microprocessors 1 basics

8/4/2019 Microprocessors 1 Basics

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Microprocessor1

Dr.SufyanSamara

ComputerEngineeringDepartment

AnNajahNa>onalUniversity

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Objec>vesandnotes Provideanunderstandingofmicroprocessors,

theirstructure,andtheassemblylanguage.

Threeexamsandsomehomeworks. Textbook:

TheintelmicroprocessorsbyBarryB.Brey

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History

500B.C.Babyloniansinventedtheabacus In1642mathema>cianBlaisePascalinventedacalculatorconstructedof

gearsandwheels.

Firstprac>calgearedmechanicalmachinestocomputeinforma>ondatetoearly1800s

handheldelectroniccalculator. firstappearedinearly1970s

In1889,HermanHollerithdevelopedthepunchedcardforstoringdata. GermaninventorKonradZuse,inventedthefirstmodern

electromechanicalcomputer.

HisZ3calcula>ngcomputerprobablyinventedforaircra\andmissiledesign.

duringWorldWarIIfortheGermanwareffort Z3arelaylogicmachineclockedat5.33Hz.

farslowerthanlatestmul>pleGHzmicroprocessors

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Historycont. ElectronicNumericalIntegratorandCalculator(ENIAC),ahugemachine. over17,000vacuumtubes;500milesofwires weighedover30tons about100,000opera>onspersecond

Programmedbyrewiringitscircuits. processtookmanyworkersseveraldays workerschangedelectricalconnec>onsonplug-boardslikeearly

telephoneswitchboards

Requiredfrequentmaintenance. vacuumtubeservicelifeaproblem

FirstmicroprocessordevelopedatIntelCorpora>onin1971 Thefirst,machinelanguage,wasconstructedofonesandzeros

usingbinarycodes. storedinthecomputermemorysystemasgroupsofinstruc>ons

calledaprogram

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Historycont. Mathema>cianJohnvonNeumannfirstmodernpersontodevelopa

systemtoacceptinstruc>onsandstoretheminmemory.

Computersareo\encalledvonNeumannmachinesinhishonor. Assemblerallowsprogrammertousemnemoniccodes

suchasADDforaddi>on Inplaceofabinarynumber.

suchas01000111 Assemblylanguageanaidtoprogramming. 1957GraceHopperdevelopedfirsthigh-levelprogramminglanguage

calledFLOWMATIC. computersbecameeasiertoprogram

Insameyear,IBMdevelopedFORTRANFORmulaTRANslator)foritssystems. Allowedprogrammerstodevelopprogramsthatusedformulastosolve

mathema>calproblems. FORTRANiss>llusedbysomescien>stsforcomputerprogramming.

Similarlanguage,ALGOL(ALGOrithmicLanguage)introducedaboutayearlater

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Historycont. Firstsuccessful,widespreadprogramminglanguagefor

businessapplica>onswasCOBOL(COmputerBusinessOrientedLanguage).

SomecommonmodernprogramminglanguagesareBASIC,C#,C/C++,Java,PASCAL,andADA.

Assemblylanguages>llplaysimportantrole. manyvideogameswrienalmostexclusively

inassemblylanguage

AssemblyalsointerspersedwithC/C++toperformmachinecontrolfunc>onsefficiently. somenewerparallelinstruc>onsfoundonPen>umandCore2

microprocessorsonlyprogrammableinassemblylanguage

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TheMicroprocessorAge WorldsfirstmicroprocessortheIntel4004.

A4-bitmicroprocessor-programmablecontrolleronachip. Addressed4096,4-bit-widememoryloca>ons.

abitisabinarydigitwithavalueofoneorzero 4-bit-widememoryloca>ono\encalledanibble

The4004instruc>onsetcontained45instruc>ons. Fabricatedwiththen-currentstate-of-the-artP-channelMOSFET

technology.

Executedinstruc>onsat50KIPs(kilo-instruconspersecond). slowcomparedto100,000instruc>onspersecondby30-tonENIACcomputer

in1946

Differencewasthat4004weighedlessthananounce. 4-bitmicroprocessordebutedinearlygamesystemsandsmallcontrol

systems. earlyshuffleboardgameproducedbyBailey

Mainproblemswithearlymicroprocessorwerespeed,wordwidth,andmemorysize. TexasInstrumentsandothersalsoproduced4-bitmicroprocessors.

s>llsurvivesinlow-endapplica>onssuchasmicrowaveovensandsmallcontrolsystems

Calculatorss>llbasedon4-bitBCD(binary-codeddecimal)codes7

TheMicroprocessorAgecont. Intelreleased8008in1971.

extended8-bitversionof4004microprocessor Addressedexpandedmemoryof16Kbytes.

Abyteisgenerallyan8-bit-widebinarynumberandaKis1024.

memorysizeo\enspecifiedinKbytes Containedaddi>onalinstruc>ons,48total. Providedopportunityforapplica>oninmore

advancedsystems.

engineersdevelopeddemandingusesfor80088


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TheMicroprocessorAgecont. Intelintroduced8080microprocessorin1973. firstofthemodem8-bitmicroprocessors MotorolaCorpora>onintroducedMC6800microprocessorabout

sixmonthslater.

8080and,toalesserdegree,theMC6800wereabreakthroughintheageofthemicroprocessor. othercompaniessoonintroducedtheirownversionsofthe8-bit

microprocessor

8080addressedfour>mesmorememory. 64Kbytesvsl6Kbytesfor8008

Executedaddi>onalinstruc>ons;10xfaster. addi>ontaking20sonan8008-basedsystemrequiredonly2.0son

an8080-basedsystem

TTL(transistor-transistorlogic)compa>ble. the8008wasnotdirectlycompa>ble

Interfacingmadeeasierandlessexpensive.9

The8085Microprocessor In1977IntelCorpora>onintroducedan

updatedversionofthe8080the8085.

Last8-bit,general-purposemicroprocessordevelopedbyIntel.

Slightlymoreadvancedthan8080;executedso\wareatanevenhigherspeed.

769,230instruc>onspersecondvs500,000persecondonthe8080).

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TheModernMicroprocessor

In1978Intelreleasedthe8086;ayearorsolater,itreleasedthe8088.

Bothdevicesare16-bitmicroprocessors. executedinstruc>onsinaslileas400ns(2.5millionsofinstruconspersecond)

majorimprovementoverexecu>onspeedof8085 8086&8088addressed1Mbyteofmemory.

16>mesmorememorythanthe8085

1M-bytememorycontains1024Kbyte-sizedmemoryloca>onsor1,048,576bytes

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TheModernMicroprocessorcont. Higherspeedandlargermemorysizeallowed8086&8088

toreplacesmallerminicomputersinmanyapplica>ons.

Anotherfeaturewasa4-or6-byteinstruc>oncacheorqueuethatprefetchedinstruc>onsbeforetheywereexecuted. queuespedopera>onofmanysequencesofinstruc>on basisforthemuchlargerinstruc>oncaches

foundinmodemmicroprocessors.

ThesemicroprocessorsarecalledCISC(complexinstruconsetcomputers). addi>onalinstruc>onseasedtaskofdevelopingefficientand

sophis>catedapplica>ons

16-bitmicroprocessoralsoprovidedmoreinternalregisterstoragespace. addi>onalregistersallowedso\waretobe

wrienmoreefficiently

evolvedtomeetneedforlargermemorysystems12


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TheModernMicroprocessorcont.

PopularityofIntelensuredin1981whenIBMchosethe8088initspersonalcomputer.

Spreadsheets,wordprocessors,spellingcheckers,andcomputer-basedthesauruses

werememory-intensive.

requiredmorethan64Kbytesofmemoryfoundin8-bitmicroprocessorstoexecuteefficiently

The16-bit8086and8088provided1Mbyteofmemoryfortheseapplica>ons

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The80286Microprocessor Eventhe1M-bytememorysystemprovedlimi>ngfordatabasesandotherapplica>ons. Intelintroducedthe80286in1983 anupdated8086

Almostiden>caltothe8086/8088. addressed16M-bytememorysysteminstead

ofa1M-bytesystem

Instruc>onsetalmostiden>calexceptforafewaddi>onalinstruc>ons. managedtheextra15Mbytesofmemory

80286clockspeedincreasedin8.0Mhzversion. executedsomeinstruc>onsinaslileas250ns(4.0MIPs)

Somechangestointernalexecu>onofinstruc>onsledtoeigholdincreaseinspeedformanyinstruc>ons

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The32-BitMicroprocessor Applica>onsdemandedfastermicroprocessorspeeds,more

memory,andwiderdatapaths. Ledtothe80386in1986byIntel.

majoroverhaulof16-bit808680286architecture Intelsfirstprac>calmicroprocessortocontaina32-bitdatabus

and32-bitmemoryaddress. Intelproducedanearlier,unsuccessful32-bitmicroprocessorcalled

iapx-432

Through32-bitbuses,80386addressedupto4Gbytesofmemory. 1Gmemory=1024M,or1,073,741,824loca>ons 1,000,000typewrien,double-spacedpagesofASCIItextdata

80386SXaddressed16Mbytesofmemorythrougha16-bitdataand24-bitaddressbus.

80386SL/80386SLCaddressed32Mbytesmemoryvia16-bitdata,25-bitaddressbus.

80386SLCcontainedaninternalcachetoprocessdataatevenhigherrates.

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The32-BitMicroprocessorcont. 32-bitmicroprocessorneededduetosizeofitsdatabus.

transfersreal(single-precisionfloa>ng-point)numbersthatrequire32-bit-widememory

Toprocess32-bitrealnumbers,themicroprocessormustefficientlypassthembetweenitselfandmemory. with8-bitdatabus,takesfourreadorwritecycles onlyonereadorwritecycleisrequiredfor32bit

Significantlyincreasesspeedofanyprogramthatmanipulatesrealnumbers.

High-levellanguages,spreadsheets,anddatabasemanagementsystemsuserealnumbersfordatastorage. alsousedingraphicaldesignpackagesthatusevectorstoplotimages

onthevideoscreen

CAD(computer-aideddraing/design)systemsasAUTOCAD,ORCAD 80386hadhigherclockingspeedsandincludedamemory

managementunit. allowedmemoryresourcestobeallocated

andmanagedbytheopera>ngsystem16


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The80486Microprocessor

In1989Intelreleasedthe8048. Highlyintegratedpackage. 80386-likemicroprocessor. 80387-likenumericcoprocessor. 8K-bytecachememorysystem. Internalstructureof80486modifiedsoabouthalfof

itsinstruc>onsexecutedinoneclockinsteadoftwoclocks. ina50MHzversion,abouthalfofinstruc>onsexecutedin

25ns(50MIPs)

50%over80386operatedatsameclockspeed Double-clocked80486DX2executedinstruc>onsat66

MHz,withmemorytransfersat33MHz. calledadouble-clockedmicroprocessor

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ThePenumMicroprocessor Introduced1993,Pen>umwassimilarto80386and80486microprocessors. OriginallylabeledtheP5or80586.

Inteldecidednottouseanumberbecauseitappearedtobeimpossibletocopyrightanumber

Introductoryversionsoperatedwithaclockingfrequencyof60MHz&66MHz,andaspeedof110MIPs.

Double-clockedPen>umat120MHzand133MHz,alsoavailable. fastestversionproduced233MHzPen>um

athreeandone-halfclockedversion

Cachesizewasincreasedto16Kbytesfromthe8Kcachefoundin80486.

8K-byteinstruc>oncacheanddatacache. Memorysystemupto4Gbytes. Databuswidthincreasedtoafull64bits. Databustransferspeed60MHzor66MHz.

dependingontheversionofthePen>um18


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TheInteliCOMP-ra>ngindex

Tocomparespeedsofmicroprocessors,InteldevisedtheiCOMP-ra>ngindex.

compositeofSPEC92,ZDBench,PowerMeter TheiCOMP1ra>ngindexisusedtoratethe

speedofallIntelmicroprocessorsthroughthePen>um.

Figure12showsrela>vespeedsofthe80386DX25MHzversionthroughthePen>um233MHzversion.

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TheInteliCOMP2-ra>ngindex.

A\erPen>umII Switchedto

iCOMP2-ra>ng

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TheMemoryandI/OSystem MemorystructureofallIntel-basedpersonalcomputerssimilar

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Mainmemorysystemdividedintothreeparts: TPA(transientprogramarea) systemarea XMS(extendedmemorysystem)

First1Mbyteofmemoryo\encalledtherealorconven>onalmemorysystem. Intelmicroprocessorsdesignedtofunc>on

inthisareausingrealmodeopera>on

80286throughtheCore2containtheTPA(640Kbytes)andsystemarea(384Kbytes). alsocontainextendedmemory o\encalledATclassmachines

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TheTPA Thetransientprogramarea(TPA)holdstheDOS

(diskoperangsystem)opera>ngsystem;other

programsthatcontrolthecomputersystem.

InterruptvectorsaccessDOS,BIOS(basicI/Osystem),andapplica>ons.

AreascontaintransientdatatoaccessI/Odevicesandinternalfeaturesofthesystem. thesearestoredintheTPAsotheycanbechangedas

DOSoperates

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TheSystemArea

Thesystemareacontainsprogramsonread-only(ROM)orflashmemory,andareasof

read/write(RAM)memoryfordatastorage.

containsROM/RAMdatafromdevicessuchasthevideodisplayRAM,thevideocontrol

programsonROMorflashmemory,andthe

SystemBIOSROM.

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I/OSpace I/Odevicesallowthemicroprocessorto

communicatewiththeoutsideworld.

I/O(input/output)spaceinacomputersystemextendsfromI/Oport0000HtoportFFFFH

I/Oportaddressissimilartoamemoryaddressinsteadofmemory,itaddressesanI/Odevice

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TheMicroprocessor CalledtheCPU(centralprocessingunit)

ControlsmemoryandI/Othroughconnec>onscalledbuses. Microprocessorperformsthreemaintasks:

datatransferbetweenitselfandthememoryorI/Osystems simplearithme>candlogicopera>ons programflowviasimpledecisions

Buses Acommongroupofwiresthatinterconnectcomponentsina

computersystem.

Transferaddress,data,&controlinforma>onbetweenmicroprocessor,memoryandI/O.

Threebusesexistforthistransferofinforma>on:address,data,andcontrol.

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Theblockdiagramofacomputer

system

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Buses

Theaddressbusrequestsamemoryloca>onfromthememoryoranI/Oloca>onfromthe

I/Odevices.

Thedatabustransfersinforma>onbetweenthemicroprocessoranditsmemoryandI/O

addressspace

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Buses ControlbuslinesselectandcausememoryorI/O

toperformareadorwriteopera>on.

Inmostcomputersystems,therearefourcontrolbusconnec>ons:

MRDC(memoryreadcontrol) MWTC (memorywritecontrol) IORC (I/Oreadcontrol) IOWC (I/Owritecontrol). overbarindicatesthecontrolsignalisac>ve-low;

(ac>vewhenlogiczeroappearsoncontrolline)

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opera>on

Themicroprocessorreadsamemoryloca>onbysendingthememoryanaddressthroughtheaddressbus.

Next,itsendsamemoryreadcontrolsignaltocausethememorytoreaddata.

Datareadfrommemoryarepassedtothemicroprocessorthroughthedatabus.

Wheneveramemorywrite,I/Owrite,orI/Oreadoccurs,thesamesequenceiscarriedout.

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NUMBERSYSTEMS Useofamicroprocessorrequiresworking

knowledgeofnumberingsystems.

binary,decimal,andhexadecimal Conversionsaredescribed.

decimalandbinarydecimalandhexadecimalbinaryandhexadecimal

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TheNumbersystem

Decimal0-9 Hexadecimal0F Octal0-7 Binary0,1

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ConversiontoDecimal Toconvertfromanynumberbasetodecimal,

determinetheweightsorvaluesofeachposi>on

ofthenumber.

Sumtheweightstoformthedecimalequivalent.

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ConversionfromDecimal Conversionsfromdecimaltoothernumber

systemsmoredifficulttoaccomplish.

Toconvertthewholenumberpor>onofanumbertodecimal,divideby1radix.

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WholeNumberConversionfromDecimal

Toconvertadecimalwholenumbertoanothernumbersystem,dividebytheradixandsave

remaindersassignificantdigitsoftheresult.

Analgorithmforthisconversion:dividethedecimalnumberbytheradix

(numberbase)

savetheremainder(firstremainderistheleastsignificantdigit)

repeatsteps1and2un>lthequo>entiszero36


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Toconvert10decimaltobinary,divideitby2.

theresultis5,witharemainderof0 Firstremainderisunitsposi>onoftheresult.

inthisexample,a0 Next,dividethe5by2;resultis2,witha

remainderof1.

the1isthevalueofthetwos(2 1)posi>on Con>nuedivisionun>lthequo>entisazero.

Theresultiswrienas10102fromtheboomtothetop.

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ConverngfromaDecimalFracon Conversionisaccomplishedwithmul>plica>onby

theradix.

Wholenumberpor>onofresultissavedasasignificantdigitoftheresult.

frac>onalremainderagainmul>pliedbytheradixwhenthefrac>onremainderiszero,mul>plica>on

ends

Somenumbersarenever-ending(repetend).azeroisneveraremainder

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Algorithmforconversionfromadecimalfrac>on:

mul>plythedecimalfrac>onbytheradix(numberbase).

savethewholenumberpor>onoftheresult(evenifzero)asadigit;firstresultiswrien

immediatelytotherightoftheradixpoint

repeatsteps1and2,usingthefrac>onalpartofstep2un>lthefrac>onalpartofstep2iszero

Sametechniqueconvertsadecimalfrac>onintoanynumberbase.

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Binary-CodedHexadecimal Binary-codedhexadecimal(BCH)isahexadecimal

numberwrieneachdigitisrepresentedbya4-

bitbinarynumber.

BCHcodeallowsabinaryversionofahexadecimalnumbertobewrieninaformeasilyconverted

betweenBCHandhexadecimal.

Hexadecimalrepresentedbyconver>ngdigitstoBCHcodewithaspacebetweeneachdigit.

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Complements At>mes,dataarestoredincomplementformto

representnega>venumbers.

Twosystemsusedtorepresentnega>vedata:radixradix-1complement(earliest)

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14COMPUTERDATAFORMATS Successfulprogrammingrequiresaprecise

understandingofdataformats.

Commonly,dataappearasASCII,Unicode,BCD,signedandunsignedintegers,andfloa>ng-point

numbers(realnumbers).

Otherformsareavailablebutarenotcommonlyfound.

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ASCIIandUnicodeData ASCII(AmericanStandardCodeforInformaonInterchange)datarepresentalphanumeric

charactersincomputermemory.

StandardASCIIcodeisa7-bitcode.eighthandmostsignificantbitusedtoholdparity

Ifusedwithaprinter,mostsignificantbitsare0foralphanumericprin>ng;1forgraphics.

InPC,anextendedASCIIcharactersetisselectedbyplacing1inthele\mostbit.

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ManyWindows-basedapplica>onsusetheUnicodesystemtostorealphanumericdata.storeseachcharacteras16-bitdata

Codes0000H00FFHarethesameasstandardASCIIcode.

Remainingcodes,0100HFFFFH,storeallspecialcharactersfrommanycharactersets.

Allowsso\wareforWindowstobeusedinmanycountriesaroundtheworld.

Forcompleteinforma>ononUnicode,visit:h+p://www.unicode.org

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BCD(Binary-CodedDecimal)Data TherangeofaBCDdigitextendsfrom00002to

10012,or09decimal,storedintwoforms:

Storedinpackedform:packedBCDdatastoredastwodigitsperbyte;usedforBCDaddi>onandsubtrac>oninthe

instruc>onsetofthemicroprocessor

Storedinunpackedform:unpackedBCDdatastoredasonedigitperbytereturnedfromakeypadorkeyboard

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Byte-SizedData Storedasunsignedandsignedintegers. Differenceintheseformsistheweightofthe

le\mostbitposi>on.

value128fortheunsignedintegerminus128forthesignedinteger

Insignedintegerformat,thele\mostbitrepresentsthesignbitofthenumber.

alsoaweightofminus128

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Figure114Theunsignedandsignedbytesillustra>ngtheweightsofeachbinary-bitposi>on.

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Unsignedintegersrange00HtoFFH(0255) Signedintegersfrom-128to0to+127. Nega>vesignednumbersrepresentedinthisway

arestoredinthetwoscomplementform.

Evalua>ngasignednumberbyusingweightsofeachbitposi>onismucheasierthantheactof

twoscomplemen>nganumbertofinditsvalue.

especiallytrueintheworldofcalculatorsdesignedforprogrammers

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Word-SizedData Aword(16-bits)isformedwithtwobytesofdata. Theleastsignificantbytealwaysstoredinthe

lowest-numberedmemoryloca>on.

Mostsignificantbyteisstoredinthehighest. Thismethodofstoringanumberiscalledthelileendianformat.

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Alternatemethodiscalledthebigendianformat. Numbersarestoredwiththelowestloca>oncontainingthemostsignificantdata. NotusedwithIntelmicroprocessors. ThebigendianformatisusedwiththeMotorola

familyofmicroprocessors.

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Doubleword-sizeddatarequiresfourbytesofmemorybecauseitisa32-bitnumber.

appearsasaproducta\eramul>plica>onalsoasadividendbeforeadivision

Defineusingtheassemblerdirec>vedefinedoubleword(s),orDD.

alsousetheDWORDdirec>veinplaceofDD

Doubleword-SizedData

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RealNumbers Sincemanyhigh-levellanguagesuseIntelmicroprocessors,realnumbersareo\en

encountered.

Areal,orafloang-pointnumbercontainstwoparts:

aman>ssa,significand,orfrac>onanexponent.

A4-bytenumberiscalledsingle-precision. The8-byteformiscalleddouble-precision.

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Theassemblercanbeusedtodefinerealnumbersinsingle-&double-precisionforms:usetheDDdirec>veforsingle-precision32-bit

numbers

usedefinequadword(s),orDQtodefine64-bitdouble-precisionrealnumbers

Op>onaldirec>vesareREAL4,REAL8,andREAL10.

fordefiningsingle-,double-,andextendedprecisionrealnumbers

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21INTERNALMICROPROCESSOR

ARCHITECTURE

Beforeaprogramiswrienorinstruc>oninves>gated,internalconfigura>onofthe

microprocessormustbeknown.

8086throughCore2consideredprogramvisible. registersareusedduringprogrammingandarespecifiedby

theinstruc>ons

Otherregistersconsideredtobeprograminvisible. notaddressabledirectlyduringapplica>onsprogramming

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MulpurposeRegisters RAX-a64-bitregister(RAX),a32-bitregister(accumulator)(EAX),a16-bitregister(AX),oraseitheroftwo8-bitregisters(AHandAL).

Theaccumulatorisusedforinstruc>onssuchasmul>plica>on,division,andsomeoftheadjustmentinstruc>ons.

Intelplanstoexpandtheaddressbusto52bitstoaddress4P(peta)bytesofmemory.

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RBX,addressableasRBX,EBX,BX,BH,BL.

BXregister(baseindex)some>mesholdsoffsetaddressofaloca>oninthememorysysteminall

versionsofthemicroprocessor

RCX,asRCX,ECX,CX,CH,orCL.a(count)general-purposeregisterthatalsoholdsthe

countforvariousinstruc>ons

RDX,asRDX,EDX,DX,DH,orDL.a(data)general-purposeregisterholdsapartoftheresultfromamul>plica>onorpartofdividendbeforeadivision

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RBP,asRBP,EBP,orBP.pointstoamemory(basepointer)loca>on

formemorydatatransfers RDIaddressableasRDI,EDI,orDI.

o\enaddresses(desnaonindex)stringdes>na>ondataforthestringinstruc>ons

RSIusedasRSI,ESI,orSI.the(sourceindex)registeraddressessourcestring

dataforthestringinstruc>ons

likeRDI,RSIalsofunc>onsasageneral-purposeregister

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R8-R15foundinthePen>um4andCore2if64-bitextensionsareenabled.dataareaddressedas64-,32-,16-,or8-bit

sizesandareofgeneralpurpose

Mostapplica>onswillnotusetheseregistersun>l64-bitprocessorsarecommon.

the8-bitpor>onistherightmost8-bitonlybits8to15arenotdirectlyaddressableas

abyte

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Special-PurposeRegisters IncludeRIP,RSP,andRFLAGS

segmentregistersincludeCS,DS,ES,SS,FS,andGS RIPaddressesthenextinstruc>oninasec>onof

memory.

definedas(instruconpointer)acodesegment RSPaddressesanareaofmemorycalled

thestack.

the(stackpointer)storesdatathroughthispointer

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RFLAGSindicatethecondi>onofthemicroprocessorandcontrolitsopera>on.

Figure22showstheflagregistersofallversionsofthemicroprocessor.

Flagsareupward-compa>blefromthe8086/8088throughCore2.

Therightmostfiveandtheoverflowflagarechangedbymostarithme>candlogicopera>ons.

althoughdatatransfersdonotaffectthem

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Figure22TheEFLAGandFLAGregistercountsfortheen>re8086andPen>um

microprocessorfamily.

Flagsneverchangeforanydatatransferorprogramcontrolopera>on.

Someoftheflagsarealsousedtocontrolfeaturesfoundinthemicroprocessor.

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Flagbits,withabriefdescrip>onoffunc>on. C(carry)holdsthecarrya\eraddi>onorborrowa\ersubtrac>on.

alsoindicateserrorcondi>ons P(parity)isthecountofonesinanumber

expressedasevenorodd.Logic0foroddparity;

logic1forevenparity.

ifanumbercontainsthreebinaryonebits,ithasoddparity

ifanumbercontainsnoonebits,ithasevenparity

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ListofEachFlagbit,withabrief

descrip>onoffunc>on.

C(carry)holdsthecarrya\eraddi>onorborrowa\ersubtrac>on.

alsoindicateserrorcondi>ons P(parity)isthecountofonesinanumber

expressedasevenorodd.Logic0foroddparity;

logic1forevenparity.

ifanumbercontainsthreebinaryonebits,ithasoddparity;Ifanumbercontainsnoonebits,it

hasevenparity

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A(auxiliarycarry)holdsthecarry(half-carry)a\eraddi>onortheborrowa\ersubtrac>onbetweenbitposi>ons3and4oftheresult.

Z(zero) showsthattheresultofanarithme>corlogicopera>oniszero.

S(sign)flagholdsthearithme>csignoftheresulta\eranarithme>corlogicinstruc>onexecutes.

T(trap) Thetrapflagenablestrappingthroughanon-chipdebuggingfeature.

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I(interrupt)controlsopera>onoftheINTR(interruptrequest)inputpin.

D(direcon) selectsincrementordecrementmodefortheDIand/orSIregisters.

O(overflow) occurswhensignednumbersareaddedorsubtracted.

anoverflowindicatestheresulthasexceededthecapacityofthemachine

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IOPLusedinprotectedmodeopera>ontoselecttheprivilegelevelforI/Odevices.

NT(nestedtask)flagindicatesthecurrenttaskisnestedwithinanothertaskinprotectedmode

opera>on.

RF(resume) usedwithdebuggingtocontrolresump>onofexecu>ona\erthenext

instruc>on.

VM(virtualmode)flagbitselectsvirtualmodeopera>oninaprotectedmodesystem.

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AC,(alignmentcheck)flagbitac>vatesifawordordoublewordisaddressedonanon-wordornon-doublewordboundary.

VIFisacopyoftheinterruptflagbitavailabletothePen>um4(virtualinterrupt)

VIP(virtual)providesinforma>onaboutavirtualmodeinterruptfor(interruptpending)Pen>um.

usedinmul>taskingenvironmentstoprovidevirtualinterruptflags

70


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ID(idenficaon) flagindicatesthatthePen>ummicroprocessorssupporttheCPUIDinstruc>on.

CPUIDinstruc>onprovidesthesystemwithinforma>onaboutthePen>ummicroprocessor

71

SegmentRegisters Generatememoryaddresseswhencombinedwith

otherregistersinthemicroprocessor.

Fourorsixsegmentregistersinvariousversionsofthemicroprocessor.

Asegmentregisterfunc>onsdifferentlyinrealmodethaninprotectedmode.

Followingisalistofeachsegmentregister,alongwithitsfunc>oninthesystem.

72


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CS(code)segmentholdscode(programsandprocedures)usedbythemicroprocessor.

DS(data)containsmostdatausedbyaprogram.Dataareaccessedbyanoffsetaddressorcontentsof

otherregistersthatholdtheoffsetaddress

ES(extra)anaddi>onaldatasegmentusedbysomeinstruc>onstoholddes>na>ondata.

73

22REALMODEMEMORYADDRESSING

80286andaboveoperateineithertherealorprotectedmode.

Realmodeoperaonallowsaddressingofonlythefirst1MbyteofmemoryspaceeveninPen>um4

orCore2microprocessor.

thefirst1Mbyteofmemoryiscalledthe realmemory,convenonalmemory ,orDOSmemorysystem


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SegmentsandOffsets Allrealmodememoryaddressesmustconsistofa

segmentaddressplusanoffsetaddress.

segmentaddressdefinesthebeginningaddressofany64K-bytememorysegment

offsetaddressselectsanyloca>onwithinthe64Kbytememorysegment

Figure23showshowthesegmentplusoffsetaddressingschemeselectsamemoryloca>on.

Figure23Therealmodememory-addressingscheme,usingasegmentaddressplusan

offset.

thisshowsamemorysegmentbeginningat

10000H,endingat

loca>on1FFFFH 64Kbytesinlength

alsoshowshowanoffsetaddress,calleda

displacement,ofF000H

selectsloca>on

1F000Hinthememory


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Oncethebeginningaddressisknown,theendingaddressisfoundbyaddingFFFFH.becausearealmodesegmentofmemoryis64Kin

length

Theoffsetaddressisalwaysaddedtothesegmentstar>ngaddresstolocatethedata.

Segmentandoffsetaddressissome>meswrienas1000:2000.

asegmentaddressof1000H;anoffsetof2000H

DefaultSegmentandOffsetRegisters

Themicroprocessorhasrulesthatapplytosegmentswhenevermemoryisaddressed.

thesedefinethesegmentandoffsetregistercombina>on

Thecodesegmentregisterdefinesthestartofthecodesegment.

Theinstruconpointerlocatesthenextinstruc>onwithinthecodesegment.


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Anotherofthedefaultcombina>onsisthestack.

stackdataarereferencedthroughthestacksegmentatthememoryloca>onaddressedbyeitherthestack

pointer(SP/ESP)orthepointer(BP/EBP)

Figure24showsasystemthatcontainsfourmemorysegments.

amemorysegmentcantouchoroverlapif64Kbytesofmemoryarenotrequiredforasegment

Figure24Amemorysystemshowingtheplacementoffourmemorysegments.

thinkofsegmentsaswindowsthatcanbe

movedoveranyarea

ofmemorytoaccessdata

orcode

aprogramcanhavemorethanfourorsixsegments,

butonlyaccessfourorsixsegmentsata>me


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Figure25Anapplica>onprogramcontainingacode,data,andstacksegmentloadedintoaDOSsystemmemory.

aprogramplacedinmemorybyDOSisloadedintheTPAatthefirstavailableareaof

memoryabovedriversand

otherTPAprograms

areaisindicatedbyafree-pointermaintainedbyDOS

programloadingishandledautoma>callybytheprogram

loaderwithinDOS

SegmentandOffsetAddressingScheme

AllowsRelocaon

SegmentplusoffsetaddressingallowsDOSprogramstoberelocatedinmemory.

Arelocatableprogramisonethatcanbeplacedintoanyareaofmemoryandexecutedwithout

change.

Relocatabledataaredatathatcanbeplacedinanyareaofmemoryandusedwithoutanychangetotheprogram.


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Becausememoryisaddressedwithinasegmentbyanoffsetaddress,thememorysegmentcanbemovedtoanyplaceinthememorysystem

withoutchanginganyoftheoffsetaddresses.

Onlythecontentsofthesegmentregistermustbechangedtoaddresstheprogram

inthenewareaofmemory.

Windowsprogramsarewrienassumingthatthefirst2Gofmemoryareavailableforcodeand

data.

24MEMORYPAGING

Thememorypagingmechanismallowsanyphysicalmemoryloca>ontobeassignedtoanylinearaddress.

Iinearaddressisdefinedastheaddressgeneratedbyaprogram.

Physicaladdressistheactualmemoryloca>onaccessedbyaprogram.

Withmemorypaging,thelinearaddressisinvisiblytranslatedtoanyphysicaladdress.


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PagingRegisters Thepagingunitiscontrolledbythecontents

ofthemicroprocessorscontrolregisters.

BeginningwithPen>um,anaddi>onalcontrolregisterlabeledCR4controlsextensionstothe

basicarchitecture.

SeeFigure211forthecontentsofcontrolregistersCR0throughCR4.

Figure211Thecontrolregisterstructureofthemicroprocessor.


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Thelinearaddress,asgeneratedbyso\ware,isbrokenintothreesec>onsthatareusedtoaccessthepagedirectoryentry,pagetableentry,and

memorypageoffsetaddress.

Figure212showsthelinearaddressanditsmakeupforpaging.

Whentheprogramaccessesaloca>onbetween00000000Hand00000FFFH,themicroprocessor

physicallyaddressesloca>on00100000H

00100FFFH.

Figure212Theformatforthelinearaddress(a)andapagedirectoryorpagetableentry(b).#


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IntelhasincorporatedaspecialtypeofcachecalledTLB(translaonlook-asidebuffer).

becauserepaginga4K-bytesec>onofmemoryrequiresaccesstothepagedirectoryandapagetable,bothlocatedinmemory

The80486cacheholdsthe32mostrecentpagetransla>onaddresses.

ifthesameareaofmemoryisaccessed,theaddressisalreadypresentintheTLB

Thisspeedsprogramexecu>on Pen>umcontainsseparateTLBsforeachoftheirinstruc>onanddatacaches.

ThePageDirectoryandPageTable Onlyonepagedirectoryinthesystem. Thepagedirectorycontains1024doubleword

addressesthatlocateupto1024pagetables.

Pagedirectoryandeachpagetableare4Kbytesinlength.

Figure213showsthepagedirectory,afewpagetables,andsomememorypages.


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Figure213Thepagingmechanisminthe80386throughCore2microprocessors.#

25FlatModeMemory Aflatmodememorysystemisoneinwhichthere

isnosegmenta>on.

doesnotuseasegmentregistertoaddressaloca>oninthememory

Firstbyteaddressisat0000000000H;thelastloca>onisatFFFFFFFFFFH.

addressis40-bits Thesegmentregisters>llselectstheprivilegelevel

oftheso\ware.


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Figure215The64-bitflatmodememorymodel.

31DATAADDRESSINGMODES

MOVinstruc>onisacommonandflexibleinstruc>on. providesabasisforexplana>onofdata-addressingmodes

Figure31illustratestheMOVinstruc>onanddefinesthedirec>onofdataflow.

Sourceistotherightanddesnaonthele\,nexttotheopcodeMOV.

anopcode,oropera>oncode,tellsthemicroprocessorwhichopera>ontoperform


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Figure31TheMOVinstruc>onshowingthesource,des>na>on,anddirec>onofdataflow.

Figure32showsallpossiblevaria>onsofthedata-addressingmodesusingMOV.

Thesedata-addressingmodesarefoundwithallversionsoftheIntelmicroprocessor.

exceptforthescaled-index-addressingmode,foundonlyin80386throughCore2

RIPrela>veaddressingmodeisnotillustrated.onlyavailableonthePen>um4andCore2

inthe64-bitmode


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Figure328086Core2data-addressingmodes.

RegisterAddressing Themostcommonformofdataaddressing.

onceregisternameslearned,easiesttoapply. Themicroprocessorcontainsthese8-bitregister

namesusedwithregisteraddressing:AH,AL,BH,

BL,CH,CL,DH,andDL.

16-bitregisternames:AX,BX,CX,DX,SP,BP,SI,andDI.


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In80386&above,extended32-bitregisternamesare:EAX,EBX,ECX,EDX,ESP,EBP,EDI,andESI.

64-bitmoderegisternamesare:RAX,RBX,RCX,RDX,RSP,RBP,RDI,RSI,andR8throughR15.

Importantforinstruc>onstouseregistersthatarethesamesize.

nevermixan8-bitwitha16-bitregister,an8-ora16-bitregisterwitha32-bitregister

thisisnotallowedbythemicroprocessorandresultsinanerrorwhenassembled

Figure33Theeffectofexecu>ngtheMOVBX,CXinstruc>onatthepointjustbeforetheBXregisterchanges.Notethatonlytherightmost16bitsofregisterEBXchange.


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Figure33showstheopera>onoftheMOVBX,CXinstruc>on.

Thesourceregisterscontentsdonotchange.thedes>na>onregisterscontentsdochange

Thecontentsofthedes>na>onregisterordes>na>onmemoryloca>onchangeforall

instruc>onsexcepttheCMPandTEST

instruc>ons.

TheMOVBX,CXinstruc>ondoesnotaffectthele\most16bitsofregisterEBX.

ImmediateAddressing Termimmediateimpliesthatdataimmediately

followthehexadecimalopcodeinthememory.

immediatedataareconstantdatadatatransferredfromaregisterormemoryloca>on

arevariabledata

Immediateaddressingoperatesuponabyteorwordofdata.

Figure34showstheopera>onofaMOVEAX,13456Hinstruc>on.


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Figure34Theopera>onoftheMOVEAX,3456Hinstruc>on.Thisinstruc>oncopiestheimmediatedata(13456H)intoEAX.

AswiththeMOVinstruc>onillustratedinFigure33,thesourcedataoverwritesthedes>na>ondata.

Insymbolicassemblylanguage,thesymbol#precedesimmediatedatainsomeassemblers.MOVAX,#3456Hinstruc>onisanexample

Mostassemblersdonotusethe#symbol,butrepresentimmediatedataasintheMOVAX,

3456Hinstruc>on.

anolderassemblerusedwithsomeHewle-Packardlogicdevelopmentdoes,asmayothers

inthistext,the#isnotusedforimmediatedata


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Thesymbolicassemblerportraysimmediatedatainmanyways.

TheleerHappendshexadecimaldata. Ifhexadecimaldatabeginwithaleer,the

assemblerrequiresthedatastartwitha0.

torepresentahexadecimalF2,0F2Hisusedinassemblylanguage

Decimaldataarerepresentedasisandrequirenospecialcodesoradjustments.

anexampleisthe100decimalintheMOVAL,100instruc>on

AnASCII-codedcharacterorcharactersmaybedepictedintheimmediateformiftheASCIIdataareenclosedinapostrophes.

becarefultousetheapostrophe()forASCIIdata

BinarydataarerepresentedifthebinarynumberisfollowedbytheleerB.

insomeassemblers,theleerY


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Eachstatementinanassemblylanguageprogramconsistsoffourpartsorfields.

Thele\mostfieldiscalledthelabel.usedtostoreasymbolicnameforthememory

loca>onitrepresents

Alllabelsmustbeginwithaleeroroneofthefollowingspecialcharacters:@,$,-,or?.

alabelmayanylengthfrom1to35characters Thelabelappearsinaprogramtoiden>fythe

nameofamemoryloca>onforstoringdataandforotherpurposes.

Thenextfieldtotherightistheopcodefield.designedtoholdtheinstruc>on,oropcodetheMOVpartofthemovedatainstruc>onisan

exampleofanopcode

Rightoftheopcodefieldistheoperandfield.containsinforma>onusedbytheopcodetheMOVAL,BLinstruc>onhastheopcodeMOVand

operandsALandBL

Thecommentfield,thefinalfield,containsacommentabouttheinstruc>on(s).

commentsalwaysbeginwithasemicolon(;)


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DirectDataAddressing Appliedtomanyinstruc>onsinatypicalprogram. Twobasicformsofdirectdataaddressing:

directaddressing,whichappliestoaMOVbetweenamemoryloca>onandAL,AX,orEAX

displacementaddressing,whichappliestoalmostanyinstruc>onintheinstruc>onset

Addressisformedbyaddingthedisplacementtothedefaultdatasegmentaddressoranalternate

segmentaddress.

DirectAddressing DirectaddressingwithaMOVinstruc>ontransfers

databetweenamemoryloca>on,locatedwithin

thedatasegment,andtheAL(8-bit),AX(16-bit),

orEAX(32-bit)register.

usuallya3-bytelonginstruc>on MOVAL,DATAloadsALfromthedatasegment

memoryloca>onDATA(1234H).

DATAisasymbolicmemoryloca>on,while1234Histheactualhexadecimalloca>on


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Figure35Theopera>onoftheMOVAL,[1234H]instruc>onwhenDS=1000H.

Thisinstruc>ontransfersacopycontentsofmemoryloca>on11234HintoAL.

theeffec>veaddressisformedbyadding1234H(theoffsetaddress)and10000H(thedatasegmentaddressof1000H>mes

10H)inasystemopera>ngintherealmode

DisplacementAddressing Almostiden>caltodirectaddressing,exceptthe

instruc>onis4byteswideinsteadof3.

In80386throughPen>um4,thisinstruc>oncanbeupto7byteswideifa32-bitregisteranda32-

bitdisplacementarespecified.

Thistypeofdirectdataaddressingismuchmoreflexiblebecausemostinstruc>onsuseit.


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RegisterIndirectAddressing Allowsdatatobeaddressedatanymemory

loca>onthroughanoffsetaddressheldinanyof

thefollowingregisters:BP,BX,DI,andSI.

Inaddi>on,80386andaboveallowregisterindirectaddressingwithanyextendedregister

exceptESP.

Inthe64-bitmode,thesegmentregistersservenopurposeinaddressingaloca>on

intheflatmodel.

Figure36Theopera>onoftheMOVAX,[BX]instruc>onwhenBX=1000HandDS=0100H.Notethatthisinstruc>onisshowna\erthecontentsofmemoryaretransferredtoAX.#


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ThedatasegmentisusedbydefaultwithregisterindirectaddressingoranyothermodethatusesBX,DI,orSItoaddressmemory.

IftheBPregisteraddressesmemory,thestacksegmentisusedbydefault.

thesesengsareconsideredthedefaultforthesefourindexandbaseregisters

Forthe80386andabove,EBPaddressesmemoryinthestacksegmentbydefault.

EAX,EBX,ECX,EDX,EDI,andESIaddressmemoryinthedatasegmentbyfault.

Whenusinga32-bitregistertoaddressmemoryintherealmode,contentsoftheregistermustneverexceed0000FFFFH.

Inthe64-bitmode,segmentregistersarenotusedinaddresscalcula>on;theregister

containstheactuallinearmemoryaddress.


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Insomecases,indirectaddressingrequiresspecifyingthesizeofthedatabythespecialassemblerdirecveBYTEPTR,WORDPTR,

DWORDPTR,orQWORDPTR.

thesedirec>vesindicatethesizeofthememorydataaddressedbythememorypointer(PTR)

Thedirec>vesarewithinstruc>onsthataddressamemoryloca>onthrougha

pointerorindexregisterwithimmediatedata.

WithSIMDinstruc>ons,theoctalOWORDPTR,representsa128-bit-widenumber.

Indirectaddressingo\enallowsaprogramtorefertotabulardatalocatedinmemory.

Figure37showsthetableandtheBXregisterusedtosequen>allyaddresseachloca>oninthe

table.

Toaccomplishthistask,loadthestar>ngloca>onofthetableintotheBXregister

withaMOVimmediateinstruc>on.

A\erini>alizingthestar>ngaddressofthetable,useregisterindirectaddressingto

storethe50samplessequen>ally.


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Figure37Anarray(TABLE)containing50bytesthatareindirectlyaddressedthroughregisterBX.

Base-Plus-IndexAddressing Similartoindirectaddressingbecauseitindirectly

addressesmemorydata.

Thebaseregistero\enholdsthebeginningloca>onofamemoryarray.

theindexregisterholdstherela>veposi>onofanelementinthearray

wheneverBPaddressesmemorydata,boththestacksegmentregisterandBPgeneratetheeffec>ve

address


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LocangDatawithBase-Plus-Index

Addressing

Figure38showshowdataareaddressedbytheMOVDX,[BX+DI]instruc>onwhenthe

microprocessoroperatesintherealmode.

TheIntelassemblerrequiresthisaddressingmodeappearas[BX][DI]insteadof[BX+DI].

TheMOVDX,[BX+DI]instruc>onisMOVDX,[BX][DI]foraprogramwrienfortheIntelASMassembler.

Figure38Anexampleshowinghowthebase-plus-indexaddressingmodefunc>onsfortheMOVDX,[BX

+DI]instruc>on.No>cethatmemoryaddress02010HisaccessedbecauseDS=0100H,BX=100Hand

DI=0010H.

#


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LocangArrayDataUsingBase-Plus-Index

Addressing

Amajoruseistoaddresselementsinamemoryarray.

Toaccomplishthis,loadtheBXregister(base)withthebeginningaddressofthearrayandtheDI

register(index)withtheelementnumbertobe

accessed.

Anexampleofthebase-plus-indexaddressingmode.Hereanelement(DI)ofanARRAY(BX)isaddressed.


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RegisterRelaveAddressing Similartobase-plus-indexaddressingand

displacementaddressing.

datainasegmentofmemoryareaddressedbyaddingthedisplacementtothecontentsofabaseoranindex

register(BP,BX,DI,orSI)

Figure310showstheopera>onoftheMOVAX,[BX+1000H]instruc>on.

Arealmodesegmentis64Kbyteslong.

Figure310Theopera>onoftheMOVAX,[BX+1000H]instructon,whenBX=1000HandDS=0200H.#


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AddressingArrayDatawithRegisterRelave

Itispossibletoaddressarraydatawithregisterrela>veaddressing.

suchaswithbase-plus-indexaddressing InFigure311,registerrela>veaddressingis

illustratedwiththesameexampleasforbase-

plus-indexaddressing.

thisshowshowthedisplacementARRAYaddstoindexregisterDItogenerateareferencetoanarrayelement

Figure311Registerrela>veaddressingusedtoaddressanelementofARRAY.ThedisplacementaddressesthestartofARRAY,andDIaccessesanelement.


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BaseRelave-Plus-IndexAddressing

Similartobase-plus-indexaddressing.addsadisplacementusesabaseregisterandanindexregisterto

formthememoryaddress

Thistypeofaddressingmodeo\enaddressesatwo-dimensionalarrayofmemorydata.

AddressingDatawithBaseRelave-Plus-

Index

Least-usedaddressingmode. Figure312showshowdataarereferencedifthe

instruc>onexecutedbythemicroprocessoris

MOVAX,[BX+SI+100H].

displacementof100HaddstoBXandSItoformtheoffsetaddresswithinthedatasegment

Thisaddressingmodeistoocomplexforfrequentuseinprogramming.


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Figure312Anexampleofbaserela>ve-plus-indexaddressingusingaMOVAX,[BX+SI+1000H]instruc>on.Note:DS=1000H#

AddressingArrayswithBaseRelave-Plus-

Index

Supposeafileofmanyrecordsexistsinmemory,eachrecordwithmanyelements.

displacementaddressesthefile,baseregisteraddressesarecord,theindexregisteraddressesan

elementofarecord

Figure313illustratesthisverycomplexformofaddressing.


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Figure313Baserela>ve-plus-indexaddressingusedtoaccessaFILEthatcontainsmul>plerecords(REC).

DataStructures Usedtospecifyhowinforma>onisstoredina

memoryarray.

atemplatefordata Thestartofastructureisiden>fiedwiththe

STRUCassemblylanguagedirec>veandtheend

withtheENDSstatement.


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32PROGRAMMEMORY-ADDRESSING

MODES

UsedwiththeJMP(jump)andCALLinstruc>ons. Consistofthreedis>nctforms:

direct,rela>ve,andindirect

DirectProgramMemoryAddressing Usedforalljumpsandcallsbyearly

microprocessor;alsousedinhigh-levellanguages,

suchasBASIC.

GOTOandGOSUBinstruc>ons Themicroprocessorusesthisform,butnotas

o\enasrela>veandindirectprogrammemory

addressing.

Theinstruc>onsfordirectprogrammemoryaddressingstoretheaddresswiththeopcode.


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Figure314The5-bytemachinelanguageversionofaJMP[10000H]instruc>on.

ThisJMPinstruc>onloadsCSwith1000HandIPwith0000Htojumptomemoryloca>on10000Hforthenextinstruc>on.

anintersegmentjumpisajumptoanymemoryloca>onwithintheen>rememorysystem

O\encalledafarjumpbecauseitcanjumptoanymemoryloca>onforthenextinstruc>on.

inrealmode,anyloca>onwithinthefirst1MbyteInprotectedmodeopera>on,thefarjumpcanjump

toanyloca>oninthe4G-byteaddressrangeinthe80386-Core2microprocessors


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Theonlyotherinstruc>onusingdirectprogramaddressingistheintersegmentorfarCALLinstruc>on.

Usually,thenameofamemoryaddress,calledalabel,referstotheloca>onthatiscalledor

jumpedtoinsteadoftheactualnumericaddress.

WhenusingalabelwiththeCALLorJMPinstruc>on,mostassemblersselectthebestform

ofprogramaddressing.

RelaveProgramMemoryAddressing

Notavailableinallearlymicroprocessors,butitisavailabletothisfamilyofmicroprocessors.

ThetermrelaGvemeansrela>vetotheinstruc>onpointer(IP).

TheJMPinstruc>onisa1-byteinstruc>on,witha1-byteora2-bytedisplacementthataddstothe

instruc>onpointer.

AnexampleisshowninFigure315.


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Figure315AJMP[2]instruc>on.Thisinstruc>onskipsoverthe2bytesofmemorythatfollowtheJMPinstruc>on.

IndirectProgramMemoryAddressing

ThemicroprocessorallowsseveralformsofprogramindirectmemoryaddressingfortheJMP

andCALLinstruc>ons.

In80386andabove,anextendedregistercanbeusedtoholdtheaddressorindirectaddressofa

rela>veJMPorCALL.

forexample,theJMPEAXjumpstotheloca>onaddressbyregisterEAX


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Ifarela>veregisterholdstheaddress,thejumpisconsideredtobeanindirectjump.

Forexample,JMP[BX]referstothememoryloca>onwithinthedatasegmentattheoffset

addresscontainedinBX.

atthisoffsetaddressisa16-bitnumberusedastheoffsetaddressintheintrasegmentjump

thistypeofjumpissome>mescalledan indirect-indirectordouble-indirectjump

Figure316showsajumptablethatisstored,beginningatmemoryloca>onTABLE.

Figure316Ajumptablethatstoresaddressesofvariousprograms.TheexactaddresschosenfromtheTABLEisdeterminedbyanindexstoredwiththejumpinstruc>on.


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33STACKMEMORY-ADDRESSINGMODES

Thestackplaysanimportantroleinallmicroprocessors.

holdsdatatemporarilyandstoresreturnaddressesusedbyprocedures

StackmemoryisLIFO(last-in,first-out)memorydescribesthewaydataarestoredandremovedfrom

thestack

DataareplacedonthestackwithaPUSHinstrucon;removedwithaPOPinstrucon.

Stackmemoryismaintainedbytworegisters:thestackpointer(SPorESP)thestacksegmentregister(SS)

Wheneverawordofdataispushedontothestack,thehigh-order8bitsareplacedintheloca>on

addressedbySP1.

low-order8bitsareplacedintheloca>onaddressedbySP2


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TheSPisdecrementedby2sothenextwordisstoredinthenextavailablestackloca>on.

theSP/ESPregisteralwayspointstoanareaofmemorylocatedwithinthestacksegment.

Inprotectedmodeopera>on,theSSregisterholdsaselectorthataccessesadescriptorforthebaseaddressofthestacksegment.

Whendataarepoppedfromthestack,thelow-order8bitsareremovedfromtheloca>onaddressedbySP.

high-order8bitsareremoved;theSPregisterisincrementedby2

Figure317ThePUSHandPOPinstruc>ons:(a)PUSHBXplacesthecontentsofBXontothestack;(b)

POPCXremovesdatafromthestackandplacesthemintoCX.Bothinstruc>onsareshowna\er

execu>on.


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NotethatPUSHandPOPstoreorretrievewordsofdataneverbytesin8086-80286.

80386andaboveallowwordsordoublewordstobetransferredtoandfromthestack.

Datamaybepushedontothestackfromany16-bitregisterorsegmentregister.

in80386andabove,fromany32-bitextendedregister Datamaybepoppedoffthestackintoany

registeroranysegmentregisterexceptCS.

PUSHAandPOPAinstruc>onspushorpopallexceptsegmentregisters,onthestack.

Notavailableonearly8086/8088processors. 80386andaboveallowextendedregisterstobe

pushedorpopped.

64-bitmodeforPen>umandCore2doesnotcontainaPUSHAorPOPAinstruc>on


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Introducon Thischapterconcentratesonthedatamovement

instruc>ons.

Thedatamovementinstruc>onsincludeMOV,MOVSX,MOVZX,PUSH,POP,BSWAP,XCHG,XLAT,

IN,OUT,LEA,LDS,LES,LFS,LGS,LSS,LAHF,SAHF.

Stringinstruc>ons:MOVS,LODS,STOS,INS,andOUTS.

ChapterObjecves

Explaintheopera>onofeachdatamovementinstruc>onwithapplicableaddressingmodes.

Explainthepurposesoftheassemblylanguagepseudo-opera>onsandkeywordssuchasALIGN,

ASSUME,DB,DD,DW,END,ENDS,ENDP,

EQU,.MODEL,OFFSET,ORG,PROC,PTR,

SEGMENT,USEI6,USE32,andUSES.

Uponcompleonofthischapter,youwillbeableto:


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ChapterObjecves

Selecttheappropriateassemblylanguageinstruc>ontoaccomplishaspecificdata

movementtask.

Determinethesymbolicopcode,source,des>na>on,andaddressingmodefora

hexadecimalmachinelanguageinstruc>on.

Usetheassemblertosetupadatasegment,stacksegment,andcodesegment.


(cont.)

ChapterObjecves

ShowhowtosetupaprocedureusingPROCandENDP.

Explainthedifferencebetweenmemorymodelsandfull-segmentdefini>onsfortheMASM

assembler.

UsetheVisualonlineassemblertoperformdatamovementtasks.


(cont.)


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41MOVRevisited Inthischapter,theMOVinstruc>onintroduces

machinelanguageinstruc>onsavailablewith

variousaddressingmodesandinstruc>ons.

Itmaybenecessarytointerpretmachinelanguageprogramsgeneratedbyanassembler.

Occasionally,machinelanguagepatchesaremadebyusingtheDEBUGprogramavailable

withDOSandVisualforWindows.

MachineLanguage Na>vebinarycodemicroprocessorusesasits

instruc>onstocontrolitsopera>on.

instruc>onsvaryinlengthfrom1to13bytes Over100,000varia>onsofmachinelanguage

instruc>ons.

thereisnocompletelistofthesevaria>ons Somebitsinamachinelanguageinstruc>onare

given;remainingbitsaredeterminedforeachvaria>onoftheinstruc>on.


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Figure41Theformatsofthe8086Core2instruc>ons.(a)The16-bitformand(b)the32-bitform.

80386andaboveassumeallinstruc>onsare16-bitmodeinstruc>onswhenthemachineisoperatedin

therealmode(DOS).

inprotectedmode(Windows),theupperbyteofthedescriptorcontainstheD-bitthatselectseitherthe16-or32-bitinstruc>onmode

TheOpcode Selectstheopera>on(addi>on,subtrac>on,etc.,)

performedbythemicroprocessor.

either1or2byteslongformostinstruc>ons Figure42illustratesthegeneralformofthefirst

opcodebyteofmanyinstruc>ons.

first6bitsofthefirstbytearethebinaryopcoderemaining2bitsindicatethedirecon(D)ofthedata

flow,andindicatewhetherthedataareabyteoraword(W)


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Figure42Byte1ofmanymachinelanguageinstruc>ons,showingtheposi>onoftheD-andW-bits.#

Figure43Byte2ofmanymachinelanguageinstruc>ons,showingtheposi>onoftheMOD,REG,andR/Mfields.


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MODField Specifiesaddressingmode(MOD)andwhethera

displacementispresentwiththeselectedtype.

IfMODfieldcontainsan11,itselectstheregister-addressingmode

Registeraddressingspecifiesaregisterinsteadofamemoryloca>on,usingtheR/Mfield

IftheMODfieldcontainsa00,01,or10,theR/Mfieldselectsoneofthedatamemory-addressing

modes.

All8-bitdisplacementsaresign-extendedinto16-bitdisplacementswhentheprocessorexecutestheinstruc>on.

ifthe8-bitdisplacementis00H7FH(posi>ve),itissign-extendedto0000H007FHbeforeaddingto

theoffsetaddress

ifthe8-bitdisplacementis80HFFH(nega>ve),itissign-extendedtoFF80HFFFFH

Someassemblerprogramsdonotusethe8-bitdisplacementsandinplacedefaulttoall16-bitdisplacements.


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RegisterAssignments Supposea2-byteinstruc>on,8BECH,appearsina

machinelanguageprogram.

neithera67H(operandaddress-sizeoverrideprefix)nora66H(register-sizeoverrideprefix)appearsasthe

firstbyte,thusthefirstbyteistheopcode

In16-bitmode,thisinstruc>onisconvertedtobinaryandplacedintheinstruc>onformatof

bytes1and2,asillustratedinFigure44.

Figure44The8BECinstruc>onplacedintobytes1and2formatsfromFigures42and43.Thisinstruc>onisaMOVBP,SP.

theopcodeis100010,aMOVinstruc>on

DandWbitsarealogic1,soawordmovesintothedes>na>onregisterspecifiedintheREGfield

REGfieldcontains101,indica>ngregisterBP,sotheMOVinstruc>onmovesdataintoregisterBP


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R/MMemoryAddressing IftheMODfieldcontainsa00,01,or10,theR/M

fieldtakesonanewmeaning.

Figure45illustratesthemachinelanguageversionofthe16-bitinstruc>onMOVDL,[DI]or

instruc>on(8AI5H).

Thisinstruc>onis2byteslongandhasanopcode100010,D=1(toREGfromR/M),W=0(byte),

MOD=00(nodisplacement),REG=010(DL),andR/

M=101([DI]).

Figure45AMOVDL,[DI]instruc>onconvertedtoitsmachinelanguageform.

Iftheinstruc>onchangestoMOVDL,[DI+1],theMODfieldchangesto01for8-bitdisplacement

first2bytesoftheinstruc>onremainthesame instruc>onnowbecomes8A5501Hinsteadof8A15H


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BecausetheMODfieldcontainsa11,theR/Mfieldalsoindicatesaregister.

R/M=100(SP);therefore,thisinstruc>onmovesdatafromSPintoBP.

wrieninsymbolicformasaMOVBP,SPinstruc>on Theassemblerprogramkeepstrackofthe

register-andaddress-sizeprefixesandthemode

ofopera>on.

SpecialAddressingMode Aspecialaddressingmodeoccurswhenmemory

dataarereferencedbyonlythedisplacement

modeofaddressingfor16-bitinstruc>ons.

ExamplesaretheMOV[1000H],DLandMOVNUMB,DLinstruc>ons.

firstinstruc>onmovescontentsofregisterDLintodatasegmentmemoryloca>on1000H

secondmovesregisterDLintosymbolicdatasegmentmemoryloca>onNUMB


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Whenaninstruc>onhasonlyadisplacement,MODfieldisalways00;R/Mfieldalways110.Youcannotactuallyuseaddressingmode[BP]without

adisplacementinmachinelanguage

Iftheindividualtransla>ngthissymbolicinstruc>onintomachinelanguagedoesnotknow

aboutthespecialaddressingmode,the

instruc>onwouldincorrectlytranslatetoaMOV

[BP],DLinstruc>on.

Figure46TheMOV[1000H],DIinstruc>onusesthespecialaddressingmode.#

bitpaernrequiredtoencodetheMOV[1000H],DLinstruc>on

inmachinelanguage


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Figure47TheMOV[BP],DLinstruc>onconvertedtobinarymachinelanguage.

actualformoftheMOV[BP],DLinstruc>on

a3-byteinstruc>onwithadisplacementof00H

32-BitAddressingModes Foundin80386andabove.

byrunningin32-bitinstruc>onmodeorIn16-bitmodebyusingaddress-sizeprefix67H

Ascaled-indexbyteindicatesaddi>onalformsofscaled-indexaddressing.

mainlyusedwhentworegistersareaddedtospecifythememoryaddressinaninstruc>on

Ascaled-indexinstruc>onhas215(32K)possiblecombina>ons.


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Over32,000varia>onsoftheMOVinstruc>onaloneinthe80386-Core2microprocessors.

Figure48showstheformatofthescaled-index

byteasselectedbyavalueof100intheR/Mfield

ofaninstruc>onwhenthe80386andaboveusea

32-bitaddress.

Thele\most2bitsselectascalingfactor(mul>plier)of1x,2x,4x,8x.

Scaled-indexaddressingcanalsouseasingleregistermul>pliedbyascalingfactor.

Figure48Thescaled-indexbyte.

theindexandbasefieldsbothcontainregisternumbers


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AnImmediateInstrucon Anexampleofa16-bitinstruc>onusingimmediateaddressing.

MOVWORDPTR[BX+1000H],1234Hmovesa1234Hintoaword-sizedmemoryloca>onaddressedbysumof1000H,BX,andDSx10H

6-byteinstruc>on2bytesfortheopcode;2bytesarethedataof1234H;

2bytesarethedisplacementof1000H

Figure49showsthebinarybitpaernforeachbyteofthisinstruc>on.

Figure49AMOVWORDPTR,[BX=1000H]1234Hinstruc>onconvertedtobinarymachinelanguage.


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Thisinstruc>on,insymbolicform,includesWORDPTR.direc>veindicatestotheassemblerthatthe

instruc>onusesaword-sizedmemorypointer

Iftheinstruc>onmovesabyteofimmediatedata,BYTEPTRreplacesWORDPTR.

ifadoublewordofimmediatedata,theDWORDPTRdirec>vereplacesBYTEPTR

Instruc>onsreferringtomemorythroughapointerdonotneedtheBYTEPTR,WORDPTR,orDWORDPTRdirec>ves.

SegmentMOVInstrucons Ifcontentsofasegmentregisteraremovedby

MOV,PUSH,orPOPinstruc>ons,aspecialbits(REGfield)selectthesegmentregister.theopcodeforthistypeofMOVinstruc>onisdifferent

forthepriorMOVinstruc>ons

animmediatesegmentregisterMOVisnotavailableintheinstruc>onset

Toloadasegmentregisterwithimmediatedata,firstloadanotherregisterwiththedataandmoveittoasegmentregister.


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Figure410AMOVBX,CSinstruc>onconvertedtobinarymachinelanguage.

Figure410showsaMOVBX,CSinstruc>onconvertedtobinary.

Segmentregisterscanbemovedbetweenany16-bitregisteror16-bitmemoryloca>on.

Aprogramwrieninsymbolicassemblylanguage(assemblylanguage)israrelyassembledbyhandintobinarymachinelanguage.

Anassemblerprogramconvertssymbolicassemblylanguageintomachinelanguage.


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The64-BitModeforthePenum4andCore2

In64-bitmode,aprefixcalledREX(registerextension)isadded.

encodedasa40H4FH,followsotherprefixes;placedimmediatelybeforetheopcode

Purposeistomodifyregandr/mfieldsinthesecondbyteoftheinstruc>on.

REXisneededtobeabletoaddressregistersR8throughR15

Figure411illustratesthestructureandapplica>onofREXtothesecondbyteoftheopcode.

Theregfieldcanonlycontainregisterassignmentsasinothermodesofopera>on

Ther/mfieldcontainseitheraregisterormemoryassignment.

Figure412showsthescaled-indexbytewiththeREXprefixformorecomplexaddressingmodesandalsoforusingascalingfactorinthe64-bit

modeofopera>on.


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Figure411Theapplica>onofREXwithoutscaledindex.#

Figure412Thescaled-indexbyteandREXprefixfor64-bitopera>ons.


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42PUSH/POP Importantinstruc>onsthatstoreandretrievedata

fromtheLIFO(last-in,first-out)stackmemory.

SixformsofthePUSHandPOPinstruc>ons:register,memory,immediatesegmentregister,flags,allregisters

ThePUSHandPOPimmediate&PUSHAandPOPA(allregisters)available80286-Core2.

Registeraddressingallowscontentsofany16-bitregistertotransferto&fromthestack.

Memory-addressingPUSHandPOPinstruc>onsstorecontentsofa16-or32bitmemoryloca>on

onthestackorstackdataintoamemoryloca>on.

Immediateaddressingallowsimmediatedatatobepushedontothestack,butnotpoppedoffthe

stack.


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Segmentregisteraddressingallowscontentsofanysegmentregistertobepushedontothestackorremovedfromthestack.

ESmaybepushed,butdatafromthestackmayneverbepoppedintoES

Theflagsmaybepushedorpoppedfromthatstack.

contentsofallregistersmaybepushedorpopped

PUSH Alwaystransfers2bytesofdatatothestack;

80386andabovetransfer2or4bytes PUSHAinstruc>oncopiescontentsoftheinternal

registerset,exceptthesegmentregisters,tothe

stack.

PUSHA(pushall)instruc>oncopiestheregisterstothestackinthefollowingorder:AX,CX,DX,BX,

SP,BP,SI,andDI.


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PUSHF(pushflags)instruc>oncopiesthecontentsoftheflagregistertothestack.

PUSHADandPOPADinstruc>onspushandpopthecontentsofthe32-bitregistersetin80386-

Pen>um4.

PUSHAandPOPAinstruc>onsdonotfunc>oninthe64-bitmodeofopera>onforthePen>um4

Figure413TheeffectofthePUSHAXinstruc>ononESPandstackmemoryloca>ons37FFHand37FEH.Thisinstruc>onisshownatthepointa\erexecu>on.#


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PUSHAinstruc>onpushesalltheinternal16-bitregistersontothestack,illustratedin414.requires16bytesofstackmemoryspaceto

storealleight16-bitregisters

A\erallregistersarepushed,thecontentsoftheSPregisteraredecrementedby16.

PUSHAisveryusefulwhentheen>reregistersetof80286andabovemustbesaved.

PUSHADinstruc>onplaces32-bitregistersetonthestackin80386-Core2.PUSHADrequires32bytesofstackstorage

Figure414Theopera>onofthePUSHAinstruc>on,showingtheloca>onandorderofstackdata.


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POP Performstheinverseopera>onofPUSH. POPremovesdatafromthestackandplacesitina

target16-bitregister,segmentregister,ora16-bit

memoryloca>on.

notavailableasanimmediatePOP POPF(popflags)removesa16-bitnumberfrom

thestackandplacesitintheflagregister;

POPFDremovesa32-bitnumberfromthestackandplacesitintotheextendedflagregister

POPA(popall)removes16bytesofdatafromthestackandplacesthemintothefollowingregisters,intheordershown:DI,SI,BP,SP,BX,DX,CX,and

AX.

reverseorderfromplacementonthestackbyPUSHAinstruc>on,causingthesamedatatoreturntothe

sameregisters

Figure415showshowthePOPBXinstruc>onremovesdatafromthestackandplacestheminto

registerBX.


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Figure415ThePOPBXinstruc>on,showinghowdataareremovedfromthestack.Thisinstruc>onisshowna\erexecu>on.#

InializingtheStack Whenthestackareaisini>alized,loadboththe

stacksegment(SS)registerandthestackpointer

(SP)register.

Figure416showshowthisvaluecausesdatatobepushedontothetopofthestacksegmentwith

aPUSHCXinstruc>on.

Allsegmentsarecyclicinnaturethetoploca>onofasegmentiscon>guouswiththeboomloca>onofthesegment


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Figure416ThePUSHCXinstruc>on,showingthecyclicalnatureofthestacksegment.Thisinstruc>onis

shownjustbeforeexecu>on,toillustratethatthestackboomiscon>guoustothetop.

Assemblylanguagestacksegmentsetup:firststatementiden>fiesstartofthesegmentlaststatementiden>fiesendofthestacksegment

AssemblerandlinkerprogramsplacecorrectstacksegmentaddressinSSandthelengthofthe

segment(topofthestack)intoSP.

Thereisnoneedtoloadtheseregistersinyourprogram.

unlessyouwishtochangetheini>alvaluesforsomereason


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Ifthestackisnotspecified,awarningwillappearwhentheprogramislinked.

Memorysec>onislocatedintheprogramsegmentprefix(PSP),appendedtothebeginning

ofeachprogramfile.

Ifyouusemorememoryforthestack,youwilleraseinforma>oninthePSP.

informa>oncri>caltotheopera>onofyourprogramandthecomputer

Erroro\encausestheprogramtocrash.

LEA Loadsa16-or32-bitregisterwiththeoffset

addressofthedataspecifiedbytheoperand.

EarlierexamplespresentedbyusingtheOFFSETdirec>ve.

OFFSETperformssamefunc>onasLEAinstruc>oniftheoperandisadisplacement

LEAandMOVwithOFFSETinstruc>onsareboththesamelength(3bytes).


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WhyisLEAinstruc>onavailableifOFFSETaccomplishesthesametask?OFFSETfunc>onswith,andismoreefficientthanLEA

instruc>on,forsimpleoperandssuchasLIST

MicroprocessortakeslongertoexecutetheLEABX,LISTinstruc>ontheMOVBX,OFFSETLIST

TheMOVBX,OFFSETLISTinstruc>onisactuallyassembledasamoveimmediateinstruc>onand

ismoreefficient.

43LOADEFFECTIVEADDRESS LEAinstruc>onloadsany16-bitregisterwiththe

offsetaddress

determinedbytheaddressingmodeselected LDSandLESloada16-bitregisterwithoffset

addressretrievedfromamemoryloca>onthenloadeitherDSorESwithasegment

addressretrievedfrommemory

In80386andabove,LFS,LGS,andLSSareaddedtotheinstruc>onset.


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LDS,LES,LFS,LGS,andLSS Loadany16-or32-bitregisterwithanoffset

address,andtheDS,ES,FS,GS,orSSsegment

registerwithasegmentaddress.

instruc>onsuseanymemory-addressingmodestoaccessa32-bitor48-bitmemorysec>onthat

containbothsegmentandoffsetaddress

Figure417illustratesanexampleLDSBX,[DI]instruc>on.

Figure417TheLDSBX,[DI]instruc>onloadsregisterBXfromaddresses11000Hand11001Hand

registerDSfromloca>ons11002Hand11003H.Thisinstruc>onisshownatthepointjustbeforeDS

changesto3000HandBXchangesto127AH.


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Thisinstruc>ontransfersthe32-bitnumber,addressedbyDIinthedatasegment,intotheBXandDSregisters.

LDS,LES,LFS,LGS,andLSSinstruc>onsobtainanewfaraddressfrommemory.

offsetaddressappearsfirst,followedbythesegmentaddress

Thisformatisusedforstoringall32-bitmemoryaddresses.

Afaraddresscanbestoredinmemorybytheassembler.

Themostusefuloftheloadinstruc>onsistheLSSinstruc>on.

a\erexecu>ngsomedummyinstruc>ons,theoldstackareaisreac>vatedbyloadingbothSSandSP

withtheLSSinstruc>on

CLI(disableinterrupt)andSTI(enableinterrupt)instruc>onsmustbeincludedtodisable

interrupts.


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44STRINGDATATRANSFERS Fivestringdatatransferinstruc>ons:LODS,STOS,

MOVS,INS,andOUTS.

Eachallowsdatatransfersasasinglebyte,word,ordoubleword.

Beforethestringinstruc>onsarepresented,theopera>onoftheDflag-bit(direc>on),DI,andSI

mustbeunderstoodastheyapplytothestring

instruc>ons.

TheDireconFlag Thedirec>onflag(D,locatedintheflagregister)

selectstheauto-incrementortheauto-

decrementopera>onfortheDIandSIregisters

duringstringopera>ons.

usedonlywiththestringinstruc>ons TheCLDinstruc>onclearstheDflagandtheSTD

instruc>onsetsit.

CLDinstruc>onselectstheauto-incrementmodeandSTDselectstheauto-decrementmode


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DIandSI Duringexecu>onofstringinstruc>on,memoryaccessesoccurthroughDIandSIregisters.

DIoffsetaddressaccessesdataintheextrasegmentforallstringinstruc>onsthatuseit

SIoffsetaddressaccessesdatabydefaultinthedatasegment

Opera>ngin32-bitmodeEDIandESIregistersareusedinplaceofDIandSI.

thisallowsstringusinganymemoryloca>onintheen>re4G-byteprotectedmodeaddressspace

LODS LoadsAL,AX,orEAXwithdataatsegmentoffset

addressindexedbytheSIregister.

A1isaddedtoorsubtractedfromSIforabyte-sizedLODS

A2isaddedorsubtractedforaword-sizedLODS. A4isaddedorsubtractedforadoubleword-sized

LODS.

Figure418showstheLODSWinstruc>on.


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Figure418Theopera>onoftheLODSWinstruc>onifDS=1000H,D=0,11000H,11001H=A0.Thisinstruc>onisshowna\erAXisloadedfrommemory,butbeforeSIincrementsby2.#

STOS StoresAL,AX,orEAXattheextrasegment

memoryloca>onaddressedbytheDIregister.

STOSB(storesabyte)storesthebyteinALattheextrasegmentmemoryloca>onaddressedbyDI.

STOSW(storesaword)storesAXinthememoryloca>onaddressedbyDI.

A\erthebyte(AL),word(AX),ordoubleword(EAX)isstored,contentsofDIincrementordecrement.


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STOSwithaREP Therepeatprefix(REP)isaddedtoanystringdatatransferinstruc>onexceptLODS.

REPprefixcausesCXtodecrementby1each>methestringinstruc>onexecutes;a\erCXdecrements,thestringinstruc>onrepeats

IfCXreachesavalueof0,theinstruc>onterminatesandtheprogramcon>nues.

IfCXisloadedwith100andaREPSTOSBinstruc>onexecutes,themicroprocessorautoma>callyrepeatstheSTOSB100>mes.

MOVS Transfersabyte,word,ordoublewordadata

segmentaddressedbySItoextrasegmentloca>onaddressedbySI.pointersareincrementedordecremented,asdictated

bythedirec>onflag

Onlythesourceoperand(SI),locatedinthedatasegmentmaybeoverriddensoanothersegmentmaybeused.

Thedes>na>onoperand(DI)mustalwaysbelocatedintheextrasegment.


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INS Transfersabyte,word,ordoublewordofdatafromanI/Odeviceintotheextrasegment

memoryloca>onaddressedbytheDIregister.I/OaddressiscontainedintheDXregister

UsefulforinpungablockofdatafromanexternalI/Odevicedirectlyintothememory.

Oneapplica>ontransfersdatafromadiskdrivetomemory.

diskdrivesareo\enconsideredandinterfacedasI/Odevicesinacomputersystem

ThreebasicformsoftheINS. INSBinputsdatafroman8-bitI/Odeviceand

storesitinamemoryloca>onindexedbySI.

INSWinstruc>oninputs16-bitI/Odataandstoresitinaword-sizedmemoryloca>on.

INSDinstruc>oninputsadoubleword. Theseinstruc>onscanberepeatedusingtheREP

prefix

allowsanen>reblockofinputdatatobestoredinthememoryfromanI/Odevice


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OUTS Transfersabyte,word,ordoublewordofdata

fromthedatasegmentmemoryloca>onaddress

bySItoanI/Odevice.

I/OdeviceaddressedbytheDXregisteraswiththeINSinstruc>on

Inthe64-bitmodeforPen>um4andCore2,thereisno64-bitoutput

buttheaddressinRSIis64bitswide

45MISCELLANEOUSDATATRANSFER

INSTRUCTIONS

Usedinprograms,datatransferinstruc>onsdetailedinthissec>onareXCHG,LAHF,SAHF,

XLAT,IN,OUT,BSWAP,MOVSX,MOVZX,and

CMOV.


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XCHG Exchangescontentsofaregisterwithanyother

registerormemoryloca>on.

cannotexchangesegmentregistersormemory-to-memorydata

Exchangesarebyte-,word-,ordoublewordanduseanyaddressingmodeexceptimmediate

addressing.

XCHGusingthe16-bitAXregisterwithanother16-bitregister,ismostefficientexchange.

LAHFandSAHF Seldomusedbridgeinstruc>ons. LAHFinstruc>ontransferstherightmost8bitsof

theflagregisterintotheAHregister.

SAHFinstruc>ontransferstheAHregisterintotherightmost8bitsoftheflagregister.

SAHFinstruc>onmayfindsomeapplica>onwiththenumericcoprocessor.

Aslegacyinstruc>ons,theydonotfunc>oninthe64-bitmodeandareinvalidinstruc>ons.


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XLAT ConvertsthecontentsoftheALregisterintoa

numberstoredinamemorytable.

performsthedirecttablelookuptechniqueo\enusedtoconvertonecodetoanother

AnXLATinstruc>onfirstaddsthecontentsofALtoBXtoformamemoryaddresswithinthedata

segment.

copiesthecontentsofthisaddressintoALonlyinstruc>onaddingan8-bittoa16-bitnumber

Figure419Theopera>onoftheXLATinstruc>onatthepointjustbefore6DHisloadedintoAL.


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INandOUT IN&OUTinstruc>onsperformI/Oopera>ons. ContentsofAL,AX,orEAXaretransferredonly

betweenI/Odeviceandmicroprocessor.

anINinstruc>ontransfersdatafromanexternalI/OdeviceintoAL,AX,orEAX

anOUTtransfersdatafromAL,AX,orEAXtoanexternalI/Odevice

Onlythe80386andabovecontainEAX

O\en,instruc>onsarestoredinROM.afixed-portinstruc>onstoredinROMhasitsport

numberpermanentlyfixedbecauseofthenatureof

read-onlymemory

Afixed-portaddressstoredinRAMcanbemodified,butsuchamodifica>ondoesnot

conformtogoodprogrammingprac>ces.

TheportaddressappearsontheaddressbusduringanI/Oopera>on.


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TwoformsofI/Odevice(port)addressing: Fixed-portaddressingallowsdatatransferbetweenAL,AX,orEAXusingan8-bitI/Oport

address.

portnumberfollowstheinstruc>onsopcode Variable-portaddressingallowsdatatransfers

betweenAL,AX,orEAXanda16-bitportaddress.

theI/OportnumberisstoredinregisterDX,whichcanbechanged(varied)duringtheexecu>onof

aprogram.

Figure420Thesignalsfoundinthemicroprocessor-basedsystemforanOUT19H,AXinstruc>on.


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BSWAP Takesthecontentsofany32-bitregisterand

swapsthefirstbytewiththefourth,andthe

secondwiththethird.

BSWAP(byteswap)isavailableonlyin80486Pen>um4microprocessors

Thisinstruc>onisusedtoconvertdatabetweenthebigandlileendianforms.

In64-bitopera>onforthePen>um4,all8bytesintheselectedoperandareswapped.

CMOV Manyvaria>onsoftheCMOVinstruc>on.

thesemovethedataonlyifthecondi>onistrue CMOVZinstruc>onmovesdataonlyiftheresult

fromsomepriorinstruc>onwasazero.

des>na>onislimitedtoonlya16-or32-bitregister,butthesourcecanbea16-or32-bitregisterormemoryloca>on

Becausethisisanewinstruc>on,youcannotuseitwiththeassemblerunlessthe.686switchisaddedtotheprogram


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46SEGMENTOVERRIDEPREFIX Maybeaddedtoalmostanyinstruc>oninanymemory-addressingmode

allowstheprogrammertodeviatefromthedefaultsegment

onlyinstruc>onsthatcannotbeprefixedarejumpandcallinstruc>onsusingthecodesegmentregisterforaddressgenera>on

Addi>onalbyteappendedtothefrontofaninstruc>ontoselectalternatesegmentregister

47ASSEMBLERDETAIL Theassemblercanbeusedtwoways:

withmodelsuniquetoapar>cularassembler withfull-segmentdefini>onsthatallowcompletecontrol

overtheassemblyprocessandareuniversaltoallassemblers

Inmostcases,theinlineassemblerfoundinVisualisusedfordevelopingassemblycodeforuseinaprogram

occasionsrequireseparateassemblymodulesusingtheassembler


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Direcves Indicatehowanoperandorsec>onofaprogramistobeprocessedbytheassembler.

somegenerateandstoreinforma>oninthememory;othersdonot

TheDB(definebyte)direc>vestoresbytesofdatainthememory.

BYTEPTRindicatesthesizeofthedatareferencedbyapointerorindexregister.

Complexsec>onsofassemblycodeares>llwrienusingMASM.

StoringDatainaMemorySegment DB(definebyte),DW(defineword),andDD

(definedoubleword)aremosto\enusedwith

MASMtodefineandstorememorydata.

Ifanumericcoprocessorexecutesso\wareinthesystem,theDQ(definequadword)andDT(define

tenbytes)direc>vesarealsocommon.

Thesedirec>veslabelamemoryloca>onwithasymbolicnameandindicateitssize.


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Memoryisreservedforuseinthefuturebyusingaques>onmark(?)asanoperandforaDB,DW,orDDdirec>ve.

when?isusedinplaceofanumericorASCIIvalue,theassemblersetsasidealoca>onanddoesnot

ini>alizeittoanyspecificvalue

Itisimportantthatword-sizeddataareplacedatwordboundariesanddoubleword-sizeddataare

placedatdoublewordboundaries.

ifnot,themicroprocessorspendsaddi>onal>meaccessingthesedatatypes

ASSUME,EQU,andORG Equatedirec>ve(EQU)equatesanumeric,ASCII,

orlabeltoanotherlabel.

equatesmakeaprogramclearerandsimplifydebugging

TheTHISdirec>vealwaysappearsasTHISBYTE,THISWORD,THISDWORD,orTHISQWORD.

Theassemblercanonlyassigneitherabyte,word,ordoublewordaddresstoalabel.


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TheORG(origin)statementchangesthestar>ngoffsetaddressofthedatainthedatasegmenttoloca>on300H.

At>mes,theoriginofdataorthecodemustbeassignedtoanabsoluteoffsetaddresswiththe

ORGstatement.

ASSUMEtellstheassemblerwhatnameshavebeenchosenforthecode,data,extra,andstack

segments.

PROCandENDP Indicatestartandendofaprocedure(subrou>ne).

theyforcestructurebecausetheprocedureisclearlydefined

Ifstructureistobeviolatedforwhateverreason,usetheCALLF,CALLN,RETF,andRETN

instruc>ons.

BoththePROCandENDPdirec>vesrequirealabeltoindicatethenameoftheprocedure.


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ThePROCdirec>ve,whichindicatesthestartofaprocedure,mustalsobefollowedwithaNEARorFAR.ANEARprocedureisonethatresidesinthesame

codesegmentastheprogram,o\enconsideredtobelocal

AFARproceduremayresideatanyloca>oninthememorysystem,considered global

Thetermglobaldenotesaprocedurethatcanbeusedbyanyprogram.

Localdefinesaprocedurethatisonlyusedbythecurrentprogram.

MemoryOrganizaon Theassemblerusestwobasicformatsfor

developingso\ware:

onemethodusesmodels;theotherusesfull-segmentdefini>ons

MemorymodelsareuniquetoMASM. Themodelsareeasiertouseforsimpletasks. Thefull-segmentdefini>onsofferbeercontrol

overtheassemblylanguagetaskandarerecommendedforcomplexprograms.


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Models TherearemanymodelsavailabletotheMASM

assembler,rangingfrom>nytohuge.

Specialdirec>vessuchas@DATAareusedtoiden>fyvarioussegments.

ModelsareimportantwithbothMicroso\VisualandBorlanddevelopmentsystemsifassembly

languageisincludedwithprograms.

Full-SegmentDefinions Full-segmentdefini>onsarealsousedwiththe

BorlandandMicroso\environmentsfor

d d l d bl l

microprocessors 1 basics

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