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1、A:FundamentalsofSingle-chipMicrocomputer Thesingle-chipmicrocomputeristheculminationofboththedevelopmentofthedigitalcomputerandtheintegratedcircuitarguablythetowmostsignificantinventionsofthe20thcentury Thesetowtypesofarchitecturearefoundinsingle-chipmicrocomputer.Someemploythesplitprogram/datamemor
2、yoftheHarvardarchitecture,showninFig.3-5A-1,othersfollowthephilosophy,widelyadaptedforgeneral-purposecomputersandmicroprocessors,ofmakingnologicaldistinctionbetweenProgramanddatamemoryasinthePrincetonarchitecture,showninFig.3-5A-2.Ingeneraltermsasingle-chipmicrocomputerischaracterizedbytheincorporat
3、ionofalltheunitsofacomputerintoasingledevice,asshowninFig3-5A-3.Fig,3-5A-1AHarvardtype Fig3-5A-3.PrincipalfeaturesofamicrocomputerReadonlymemory(ROM)ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicrocomputersandmicrocontrollersareintendedforhigh-volumeapplicationsandhen
4、cetheeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybecommittedpermanentlyduringthemanufactureofchips.Clearly,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsys
5、temwithahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.SomemanufacturersprovideadditionalROMoptionsbyincludingintheirrangedeviceswith(orintendedforusewith)userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesas
6、anaddressanddatabusforaccessingexternalmemory.ThistypeofdevicecanbehavefunctionallyasthesinglechipmicrocomputerfromWhichitisderivedaIbeitWithrestrictedI/Oandamodifiedexternalcircuit.TheuseoftheseROMlessdevicesiscommoneveninproductioncircuitswherethevolumedoesnotjustifythedevelopmentcostsofcustomon-c
7、hipROM2;therecanstillbeasignificantsavinginI/Oandotherchipscomparedtoaconventionalmicroprocessorbasedcircuit.MoreexactreplacementforROMdevicescanbeobtainedintheformofvariantswith,piggy-back,EPROM(ErasableprogrammableROM)socketsordevicesW汕EPROMinsteadofROM.Thesedevicesarenaturallymoreexpensivethanequ
8、ivalentROMdevice,butdoprovidecompIetecircuitequivalents.EPROMbaseddevicesarealsoextremelyattractiveforlow-volumeapplicationswheretheyprovidetheadvantagesofasingle-chipdevice,intermsofon-chipI/O,etc.,withtheconvenienceofflexibleuserprogrammability.Randomaccessmemory(RAM).RAMisforthestorageofworkingva
9、riablesanddatausedduringprogramexecution.Thesizeofthismemoryvarieswithdevicetypebutithasthesamecharacteristicwidth(4,8,16bitsetc.)astheprocessor,Specialfunctionregisters,suchasstackpointerortimerregisterareoftenlogicallyincorporatedintotheRAMarea.ItisalsocommoninHardtypemicrocomputerstotreattheRAMar
10、eaasacollectionofregister;itisunnecessarytomakedistinctionbetweenRAMandprocessorregisterasisdoneinthecaseofamicroprocessorsystemsinceRAMandregistersarenotusuallyphysicallyseparatedinamicrocomputer.Centralprocessingunit(CPU).TheCPUismuchlikethatofanymicroprocessor.Manyapplicationsofmicrocomputersandm
11、icrocontrollersinvolvethehandlingofbinary-codeddecimal(BCD)data(fornumericaldisplays,forexample),henceitiscommontofindthattheCPUiswelladaptedtohandlingthistypeofdata.Itisalsocommontofindgoodfacilitiesfortesting,settingandresettingindividualbitsofmemoryorI/Osincemanycontrollerapplicationsinvolvethetu
12、rningonandoffofsingleoutputlinesorthereadingthesingleline.Theselinesarereadilyinterfacedtotwo-statedevicesSuchasswitches,thermostats,solid-staterelays,valves,motor,etc.Parallelinput/output.Parallelinputandoutputschemesvarysomewhatindifferentmicrocomputer;inmostamechanismisprovidedtoatleastallowsomef
13、lexibilityofchoosingwhichpinsareoutputsandwhichareinputs.Thismayapplytoallorsomeoftheports.SomeI/Olinesaresuitablefordirectinterfacingto,forexample,fluorescentdisplays,orcanprovidesufficientcurrenttomakeinterfacingothercomponentsstraightforward.SomedevicesallowanI/Oporttobeconfiguredasasystembustoal
14、lowoff-chipmemoryandI/Oexpansion.Thisfacilityispotentiallyusefulasaproductrangedevelops,Sincesuccessiveenhancementsmaybecometoobigforon-chipmemoryanditisundesirablenottobuildontheexistingsoftwarebase.Serialinput/output.Serialcommunicationwithterminaldevicesiscommonmeansofprovidingalinkusingasmallnum
15、beroflines.Thissortofcommunicationcanalsobeexploitedforinterfacingspecialfunctionchipsorlinkingseveralmicrocomputerstogether.Boththecommonasynchronoussynchronouscommunicationschemesrequireprotocolsthatprovideframing(startandstop)information.ThiscanbeimplementedasahardwarefacilityorU(S)ART(Universal(
16、Synchronous)asynchronousreceiver/transmitter)relievingtheprocessor(andtheapplicationsprogrammer)ofthislow-level,time-consuming,detail,tismerelynecessarytoselectedabaud-rateandpossiblyotheroptions(numbcrofstopbits,parity,etc.)andload(orreadfrom)theserialtransmitter(orreceiver)buffer.Serializationofth
17、edataintheappropriateformatisthenhandledbythehardwarecircuit.TimingZcounterfacilities.Manyapplicationofsingle-chipmicrocomputersrequireaccurateevaluationofelapsedrealtime.Thiscanbedeterminedbycarefulassessmentoftheexecutiontimeofeachbranchinaprogrambutthisrapidlybecomesinefficientforallbutsimplestpr
18、ograms.Thepreferredapproachistousetimercircuitthatcanindependentlycountprecisetimeincrementsandgenerateaninterruptafterapresettimehaselapsed.Thistypeoftimerisusuallyarrangedtobereloadablewiththerequiredcount.Thetimerthendecrementsthisvalueproducinganinterruptorsettingaflagwhenthecounterreacheszero.B
19、ettertimersthenhavetheabilitytoautomaticallyreloadtheinitialcountvalue.Thisrelievestheprogrammeroftheresponsibilityofreloadingthecounterandassessingelapsedlimebeforethetimerrestarted,whichotherwisewoundbenecessaryifcontinuouspreciselytimedinterruptswererequired(asinaclock,fbrexample).Sometimesassoci
20、atedwithtimerisaneventcounter.Withthisfacilitythereisusuallyaspecialinputpin,thatcandrivethecounterdirectly.Timingcomponents.Theclockcircuitryofmostmicrocomputersrequiresonlysimpletimingcomponents.Ifmaximumperfbrmanceisrequired,acrystalmustbeusedtoensurethemaximumclockfrequencyisapproachedbutnotexce
21、eded.Manyclockcircuitsalsoworkwitharesistorandcapacitoraslow-costtimingcomponentsorcanbedrivenfromanexternalsource.Thislatterarrangementisusefulisexternalsynchronizationofthemicrocomputerisrequired.B:PLC1 PLCs(programmablelogicalcontroller)faceevermorecomplexchallengesthesedays.Whereoncetheyquietlyr
22、eplacedrelaysandgaveanoccasionalreporttoacorporatemainframe,theyarenowgroupedintocells,givennewjobandnewlanguages,andareforcedtocompeteagainstagrowingarrayofcontrolproducts.Forthisyear,sannualPLCtechnologyupdate,wequeriedPLCmakersonthesetopicsandmore.Programminglanguages HigherlevelPLCProgramminglan
23、guageshavebeenaroundforsometime,butlatelytheirpopularityhasmushrooming.,AsRaymondLeveille,vicepresident&generalmanager,SiemensEnergy&Automation.inc;Programmablecontrolsarebeingusedformoreandmoresophisticatedoperations,languagesotherthanladderlogicbecomemorepractical,efficient,andpowerful.Forexample,
24、itsverydifficulttowriteatrigonometricfunctionusingladderlogic.LanguagesgainingacceptanceincludeBoolean,controlsystemflowcharting,andsuchfunctionchartlanguagesasGraphcetanditsvariation.AndtheresincreasinginterestinlanguageslikeCandBASIC.PLCsinprocesscontrol Thusfar,PLCshavenotbeenusedextensivelyforco
25、ntinuousprocesscontrol.Willthiscontinue?Thefeelingthatvegotten,saysKenJannotta,manger,productplanning,seriesOneandSeriesSixproduct,atGEFanucNorthAmerica,isthatPLCSwillbeusedintheprocessindustrybutnotnecessarilyforprocesscontrol.Severalvendors-obviouslybettingthattheoppositewillhappen-haveintroducedP
26、LCSoptimizedforprocessapplication.RichRyan,manger,commercialmarketing,Allen-bradleyProgrammableControlsDiv.,citesPLCssincreasingusesuchindustriesasfood,chemicals,andpetroleum.Ryanfeelstherearetwotypesofapplicationsinwhichtheyreappropriate,one,hesays,iswherethesizeoftheprocesscontrolsystemthatsbeinga
27、utomateddoesntjustifyDCSdistributedcontrolsystem.Withthestartingpricetagsofchoseproductsbeingrelativelyhigh,aprogrammablecontrollermakessenseforsmall,lowloopcountapplication.Thesecondiswhereyouhavetointegratetheloopcloselywiththesequentiallogical.Batchcontrollersareprimeexample,wherethesequenceandma
28、intainingtheprocessvariableareintertwinedsocloselythatthebenefitsofhavingaprogrammablecontrollertodothesequentiallogicaloutweighssomeofthedisadvantagesofnothavingadistributedcontrolsystem.BillBarkovitz,presidentofTriconex,predictsthatallfuturecontrollersthatcomeoutintheprocesscontrolsystembusinesswi
29、llembracealotofmorePLCtechnologyandalotmorePLCfunctionalitythantheyeverdidbefore CommunicationsandMAP Communicationsarevitaltoanindividualautomationcellandtobeautomatedfactoryasawhole.Wevehearda1olaboutMAPinthe1astfewyears,andalolofcompanieshavejumpedonthebandwagon.2Many,however,weredisappointedwhen
30、afully-definedandcompIetedMAPspecificationdidntappearimmediately.SaysLarryKomarek:Rightnow,MAPisStillamovingtargetforthemanufacturers,aspecificalionthatisnotfinal.Presently,forexample.peopleareintroducingproductstomeettheMAP2.1standard.Yet2.1-basedproductswillbeobsoletewhenthenewstandardforMAP3.Oisi
31、ntroduced.Becauseofthis,manyPLCvendorsareholdingoffonfullMAPimplementations.Omron,forexample,hasanongoingMAP-Compatibilityprogram;3butFrankNewbum,vicepresidentofOmronsIndustrialDivision,reportsthatbecauseofthelackofafirmdefinition,OmronsPLCsdontyettalktoMAP.Sinceit,sunlikelythatanindividualPLCwouldt
32、alktobroadMAPanyway,makersareconcentratingonproprietarynetworks.AccordingtoSalProvanzano,usersfearthatiftheydogetonboardandvendorswithdrawfromMAP,theyllbetheonesleftholdingacommunicationsstructurethatsnotsupported.UniversalI/O WhilethereareconcernsaboutthelackofcompatiblecommunicationsbetweenPLCsfro
33、mdifferentvendors,theconnectionattheotherend-the1/0-isevenmorefragmented.Withrareexceptions,I/Oisstillproprietary.Yettherearethosewhofeelthat1/0willeventuallybecomemoreuniversal.GEFanucishopingtodothatwithitsGeniussmartI/Oline.TheindependentI/Omakersarepullinginthesamedirection.ManysaythatI/Oissucha
34、high-valueitemthatPLCmakerswillalwayswanttokeepitproprietary.AsKenJannotta,says:TheI/Oisgoingtobeadisproportionateamountofthehardwaresale.CertainlyeachPLCvendorisgoingtotrytoprotectthat.Forthatreason,hesays,PLCmakerswontbeginsellinguniversalI/Osystemfromothervendor.,ifwestartsellingthatkindofproduct
35、,saysjannotta,whatdowemanufacture?WithmoreintelligentI/Oappearing,SalProvanzanofeelsthiswillleadtomoredifferentiationamongI/Ofromdifferentmakers.,WheretheI/Obecomesextremelyintelligentandbecomespartofthesystem,hesays,itreallyishardtodefinewhichistheI/OandwhichisCPU.ItreallyCPU,ifyouwill,isequallyint
36、egratedintothesystemastheI/O.ConnectingPLCI/OtoPCs WhiledifferentPLCSprobablywillcontinuetouseproprietaryI/O,severalvendorsmakeitpossibletoconnect5theirI/OtoIBM PC-compatible equipment.Alle-bradeley,Could,andCincinnati Milacronalreadyhave,andrumorhasitthatGEisplanningsomethingalongthesesamelines.4Bi
37、llKetelhut,manageofproductplanningatGEFanucNorthAmerica,seesthissortofthingasalternativetouniversalI/O.1thinkthetrend,insteadoftowarduniversalI/O,willbemultiplehostinterface,hesaysJodieGlore,directorofmarking,SquareDAutomationProducts,ViewsitasanotherindicationthatPLCSare,andhavebeenforsometime,indu
38、strialcomputers.PLCsVSPCs IftheIBM7552,theActionInstrumentsBC22,andothercomputersareappearingonthefactoryfloor,wontthismeannewcompetitionforPLCs?RichRyan:Therearesomecontrolfunctionsthatarebetterjobsforcomputers.Programmablecontrollershavebeenforcedtofitintothoseapplications.,Yet,themajorityofvendor
39、swesurveyeddontlikethePCinvasionwillposeaproblemforthem.MostsaidthatPLCSandPCsareenoughapartinarchitecturethattheywillusuallydothecontrol.TheydontfeelthatPCswilltakejobsfromPLCsjustbecausePLCI/OmodulescannowbeconnectedtoPCs;theybelievethissimplymeansthatPLCSandPCswillbeabletosharethesamedata.Therear
40、einherentarchitecturaldifferencesbetweenageneralpurposecomputer,saysRichRyan,andaprogrammablecontroller.Therearehardwareconstructsbuiltintoalmosteverymanufacturesprogrammablecontrollertodaythatcustomizethehardwaretorunladderlogicandtosolvemachinecode.Onefundamentaldifferencehecitesiscalledstateofthemachine.Ryan:Whenyoushutthemachineoff,orinterruptthecycle,oryoujumptoanotherspotinthecycle,programmablecontrollersinherentlyrememberthestateofthemachine:whatthetimerswere,whatthecounterswere,whatthestatesofallthelatcheswere.Computersdontinherentlydothat.
