单片机外文文献.docx

《单片机外文文献.docx》由会员分享，可在线阅读，更多相关《单片机外文文献.docx（5页珍藏版）》请在课桌文档上搜索。

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.