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A:FundamentalsofSingle-chipMicrocomputer Thesingle-chipmicrocomputeristheculminationofboththedevelopmentofthedigitalcomputerandtheintegratedcircuitarguablythetowmostsignificantinventionsofthe20thcentury Thesetowtypesofarchitecturearefoundinsingle-chipmicrocomputer.Someemploythesplitprogram/datamemoryoftheHarvardarchitecture,showninFig.3-5A-1,othersfollowthephilosophy,widelyadaptedforgeneral-purposecomputersandmicroprocessors,ofmakingnologicaldistinctionbetweenProgramanddatamemoryasinthePrincetonarchitecture,showninFig.3-5A-2.Ingeneraltermsasingle-chipmicrocomputerischaracterizedbytheincorporationofalltheunitsofacomputerintoasingledevice,asshowninFig3-5A-3.Fig,3-5A-1AHarvardtype Fig3-5A-3.PrincipalfeaturesofamicrocomputerReadonlymemory(ROM)ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicrocomputersandmicrocontrollersareintendedforhigh-volumeapplicationsandhencetheeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybecommittedpermanentlyduringthemanufactureofchips.Clearly,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsystemwithahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.SomemanufacturersprovideadditionalROMoptionsbyincludingintheirrangedeviceswith(orintendedforusewith)userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesasanaddressanddatabusforaccessingexternalmemory.ThistypeofdevicecanbehavefunctionallyasthesinglechipmicrocomputerfromWhichitisderivedaIbeitWithrestrictedI/Oandamodifiedexternalcircuit.TheuseoftheseROMlessdevicesiscommoneveninproductioncircuitswherethevolumedoesnotjustifythedevelopmentcostsofcustomon-chipROM2;therecanstillbeasignificantsavinginI/Oandotherchipscomparedtoaconventionalmicroprocessorbasedcircuit.MoreexactreplacementforROMdevicescanbeobtainedintheformofvariantswith,piggy-back,EPROM(ErasableprogrammableROM)socketsordevicesW汕EPROMinsteadofROM.ThesedevicesarenaturallymoreexpensivethanequivalentROMdevice,butdoprovidecompIetecircuitequivalents.EPROMbaseddevicesarealsoextremelyattractiveforlow-volumeapplicationswheretheyprovidetheadvantagesofasingle-chipdevice,intermsofon-chipI/O,etc.,withtheconvenienceofflexibleuserprogrammability.Randomaccessmemory(RAM).RAMisforthestorageofworkingvariablesanddatausedduringprogramexecution.Thesizeofthismemoryvarieswithdevicetypebutithasthesamecharacteristicwidth(4,8,16bitsetc.)astheprocessor,Specialfunctionregisters,suchasstackpointerortimerregisterareoftenlogicallyincorporatedintotheRAMarea.ItisalsocommoninHardtypemicrocomputerstotreattheRAMareaasacollectionofregister;itisunnecessarytomakedistinctionbetweenRAMandprocessorregisterasisdoneinthecaseofamicroprocessorsystemsinceRAMandregistersarenotusuallyphysicallyseparatedinamicrocomputer.Centralprocessingunit(CPU).TheCPUismuchlikethatofanymicroprocessor.Manyapplicationsofmicrocomputersandmicrocontrollersinvolvethehandlingofbinary-codeddecimal(BCD)data(fornumericaldisplays,forexample),henceitiscommontofindthattheCPUiswelladaptedtohandlingthistypeofdata.Itisalsocommontofindgoodfacilitiesfortesting,settingandresettingindividualbitsofmemoryorI/Osincemanycontrollerapplicationsinvolvetheturningonandoffofsingleoutputlinesorthereadingthesingleline.Theselinesarereadilyinterfacedtotwo-statedevicesSuchasswitches,thermostats,solid-staterelays,valves,motor,etc.Parallelinput/output.Parallelinputandoutputschemesvarysomewhatindifferentmicrocomputer;inmostamechanismisprovidedtoatleastallowsomeflexibilityofchoosingwhichpinsareoutputsandwhichareinputs.Thismayapplytoallorsomeoftheports.SomeI/Olinesaresuitablefordirectinterfacingto,forexample,fluorescentdisplays,orcanprovidesufficientcurrenttomakeinterfacingothercomponentsstraightforward.SomedevicesallowanI/Oporttobeconfiguredasasystembustoallowoff-chipmemoryandI/Oexpansion.Thisfacilityispotentiallyusefulasaproductrangedevelops,Sincesuccessiveenhancementsmaybecometoobigforon-chipmemoryanditisundesirablenottobuildontheexistingsoftwarebase.Serialinput/output.Serialcommunicationwithterminaldevicesiscommonmeansofprovidingalinkusingasmallnumberoflines.Thissortofcommunicationcanalsobeexploitedforinterfacingspecialfunctionchipsorlinkingseveralmicrocomputerstogether.Boththecommonasynchronoussynchronouscommunicationschemesrequireprotocolsthatprovideframing(startandstop)information.ThiscanbeimplementedasahardwarefacilityorU(S)ART(Universal(Synchronous)asynchronousreceiver/transmitter)relievingtheprocessor(andtheapplicationsprogrammer)ofthislow-level,time-consuming,detail,tismerelynecessarytoselectedabaud-rateandpossiblyotheroptions(numbcrofstopbits,parity,etc.)andload(orreadfrom)theserialtransmitter(orreceiver)buffer.Serializationofthedataintheappropriateformatisthenhandledbythehardwarecircuit.TimingZcounterfacilities.Manyapplicationofsingle-chipmicrocomputersrequireaccurateevaluationofelapsedrealtime.Thiscanbedeterminedbycarefulassessmentoftheexecutiontimeofeachbranchinaprogrambutthisrapidlybecomesinefficientforallbutsimplestprograms.Thepreferredapproachistousetimercircuitthatcanindependentlycountprecisetimeincrementsandgenerateaninterruptafterapresettimehaselapsed.Thistypeoftimerisusuallyarrangedtobereloadablewiththerequiredcount.Thetimerthendecrementsthisvalueproducinganinterruptorsettingaflagwhenthecounterreacheszero.Bettertimersthenhavetheabilitytoautomaticallyreloadtheinitialcountvalue.Thisrelievestheprogrammeroftheresponsibilityofreloadingthecounterandassessingelapsedlimebeforethetimerrestarted,whichotherwisewoundbenecessaryifcontinuouspreciselytimedinterruptswererequired(asinaclock,fbrexample).Sometimesassociatedwithtimerisaneventcounter.Withthisfacilitythereisusuallyaspecialinputpin,thatcandrivethecounterdirectly.Timingcomponents.Theclockcircuitryofmostmicrocomputersrequiresonlysimpletimingcomponents.Ifmaximumperfbrmanceisrequired,acrystalmustbeusedtoensurethemaximumclockfrequencyisapproachedbutnotexceeded.Manyclockcircuitsalsoworkwitharesistorandcapacitoraslow-costtimingcomponentsorcanbedrivenfromanexternalsource.Thislatterarrangementisusefulisexternalsynchronizationofthemicrocomputerisrequired.B:PLC1 PLCs(programmablelogicalcontroller)faceevermorecomplexchallengesthesedays.Whereoncetheyquietlyreplacedrelaysandgaveanoccasionalreporttoacorporatemainframe,theyarenowgroupedintocells,givennewjobandnewlanguages,andareforcedtocompeteagainstagrowingarrayofcontrolproducts.Forthisyear,sannualPLCtechnologyupdate,wequeriedPLCmakersonthesetopicsandmore.Programminglanguages HigherlevelPLCProgramminglanguageshavebeenaroundforsometime,butlatelytheirpopularityhasmushrooming.,AsRaymondLeveille,vicepresident&generalmanager,SiemensEnergy&Automation.inc;Programmablecontrolsarebeingusedformoreandmoresophisticatedoperations,languagesotherthanladderlogicbecomemorepractical,efficient,andpowerful.Forexample,itsverydifficulttowriteatrigonometricfunctionusingladderlogic.LanguagesgainingacceptanceincludeBoolean,controlsystemflowcharting,andsuchfunctionchartlanguagesasGraphcetanditsvariation.AndtheresincreasinginterestinlanguageslikeCandBASIC.PLCsinprocesscontrol Thusfar,PLCshavenotbeenusedextensivelyforcontinuousprocesscontrol.Willthiscontinue?Thefeelingthatvegotten,saysKenJannotta,manger,productplanning,seriesOneandSeriesSixproduct,atGEFanucNorthAmerica,isthatPLCSwillbeusedintheprocessindustrybutnotnecessarilyforprocesscontrol.Severalvendors-obviouslybettingthattheoppositewillhappen-haveintroducedPLCSoptimizedforprocessapplication.RichRyan,manger,commercialmarketing,Allen-bradleyProgrammableControlsDiv.,citesPLCssincreasingusesuchindustriesasfood,chemicals,andpetroleum.Ryanfeelstherearetwotypesofapplicationsinwhichtheyreappropriate,one,hesays,iswherethesizeoftheprocesscontrolsystemthatsbeingautomateddoesntjustifyDCSdistributedcontrolsystem.Withthestartingpricetagsofchoseproductsbeingrelativelyhigh,aprogrammablecontrollermakessenseforsmall,lowloopcountapplication.Thesecondiswhereyouhavetointegratetheloopcloselywiththesequentiallogical.Batchcontrollersareprimeexample,wherethesequenceandmaintainingtheprocessvariableareintertwinedsocloselythatthebenefitsofhavingaprogrammablecontrollertodothesequentiallogicaloutweighssomeofthedisadvantagesofnothavingadistributedcontrolsystem.BillBarkovitz,presidentofTriconex,predictsthatallfuturecontrollersthatcomeoutintheprocesscontrolsystembusinesswillembracealotofmorePLCtechnologyandalotmorePLCfunctionalitythantheyeverdidbefore CommunicationsandMAP Communicationsarevitaltoanindividualautomationcellandtobeautomatedfactoryasawhole.Wevehearda1olaboutMAPinthe1astfewyears,andalolofcompanieshavejumpedonthebandwagon.2Many,however,weredisappointedwhenafully-definedandcompIetedMAPspecificationdidntappearimmediately.SaysLarryKomarek:Rightnow,MAPisStillamovingtargetforthemanufacturers,aspecificalionthatisnotfinal.Presently,forexample.peopleareintroducingproductstomeettheMAP2.1standard.Yet2.1-basedproductswillbeobsoletewhenthenewstandardforMAP3.Oisintroduced.Becauseofthis,manyPLCvendorsareholdingoffonfullMAPimplementations.Omron,forexample,hasanongoingMAP-Compatibilityprogram;3butFrankNewbum,vicepresidentofOmronsIndustrialDivision,reportsthatbecauseofthelackofafirmdefinition,OmronsPLCsdontyettalktoMAP.Sinceit,sunlikelythatanindividualPLCwouldtalktobroadMAPanyway,makersareconcentratingonproprietarynetworks.AccordingtoSalProvanzano,usersfearthatiftheydogetonboardandvendorswithdrawfromMAP,theyllbetheonesleftholdingacommunicationsstructurethatsnotsupported.UniversalI/O WhilethereareconcernsaboutthelackofcompatiblecommunicationsbetweenPLCsfromdifferentvendors,theconnectionattheotherend-the1/0-isevenmorefragmented.Withrareexceptions,I/Oisstillproprietary.Yettherearethosewhofeelthat1/0willeventuallybecomemoreuniversal.GEFanucishopingtodothatwithitsGeniussmartI/Oline.TheindependentI/Omakersarepullinginthesamedirection.ManysaythatI/Oissuchahigh-valueitemthatPLCmakerswillalwayswanttokeepitproprietary.AsKenJannotta,says:TheI/Oisgoingtobeadisproportionateamountofthehardwaresale.CertainlyeachPLCvendorisgoingtotrytoprotectthat.Forthatreason,hesays,PLCmakerswontbeginsellinguniversalI/Osystemfromothervendor.,ifwestartsellingthatkindofproduct,saysjannotta,whatdowemanufacture?WithmoreintelligentI/Oappearing,SalProvanzanofeelsthiswillleadtomoredifferentiationamongI/Ofromdifferentmakers.,WheretheI/Obecomesextremelyintelligentandbecomespartofthesystem,hesays,itreallyishardtodefinewhichistheI/OandwhichisCPU.ItreallyCPU,ifyouwill,isequallyintegratedintothesystemastheI/O.ConnectingPLCI/OtoPCs WhiledifferentPLCSprobablywillcontinuetouseproprietaryI/O,severalvendorsmakeitpossibletoconnect5theirI/OtoIBM PC-compatible equipment.Alle-bradeley,Could,andCincinnati Milacronalreadyhave,andrumorhasitthatGEisplanningsomethingalongthesesamelines.4BillKetelhut,manageofproductplanningatGEFanucNorthAmerica,seesthissortofthingasalternativetouniversalI/O.1thinkthetrend,insteadoftowarduniversalI/O,willbemultiplehostinterface,hesaysJodieGlore,directorofmarking,SquareDAutomationProducts,ViewsitasanotherindicationthatPLCSare,andhavebeenforsometime,industrialcomputers.PLCsVSPCs IftheIBM7552,theActionInstrumentsBC22,andothercomputersareappearingonthefactoryfloor,wontthismeannewcompetitionforPLCs?RichRyan:Therearesomecontrolfunctionsthatarebetterjobsforcomputers.Programmablecontrollershavebeenforcedtofitintothoseapplications.,Yet,themajorityofvendorswesurveyeddontlikethePCinvasionwillposeaproblemforthem.MostsaidthatPLCSandPCsareenoughapartinarchitecturethattheywillusuallydothecontrol.TheydontfeelthatPCswilltakejobsfromPLCsjustbecausePLCI/OmodulescannowbeconnectedtoPCs;theybelievethissimplymeansthatPLCSandPCswillbeabletosharethesamedata.Thereareinherentarchitecturaldifferencesbetweenageneralpurposecomputer,saysRichRyan,andaprogrammablecontroller.Therearehardwareconstructsbuiltintoalmosteverymanufacturesprogrammablecontrollertodaythatcustomizethehardwaretorunladderlogicandtosolvemachinecode.Onefundamentaldifferencehecitesiscalledstateofthemachine.Ryan:Whenyoushutthemachineoff,orinterruptthecycle,oryoujumptoanotherspotinthecycle,programmablecontrollersinherentlyrememberthestateofthemachine:whatthetimerswere,whatthecounterswere,whatthestatesofallthelatcheswere.Computersdontinherentlydothat.