECHARGE
DON'T CARE
CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6 T7
READ NOP NOP NOP NOP NOP ACTIVE
DOUT n DOUT n+1 DOUT n+2 DOUT n+3
BANK,COL n
BANK,COL b
CAS Latency - 3
x = 2 cycles
tRP
BANK a,ROW
PRECHARGE
READ to PRECHARGE
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DON'T CARE
CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6
READ NOP NOP NOP NOP NOP
DOUT n DOUT n+1 DOUT n+2 DOUT n+3
BANK a,COL n
CAS Latency - 2
x = 1 cycle
BURSTTERMINATE
DON'T CARE
CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6 T7
READ NOP NOP NOP NOP NOP NOP
DOUT n DOUT n+1 DOUT n+2 DOUT n+3
BANK,COL n
CAS Latency - 3
x = 2 cycles
BURSTTERMINATE
READ Burst Termination
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Data for a fixed-length WRITE burst may be followedby,or truncatedwith,aPRECHARGEcommandto thesamebank(providedthatautoprechargewasnotacti-vated), anda full-pageWRITEburstmaybe truncatedwithaPRECHARGEcommand to thesamebank.ThePRECHARGEcommandshouldbeissuedtwraftertheclockedgeatwhichthelastdesiredinputdataelementisregistered.Theautoprechargemoderequiresatwrofatleastoneclockplustime,regardlessoffrequency.Inaddition,whentruncatingaWRITEburst,theDQMsignalmustbeusedtomaskinputdatafortheclockedgepriorto,andtheclockedgecoincidentwith,thePRECHARGEcommand.AnexampleisshownintheWRITEtoPRE-CHARGEdiagram.Datan+1iseitherthelastofaburstoftwoorthelastdesiredofalongerburst.FollowingthePRECHARGEcommand,asubsequentcommandtothesamebankcannotbeissueduntiltrpismet.
Fixed-lengthorfull-pageWRITEburstscanbetruncatedwiththeBURSTTERMINATEcommand.Whentruncat-ingaWRITEburst,theinputdataappliedcoincidentwiththeBURSTTERMINATEcommandwillbeignored.Thelastdatawritten(providedthatDQMisLOWatthattime)willbe the inputdataappliedoneclockpreviousto theBURSTTERMINATEcommand.ThisisshowninWRITEBurstTermination,wheredatan isthelastdesireddataelementofalongerburst.
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CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3
WRITE NOP NOP NOP
DIN n DIN n+1
BANK,COL n
DON'T CARE
CLK
COMMAND
ADDRESS
DQ
T0 T1 T2
WRITE NOP WRITE
DIN n DIN n+1 DIN b
BANK,COL n
BANK,COL b
DON'T CARE
WRITE Burst
WRITE to WRITE
CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3
WRITE WRITE WRITE WRITE
DIN n DIN b DIN m DIN x
BANK,COL n
BANK,COL b
BANK,COL m
BANK,COL x
Random WRITE Cycles
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CLK
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5
WRITE NOP READ NOP NOP NOP
DIN n DIN n+1 DOUT b DOUT b+1
BANK,COL n
BANK,COL b
CAS Latency - 2
WRITE to READ
WP1 - WRITE to PRECHARGE
DON'T CARE
CLK
DQM
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6
WRITE NOP NOP ACTIVE NOP NOP
BANK a,COL n
BANK a,ROW
BANK(a or all)
tWR
tRP
PRECHARGE
DIN n DIN n+1
CAS Latency - 2
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CLK
COMMAND
ADDRESS
DQ
T0 T1 T2
WRITE
DIN n (DATA)
BANK,COL n
DON'T CARE
(ADDRESS)
BURSTTERMINATE
NEXTCOMMAND
WRITE Burst Termination
DON'T CARE
CLK
DQM
COMMAND
ADDRESS
DQ
T0 T1 T2 T3 T4 T5 T6
WRITE NOP NOP NOP ACTIVE NOP
BANK a,COL n
BANK a,ROW
BANK(a or all)
tWR
tRP
PRECHARGE
DIN n DIN n+1
CAS Latency - 3
WP2 - WRITE to PRECHARGE
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CLK
CKEHIGH
ALL BANKS
BANK SELECT
BANK ADDRESS
CS
RAS
CAS
WE
A0-A9, A11
A10
BA0, BA1
DON'T CARE
CLK
CKE
COMMAND NOP NOP ACTIVE
≥ tCKStCKS
All banks idle
Enter power-down mode Exit power-down mode
tRCD
tRAS
tRC
Input buffers gated off
PRECHARGE Command
POWER-DOWN
POWER-DOWNPower-downoccursifCKEisregisteredLOWcoincidentwithaNOPorCOMMANDINHIBITwhennoaccessesareinprogress.Ifpower-downoccurswhenallbanksareidle,thismodeisreferredtoasprechargepower-down;ifpower-downoccurswhenthereisarowactiveineitherbank, this mode is referred to as active power-down.Entering power-down deactivates the input and outputbuffers,excludingCKE,formaximumpowersavingswhileinstandby.Thedevicemaynotremaininthepower-downstatelongerthantherefreshperiod(64ms)sincenorefreshoperationsareperformedinthismode.
CONCURRENT AUTO PRECHARGEAnaccesscommand(READorWRITE)toanotherbankwhileanaccesscommandwithautoprechargeenabledisexecutingisnotallowedbySDRAMs,unlesstheSDRAMsupports CONCURRENT AUTO PRECHARGE. ISSI
