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1、A:FundamentalsofSingle-chipMicrocomputerThesingle-chipmicrocomputeristheculminationofboththedevelopmentofthedigitalcomputerandtheintegratedcircuitarguablythetowmostsignificantinventionsofthe20thcenturyThesetowtypesofarchitecturearefoundinsingle-chipmicrocomputer.Someemploythesplitprogram/datamemoryo
2、ftheHarvardarchitecture,showninFig.3-5A-1,othersfollowthephilosophy,widelyadaptedforgeneral-purposecomputersandmicroprocessors,ofmakingnologicaldistinctionbetweenProgramanddatamemoryasinthePrincetonarchitecture,showninFig.3-5A-2.Ingeneraltermsasingle-chipmicrocomputerischaracterizedbytheincorporatio
3、nofalltheunitsofacomputerintoasingledevice,asshowninFig3-5A-3.Fig,3-5A-1AHarvardtypeFig3-5A-3.PrincipalfeaturesofamicrocomputerReadonlymemory(ROM)ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicrocomputersandmicrocontrollersareintendedforhigh-volumeapplicationsandhencet
4、heeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybecommittedpermanentlyduringthemanufactureofchips.Clearly,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsystem
5、withahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.SomemanufacturersprovideadditionalROMoptionsbyincludingintheirrangedeviceswith(orintendedforusewith)userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesasana
6、ddressanddatabusforaccessingexternalmemory.ThistypeofdevicecanbehavefunctionallyasthesinglechipmicrocomputerfromWhichitisderivedaIbeitWithrestrictedI/Oandamodifiedexternalcircuit.TheuseoftheseROMlessdevicesiscommoneveninproductioncircuitswherethevolumedoesnotjustifythedevelopmentcostsofcustomon-chip
7、ROM2;therecanstillbeasignificantsavinginI/Oandotherchipscomparedtoaconventionalmicroprocessorbasedcircuit.MoreexactreplacementforROMdevicescanbeobtainedintheformofvariantswith,piggy-back,EPROM(ErasableprogrammableROM)socketsordevicesW汕EPROMinsteadofROM.Thesedevicesarenaturallymoreexpensivethanequiva
8、lentROMdevice,butdoprovidecompIetecircuitequivalents.EPROMbaseddevicesarealsoextremelyattractiveforlow-volumeapplicationswheretheyprovidetheadvantagesofasingle-chipdevice,intermsofon-chipI/O,etc.,withtheconvenienceofflexibleuserprogrammability.Randomaccessmemory(RAM).RAMisforthestorageofworkingvaria
9、blesanddatausedduringprogramexecution.Thesizeofthismemoryvarieswithdevicetypebutithasthesamecharacteristicwidth(4,8,16bitsetc.)astheprocessor,Specialfunctionregisters,suchasstackpointerortimerregisterareoftenlogicallyincorporatedintotheRAMarea.ItisalsocommoninHardtypemicrocomputerstotreattheRAMareaa
10、sacollectionofregister;itisunnecessarytomakedistinctionbetweenRAMandprocessorregisterasisdoneinthecaseofamicroprocessorsystemsinceRAMandregistersarenotusuallyphysicallyseparatedinamicrocomputer.Centralprocessingunit(CPU).TheCPUismuchlikethatofanymicroprocessor.Manyapplicationsofmicrocomputersandmicr
11、ocontrollersinvolvethehandlingofbinary-codeddecimal(BCD)data(fornumericaldisplays,forexample),henceitiscommontofindthattheCPUiswelladaptedtohandlingthistypeofdata.Itisalsocommontofindgoodfacilitiesfortesting,settingandresettingindividualbitsofmemoryorI/Osincemanycontrollerapplicationsinvolvetheturni
12、ngonandoffofsingleoutputlinesorthereadingthesingleline.Theselinesarereadilyinterfacedtotwo-statedevicesSuchasswitches,thermostats,solid-staterelays,valves,motor,etc.Parallelinput/output.Parallelinputandoutputschemesvarysomewhatindifferentmicrocomputer;inmostamechanismisprovidedtoatleastallowsomeflex
13、ibilityofchoosingwhichpinsareoutputsandwhichareinputs.Thismayapplytoallorsomeoftheports.SomeI/Olinesaresuitablefordirectinterfacingto,forexample,fluorescentdisplays,orcanprovidesufficientcurrenttomakeinterfacingothercomponentsstraightforward.SomedevicesallowanI/Oporttobeconfiguredasasystembustoallow
14、off-chipmemoryandI/Oexpansion.Thisfacilityispotentiallyusefulasaproductrangedevelops,Sincesuccessiveenhancementsmaybecometoobigforon-chipmemoryanditisundesirablenottobuildontheexistingsoftwarebase.Serialinput/output.Serialcommunicationwithterminaldevicesiscommonmeansofprovidingalinkusingasmallnumber
15、oflines.Thissortofcommunicationcanalsobeexploitedforinterfacingspecialfunctionchipsorlinkingseveralmicrocomputerstogether.Boththecommonasynchronoussynchronouscommunicationschemesrequireprotocolsthatprovideframing(startandstop)information.ThiscanbeimplementedasahardwarefacilityorU(S)ART(Universal(Syn
16、chronous)asynchronousreceiver/transmitter)relievingtheprocessor(andtheapplicationsprogrammer)ofthislow-level,time-consuming,detail,tismerelynecessarytoselectedabaud-rateandpossiblyotheroptions(numbcrofstopbits,parity,etc.)andload(orreadfrom)theserialtransmitter(orreceiver)buffer.Serializationoftheda
17、taintheappropriateformatisthenhandledbythehardwarecircuit.TimingZcounterfacilities.Manyapplicationofsingle-chipmicrocomputersrequireaccurateevaluationofelapsedrealtime.Thiscanbedeterminedbycarefulassessmentoftheexecutiontimeofeachbranchinaprogrambutthisrapidlybecomesinefficientforallbutsimplestprogr
18、ams.Thepreferredapproachistousetimercircuitthatcanindependentlycountprecisetimeincrementsandgenerateaninterruptafterapresettimehaselapsed.Thistypeoftimerisusuallyarrangedtobereloadablewiththerequiredcount.Thetimerthendecrementsthisvalueproducinganinterruptorsettingaflagwhenthecounterreacheszero.Bett
19、ertimersthenhavetheabilitytoautomaticallyreloadtheinitialcountvalue.Thisrelievestheprogrammeroftheresponsibilityofreloadingthecounterandassessingelapsedlimebeforethetimerrestarted,whichotherwisewoundbenecessaryifcontinuouspreciselytimedinterruptswererequired(asinaclock,fbrexample).Sometimesassociate
20、dwithtimerisaneventcounter.Withthisfacilitythereisusuallyaspecialinputpin,thatcandrivethecounterdirectly.Timingcomponents.Theclockcircuitryofmostmicrocomputersrequiresonlysimpletimingcomponents.Ifmaximumperfbrmanceisrequired,acrystalmustbeusedtoensurethemaximumclockfrequencyisapproachedbutnotexceede
21、d.Manyclockcircuitsalsoworkwitharesistorandcapacitoraslow-costtimingcomponentsorcanbedrivenfromanexternalsource.Thislatterarrangementisusefulisexternalsynchronizationofthemicrocomputerisrequired.B:PLC1PLCs(programmablelogicalcontroller)faceevermorecomplexchallengesthesedays.Whereoncetheyquietlyrepla
22、cedrelaysandgaveanoccasionalreporttoacorporatemainframe,theyarenowgroupedintocells,givennewjobandnewlanguages,andareforcedtocompeteagainstagrowingarrayofcontrolproducts.Forthisyear,sannualPLCtechnologyupdate,wequeriedPLCmakersonthesetopicsandmore.ProgramminglanguagesHigherlevelPLCProgramminglanguage
23、shavebeenaroundforsometime,butlatelytheirpopularityhasmushrooming.,AsRaymondLeveille,vicepresident&generalmanager,SiemensEnergy&Automation.inc;Programmablecontrolsarebeingusedformoreandmoresophisticatedoperations,languagesotherthanladderlogicbecomemorepractical,efficient,andpowerful.Forexample,itsve
24、rydifficulttowriteatrigonometricfunctionusingladderlogic.LanguagesgainingacceptanceincludeBoolean,controlsystemflowcharting,andsuchfunctionchartlanguagesasGraphcetanditsvariation.AndtheresincreasinginterestinlanguageslikeCandBASIC.PLCsinprocesscontrolThusfar,PLCshavenotbeenusedextensivelyforcontinuo
25、usprocesscontrol.Willthiscontinue?Thefeelingthatvegotten,saysKenJannotta,manger,productplanning,seriesOneandSeriesSixproduct,atGEFanucNorthAmerica,isthatPLCSwillbeusedintheprocessindustrybutnotnecessarilyforprocesscontrol.Severalvendors-obviouslybettingthattheoppositewillhappen-haveintroducedPLCSopt
26、imizedforprocessapplication.RichRyan,manger,commercialmarketing,Allen-bradleyProgrammableControlsDiv.,citesPLCssincreasingusesuchindustriesasfood,chemicals,andpetroleum.Ryanfeelstherearetwotypesofapplicationsinwhichtheyreappropriate,one,hesays,iswherethesizeoftheprocesscontrolsystemthatsbeingautomat
27、eddoesntjustifyDCSdistributedcontrolsystem.Withthestartingpricetagsofchoseproductsbeingrelativelyhigh,aprogrammablecontrollermakessenseforsmall,lowloopcountapplication.Thesecondiswhereyouhavetointegratetheloopcloselywiththesequentiallogical.Batchcontrollersareprimeexample,wherethesequenceandmaintain
28、ingtheprocessvariableareintertwinedsocloselythatthebenefitsofhavingaprogrammablecontrollertodothesequentiallogicaloutweighssomeofthedisadvantagesofnothavingadistributedcontrolsystem.BillBarkovitz,presidentofTriconex,predictsthatallfuturecontrollersthatcomeoutintheprocesscontrolsystembusinesswillembr
29、acealotofmorePLCtechnologyandalotmorePLCfunctionalitythantheyeverdidbeforeCommunicationsandMAPCommunicationsarevitaltoanindividualautomationcellandtobeautomatedfactoryasawhole.Wevehearda1olaboutMAPinthe1astfewyears,andalolofcompanieshavejumpedonthebandwagon.2Many,however,weredisappointedwhenafully-d
30、efinedandcompIetedMAPspecificationdidntappearimmediately.SaysLarryKomarek:Rightnow,MAPisStillamovingtargetforthemanufacturers,aspecificalionthatisnotfinal.Presently,forexample.peopleareintroducingproductstomeettheMAP2.1standard.Yet2.1-basedproductswillbeobsoletewhenthenewstandardforMAP3.Oisintroduce
31、d.Becauseofthis,manyPLCvendorsareholdingoffonfullMAPimplementations.Omron,forexample,hasanongoingMAP-Compatibilityprogram;3butFrankNewbum,vicepresidentofOmronsIndustrialDivision,reportsthatbecauseofthelackofafirmdefinition,OmronsPLCsdontyettalktoMAP.Sinceit,sunlikelythatanindividualPLCwouldtalktobro
32、adMAPanyway,makersareconcentratingonproprietarynetworks.AccordingtoSalProvanzano,usersfearthatiftheydogetonboardandvendorswithdrawfromMAP,theyllbetheonesleftholdingacommunicationsstructurethatsnotsupported.UniversalI/OWhilethereareconcernsaboutthelackofcompatiblecommunicationsbetweenPLCsfromdifferen
33、tvendors,theconnectionattheotherend-the1/0-isevenmorefragmented.Withrareexceptions,I/Oisstillproprietary.Yettherearethosewhofeelthat1/0willeventuallybecomemoreuniversal.GEFanucishopingtodothatwithitsGeniussmartI/Oline.TheindependentI/Omakersarepullinginthesamedirection.ManysaythatI/Oissuchahigh-valu
34、eitemthatPLCmakerswillalwayswanttokeepitproprietary.AsKenJannotta,says:TheI/Oisgoingtobeadisproportionateamountofthehardwaresale.CertainlyeachPLCvendorisgoingtotrytoprotectthat.Forthatreason,hesays,PLCmakerswontbeginsellinguniversalI/Osystemfromothervendor.,ifwestartsellingthatkindofproduct,saysjann
35、otta,whatdowemanufacture?WithmoreintelligentI/Oappearing,SalProvanzanofeelsthiswillleadtomoredifferentiationamongI/Ofromdifferentmakers.,WheretheI/Obecomesextremelyintelligentandbecomespartofthesystem,hesays,itreallyishardtodefinewhichistheI/OandwhichisCPU.ItreallyCPU,ifyouwill,isequallyintegratedin
36、tothesystemastheI/O.ConnectingPLCI/OtoPCsWhiledifferentPLCSprobablywillcontinuetouseproprietaryI/O,severalvendorsmakeitpossibletoconnect5theirI/OtoIBMPC-compatibleequipment.Alle-bradeley,Could,andCincinnatiMilacronalreadyhave,andrumorhasitthatGEisplanningsomethingalongthesesamelines.4BillKetelhut,ma
37、nageofproductplanningatGEFanucNorthAmerica,seesthissortofthingasalternativetouniversalI/O.1thinkthetrend,insteadoftowarduniversalI/O,willbemultiplehostinterface,hesaysJodieGlore,directorofmarking,SquareDAutomationProducts,ViewsitasanotherindicationthatPLCSare,andhavebeenforsometime,industrialcompute
38、rs.PLCsVSPCsIftheIBM7552,theActionInstrumentsBC22,andothercomputersareappearingonthefactoryfloor,wontthismeannewcompetitionforPLCs?RichRyan:Therearesomecontrolfunctionsthatarebetterjobsforcomputers.Programmablecontrollershavebeenforcedtofitintothoseapplications.,Yet,themajorityofvendorswesurveyeddon
39、tlikethePCinvasionwillposeaproblemforthem.MostsaidthatPLCSandPCsareenoughapartinarchitecturethattheywillusuallydothecontrol.TheydontfeelthatPCswilltakejobsfromPLCsjustbecausePLCI/OmodulescannowbeconnectedtoPCs;theybelievethissimplymeansthatPLCSandPCswillbeabletosharethesamedata.Thereareinherentarchi
40、tecturaldifferencesbetweenageneralpurposecomputer,saysRichRyan,andaprogrammablecontroller.Therearehardwareconstructsbuiltintoalmosteverymanufacturesprogrammablecontrollertodaythatcustomizethehardwaretorunladderlogicandtosolvemachinecode.Onefundamentaldifferencehecitesiscalledstateofthemachine.Ryan:Whenyoushutthemachineoff,orinterruptthecycle,oryoujumptoanotherspotinthecycle,programmablecontrollersinherentlyrememberthestateofthemachine:whatthetimerswere,whatthecounterswere,whatthestatesofallthelatcheswere.Computersdontinherentlydothat.
