数字逻辑设计及应用教学课件：10-1 memory.ppt

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1、Chapter10MemoryWhatisthememorylike?Memoryweusuallyreservetheword“memory”torefertobitsthataresortedinastructuredway,usuallyasatwo-dimensionalarrayinwhichonerowofbitsisaccessedatatime.(P799)Readonlymemory(ROM)只读存储器ROMisnonvolatilememory(非易失性存储器)；thatis,itscontentsarepreservedevenifnopowerisapplied.

2、Memory-not!(P800)1AA...0n1decoderA...icellb1...1D......Wi0cellDn...1Bitline...2-1DataOutputDW...001cellcellWMemorycellsWordlineW2n-1AddressinputsMemoryWordline:eachdecoderoutputiscalleda“wordline”becauseitselectsoneroworwordofthetablestoredintheROM.Bitline:Thebitlinecorrespondstooneoutputbitofthe

3、ROM.Readonlymemory(ROM)MaskROM:useadiodeortransistorasmemoryconnection.Thedatacanonlybewriteinthemanufactureprocess,cannotbechangedbytheusers!Active-highdecoderoutput(wordline)Readonlymemory(ROM)P-ROM:Programmable,addafusetothediode.Thefusecanbemeltedbytheusertowrite“0”!A0A0W0=1,ACTIVEHIGHW0W1W2W

4、3D3D2D1D0A1A1010通通001通0或门阵列输出表达式与门阵列输出表达式ROM存储内容的真值表0101101001111110D3D2D1D0存储内容00011011A1A0地址MemoryConstructwithabinarydecoderandamemoryarray!MemoryDatabitsarestoredinastructuredwayOnceawordlineisselected,allthebitsinthislinecanbeinoutputthroughthebitlines!MemoryExample:Whena2a1a0=000,y4y3y2y1=1

5、000;Whena2a1a0=101,y4y3y2y1=0110;MemoryAmemorycanbetreatedasacombinationalcircuit!Atruthtableisstoredinthememoryarray!Eachbitlineisafunctionoutput!MemoryExample:Readonlymemory(ROM)AND-ORstructure:EachwordlineisanoutputofANDgate;EachbitlineisanoutputofORgate.9.1.4CommercialROMTypesMaskROMPROMEPROM

6、(OTP)ROMEEPROMFlashEPROMReadonlymemory(ROM)EPROM(可擦除可编程只读存储器):ErasablePROM,usefloating-gatetechnology.IncludeEEPROMandFLASH.Thefloatinggatecanbechargedtowrite“0”andunchargedtowrite“1”!Randomaccessmemory(RAM)Usememorydevicetostoredatabit,andusewordlinetocontrolitsinput/outputfrombitline.StaticRAM(

7、SRAM)Thememorydeviceisalatch,thedataisstable,andtheaccesstimeisshort,butthecircuitiscomplexandexpensive!DynamicRAM(DRAM)ThememorydeviceiscapacitorVerysimple,highdensity;Theoutputsignalisveryweak,asenseamplifierisneeded