数字电子技术(Floyd 第十版)课件Chapter -10-st.ppt
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数字电子技术(Floyd 第十版)课件Chapter -10-st.ppt
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,DigitalFundamentalsTenthEditionFloyd,Chapter10,Memoriesstoredatainunitsfromonetoeightbits.Themostcommonunitisthebyte,whichbydefinitionis8bits.,Summary,MemoryUnits,Computermemoriesareorganizedintomultiplesofbytescalledwords.Generally,awordisdefinedasthenumberofbitshandledasoneentitybyacomputer.Bythisdefinition,awordisequaltotheinternalregistersize(usually16,32,or64bits).,Forhistoricalreasons,assemblylanguagedefinesawordasexactlytwobytes.Inassemblylanguage,a32bitentityiscalledadouble-wordand64bitsisdefinedasaquad-word.,Thelocationofaunitofdatainamemoryiscalledtheaddress.InPCs,abyteisthesmallestunitofdatathatcanbeaccessed.,Summary,MemoryUnits,Ina2-dimensionalarray,abyteisaccessedbysupplyingarownumber.Forexamplethebluebyteislocatedinrow7.,A3-dimensionalarrayisarrangedasrowsandcolumns.Eachbytehasauniquerowandcolumnaddress.,Summary,MemoryAddressing,Question,Howmanybytesareshown?
Whatisthelocationofthebluebyte?
Answers,b)Row2,column8,Thisexampleis(ofcourse)onlyforillustration.Typicalcomputermemorieshave256MBormoreofcapacity.,a)64B,Inordertoreadorwritetoaspecificmemorylocation,abinarycodeisplacedontheaddressbus.Internaldecodersdecodetheaddresstodeterminethespecificlocation.Dataisthenmovedtoorfromthedatabus.,Summary,MemoryAddressing,Theaddressbusisagroupofconductorswithacommonfunction.Itssizedeterminesthenumberoflocationsthatcanbeaccessed.A32bitaddressbuscanaccess232locations,whichisapproximately4G.,Summary,MemoryAddressing,Inadditiontotheaddressbusanddatabus,semiconductormemorieshavereadandwritecontrolsignalsandchipselectsignals.Dependingonthetypeofmemory,othersignalsmayberequired.,Summary,ReadandWriteOperations,Thetwomainmemoryoperationsarecalledreadandwrite.Asimplifiedwriteoperationisshowninwhichnewdataoverwritestheoriginaldata.Datamovestothememory.,Theaddressisplacedontheaddressbus.Dataisplacedonthedatabus.Awritecommandisissued.,Addressregister,Dataregister,Addressbus,Addressdecoder,Byteorganizedmemoryarray,Write,Databus,Summary,ReadandWriteOperations,Thereadoperationisactuallya“copy”operation,astheoriginaldataisnotchanged.Thedatabusisa“two-way”path;datamovesfromthememoryduringareadoperation.,Theaddressisplacedontheaddressbus.Areadcommandisissued.Acopyofthedataisplacedinthedatabusandshiftedintothedataregister.,Addressregister,Dataregister,Addressbus,Addressdecoder,Byteorganizedmemoryarray,Read,Databus,RAMisfortemporarydatastorage.Itisread/writememoryandcanstoredataonlywhenpowerisapplied,henceitisvolatile.TwocategoriesarestaticRAM(SRAM)anddynamicRAM(DRAM).,Summary,RandomAccessMemory,Bitsstoredinasemiconductorlatchorflip-flop,Bitsstoredaschargeonacapacitor,SRAMusessemiconductorlatchmemorycells.Thecellsareorganizedintoanarrayofrowsandcolumns.,Summary,StaticRAM,SRAMisfasterthanDRAMbutismorecomplex,takesupmorespace,andismoreexpensive.SRAMsareavailableinmanyconfigurationsatypicallargeSRAMisorganizedas512kX8bits.,Summary,AsynchronousStaticRAM,ThebasicorganizationofanasynchronousSRAMisshown.,Readcyclesequence:
AvalidaddressisputontheaddressbusChipselectisLOWOutputenableisLOWDataisplacedonthedatabus,Writecyclesequence:
AvalidaddressisputontheaddressbusChipselectisLOWWriteenableisLOWDataisplacedonthedatabus,Addresslines,Addresslines,Eightinputbuffers,I/O0,I/O7,Outputdata,Rowdecoder,Memoryarray,ColumnI/O,Columndecoder,256rowsx128columnsx8bits,Inputdatacontrol,SeetextFigure10-12forthewaveforms,Summary,DynamicRAM(DRAM),DynamicRAMs(DRAMs)storedatabitsasachargeonacapacitor.,DRAMsaresimpleandcosteffective,butrequirerefreshcircuitrytopreventlosingdata.Theaddresslinesaremultiplexedtoreducethenumberofaddresslines.,RowaddressislatchedwhenRASisLOW,ColumnaddressislatchedwhenCASisLOW,Addresses,RAS,CAS,Multiplexedaddresslines:
Summary,DynamicRAM(DRAM),AfeaturewithsomeDRAMsisfastpagemode.Fastpagemodeallowssuccessivereadorwriteoperationsfromaseriesofcolumnsaddressthatareallonthesamerow.,Addresses,RAS,CAS,R/W,DOUT,OthertypesofDRAMshavebeendevelopedtospeedaccessandmaketheprocessormoreefficient.TheseincludeEDODRAMs,BEDODRAMsandSDRAMs,asdescribedinthetext.,Summary,Read-OnlyMemory(ROM),TheROMfamilyisallconsiderednon-volatile,becauseitretainsdatawithpowerremoved.Itincludesvariousmembersthatcanbeeitherpermanentmemoryorerasable.,ROMsareusedtostoredatathatisnever(orrarely)changedsuchassysteminitializationfiles.ROMsarenon-volatile,meaningtheyretainthedatawhenpowerisremoved,althoughsomeROMscanbereprogrammedusingspecializedequipment.,Summary,Read-OnlyMemory(ROM),AROMsymbolisshownwithtypicalinputsandoutputs.Thetrianglesontheoutputsindicateitisatri-stateddevice.,ToreadavaluefromtheROM,anaddressisplacedontheaddressbus,thechipisenabled,andashorttimelater(calledtheaccesstime),dataappearsonthedatabus.,Addressinputlines,A0,A1,A2,A3,A4,A5,A6,A7,O0,O1,O2,O3,Dataoutputlines,Addressinputlines,Dataoutputs,Addresstransition,Dataoutputtransition,ta,Chipselect,Validdataonoutputlines,Validaddressoninputlines,Summary,PROMs,EPROMsandEEPROMs,PROMsareprogrammableROM,inwhichafusedlinkisburnedopenduringtheprogrammingprocess.OncethePROMisprogrammed,itcannotbereversed.,AnEPROMisanerasablePROMandcanbeerasedbyexposuretoUVlightthroughawindow.Toprogramit,ahighvoltageisappliedtoVPPandOEisbroughtLOW.,O0,O1,O2,O3,O4,O5,O6,O7,A0,A1,A2,A3,A4,A5,A6,A7,A8,A9,A10,CE/PGM,OE,VPP,AnothertypeoferasablePROMistheEEPROM,whichcanbeerasedandprogrammedwithelectricalpulses.,Summary,FlashMemory,Flashmemoriesarehighdensityread/writememoriesthatarenonvolatile.Theyhavetheabilitytoretainchargeforyearswithnoappliedpower.,FlashmemoryusesaMOStransistorwithafloatinggateasthebasicstoragecell.Thefloatinggatecanstorecharge(logic0)whenapositivevoltageisappliedtothecontrolgate.Withlittleornocharge,thecellstoresalogic1.,logic0isstored,logic1isstored,Theflashmemorycellcanbereadbyapplyingapositivevoltagetothecontrolgate.Ifthecellisstoringa1,thepositivevoltageissufficienttoturnonthetransistor;ifitisstoringa0,thetransistorisoff.,Summary,FlashMemory,Flashmemoriesarrangedinarrayswithanactiveload.Forsimplicity,onlyonecolumnisshown.Whenaspecificrowandcolumnisselectedduringareadoperation,theactiveloadhascurrent.,Onedrawbacktoflashmemoryisthatonceabithasbeensetto0,itcanberesettoa1onlybyerasinganentireblockofmemory.Anotherlimitationisthatflashmemoryhasalargebutfinitenumberofread/writecycles.,Summary,MemoryExpansion,Memorycanbeexpandedineitherwordsizeorwordcapacityorboth.,Toexpandwordsize:
Noticethatthedatabussizeislarger,butthenumberofaddressisthesame.,Summary,MemoryExpansion,Toexpandwordcapacity,youneedtoaddanaddresslineasshowninthisexample,Noticethatthedatabussizedoesnotchange.,Question,Whatisthepurposeoftheinverter?
Answer,OnlyoneoftheICsisenabledatanytimedependingonthelogicontheaddedaddressline.,Summary,SIMMsandDIMMs,SIMMs(singlein-linememorymodules)andDIMMs(dualin-linememorymodules)areplug-incircuitboardscontainingtheICsandI/Obroughtoutonedgeconnectors.SIMMshavea32-bitdatapathwithI/OononlyonesidewhereasDIMMshavea64-bitdatapathwithI/Oonbothsidesoftheboard.,SIMMorDIMM,Socketonsystemboard,Summary,FIFOMemory,FIFOmeansfirstin-firstout.Thistypeofmemoryisbasicallyanarrangementofshiftregisters.Itisusedinapplicationswheretwosystemscommunicateatdifferentrates.,Summary,LIFOMemory,LIFOmeanslastin-firstout.Inmicroprocessors,aportionofRAMisdevotedtothistypeofmemory,whichiscalledthestack.Stacksareveryusefulfortemporarystorageofinternalregisters,sothattheprocessorcanbeinterruptedbutcaneasilyreturntoagiventask.,Aspecialregister,calledthestackpointer,keepstrackofthelocationthatdatawaslaststoredonthestack.Thiswillbethenextdatatobetakenfromthestackwhenneeded.,Top-of-stack,Stackpointer,Summary,MagneticHardDrive,Themagneticharddriveisthebackboneofcomputermassstorageandisappliedtootherdevicessuchasdigitalvideorecorders.Capacitiesofharddriveshaveincreasedexponentially,with1TB(1trillionbytes!
)drivesavailabletoday.,Plattersarearrangedintracks(circularshapes)andsectors(pieshaped).FilesarelistedinaFileAllocationTable,(FAT)thatkeepstrackoffilenames,locations,size,andmore.,Harddrivewithcoverremoved,Summary,OpticalStorage,Thecompactdisk(CD)usesalasertoburntinypitsintothemedia.Surroundingthepitsareflatareascalledlands.TheCDcanbereadusingalow-powerIRlaserthatdetectsthedifferencebetweenpitsandlands.,Binarydataisencodedwithaspecialmethodcallednegativenon-returntozeroencoding.Achangefromapittoalandoralandtoapitrepresentsabinaryone,whereasnochangerepresentsazero.Astandard120mmCDcanholdapproximately700MBofdata.,SelectedKeyTerms,AddressCapacitySRAMDRAMPROM,Thelocationofagivenstoragecellorgroupofcellsinmemory.,Thetotalnumberofdataunits(bits,nibbles,bytes,words)thatamemorycanstore.,Staticrandomaccessmemory;atypeofvolatileread/writesemiconductormemory.,D
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