3电气工程及其自动化专业 外文文献 英文文献 外文翻译 plc方面Word下载.docx

3电气工程及其自动化专业 外文文献 英文文献 外文翻译 plc方面Word下载.docx

《3电气工程及其自动化专业 外文文献 英文文献 外文翻译 plc方面Word下载.docx》由会员分享，可在线阅读，更多相关《3电气工程及其自动化专业 外文文献 英文文献 外文翻译 plc方面Word下载.docx（9页珍藏版）》请在冰豆网上搜索。

Ingeneraltermsasingle-chipmicroputerischaracterizedbytheincorporationofalltheunitsofaputerintoasingledevice,asshowninFig3-5A-3.

Fig.3-5A-1AHarvardtype

Fig.3-5A-2.AconventionalPrincetonputer

Reset

Interrupts

Power

Fig3-5A-3.Principalfeaturesofamicroputer

Readonlymemory（ROM）.ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicroputersandmicrocontrollersareintendedforhigh-volumeapplicationsandhencetheeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybemittedpermanentlyduringthemanufactureofchips.Clearly,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsystemwithahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.

SomemanufacturersprovideadditionalROMoptionsbyincludingintheirrangedeviceswith（orintendedforusewith）userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesasanaddressanddatabusforaccessingexternalmemory.ThistypeofdevicecanbehavefunctionallyasthesinglechipmicroputerfromwhichitisderivedalbeitwithrestrictedI/Oandamodifiedexternalcircuit.TheuseoftheseROMlessdevicesismoneveninproductioncircuitswherethevolumedoesnotjustifythedevelopmentcostsofcustomon-chipROM[2];

therecanstillbeasignificantsavinginI/Oandotherchipsparedtoaconventionalmicroprocessorbasedcircuit.MoreexactreplacementforROMdevicescanbeobtainedintheformofvariantswith'

piggy-back'

EPROM（ErasableprogrammableROM）socketsordeviceswithEPROMinsteadofROM。

ThesedevicesarenaturallymoreexpensivethanequivalentROMdevice,butdoprovidepletecircuitequivalents.EPROMbaseddevicesarealsoextremelyattractiveforlow-volumeapplicationswheretheyprovidetheadvantagesofasingle-chipdevice,intermsofon-chipI/O,etc.,withtheconvenienceofflexibleuserprogrammability.

Randomaccessmemory（RAM）.RAMisforthestorageofworkingvariablesanddatausedduringprogramexecution.Thesizeofthismemoryvarieswithdevicetypebutithasthesamecharacteristicwidth（4,8,16bitsetc.）astheprocessor,Specialfunctionregisters,suchasstackpointerortimerregisterareoftenlogicallyincorporatedintotheRAMarea.ItisalsomoninHarardtypemicroputerstotreattheRAMareaasacollectionofregister;

itisunnecessarytomakedistinctionbetweenRAMandprocessorregisterasisdoneinthecaseofamicroprocessorsystemsinceRAMandregistersarenotusuallyphysicallyseparatedinamicroputer.

Centralprocessingunit（CPU）.TheCPUismuchlikethatofanymicroprocessor.Manyapplicationsofmicroputersandmicrocontrollersinvolvethehandlingofbinary-codeddecimal（BCD）data（fornumericaldisplays,forexample）,henceitismontofindthattheCPUiswelladaptedtohandlingthistypeofdata.Itisalsomontofindgoodfacilitiesfortesting,settingandresettingindividualbitsofmemoryorI/Osincemanycontrollerapplicationsinvolvetheturningonandoffofsingleoutputlinesorthereadingthesingleline.Theselinesarereadilyinterfacedtotwo-statedevicessuchasswitches,thermostats,solid-staterelays,valves,motor,etc.

Parallelinput/output.Parallelinputandoutputschemesvarysomewhatindifferentmicroputer;

inmostamechanismisprovidedtoatleastallowsomeflexibilityofchoosingwhichpinsareoutputsandwhichareinputs.Thismayapplytoallorsomeoftheports.SomeI/Olinesaresuitablefordirectinterfacingto,forexample,fluorescentdisplays,orcanprovidesufficientcurrenttomakeinterfacingotherponentsstraightforward.SomedevicesallowanI/Oporttobeconfiguredasasystembustoallowoff-chipmemoryandI/Oexpansion.Thisfacilityispotentiallyusefulasaproductrangedevelops,sincesuccessiveenhancementsmaybeetoobigforon-chipmemoryanditisundesirablenottobuildontheexistingsoftwarebase.

Serialinput/output.Serialmunicationwithterminaldevicesismonmeansofprovidingalinkusingasmallnumberoflines.Thissortofmunicationcanalsobeexploitedforinterfacingspecialfunctionchipsorlinkingseveralmicroputerstogether.Boththemonasynchronoussynchronousmunicationschemesrequireprotocolsthatprovideframing（startandstop）information.ThiscanbeimplementedasahardwarefacilityorU（S）ART（Universal（synchronous）asynchronousreceiver/transmitter）relievingtheprocessor（andtheapplicationsprogrammer）ofthislow-level,time-consuming,detail.tismerelynecessarytoselectedabaud-rateandpossiblyotheroptions（numberofstopbits,parity,etc.）andload（orreadfrom）theserialtransmitter（orreceiver）buffer.Serializationofthedataintheappropriateformatisthenhandledbythehardwarecircuit.

Timing/counterfacilities.Manyapplicationofsingle-chipmicroputersrequireaccurateevaluationofelapsedrealtime.Thiscanbedeterminedbycarefulassessmentoftheexecutiontimeofeachbranchinaprogrambutthisrapidlybeesinefficientforallbutsimplestprograms.Thepreferredapproachistousetimercircuitthatcanindependentlycountprecisetimeincrementsandgenerateaninterruptafterapresettimehaselapsed.Thistypeoftimerisusuallyarrangedtobereloadablewiththerequiredcount.Thetimerthendecrementsthisvalueproducinganinterruptorsettingaflagwhenthecounterreacheszero.Bettertimersthenhavetheabilitytoautomaticallyreloadtheinitialcountvalue.Thisrelievestheprogrammeroftheresponsibilityofreloadingthecounterandassessingelapsedtimebeforethetimerrestarted,whichotherwisewoundbenecessaryifcontinuouspreciselytimedinterruptswererequired（asinaclock,forexample）.Sometimesassociatedwithtimerisaneventcounter.Withthisfacilitythereisusuallyaspecialinputpin,thatcandrivethecounterdirectly.

Timingponents.Theclockcircuitryofmostmicroputersrequiresonlysimpletimingponents.Ifmaximumperformanceisrequired,acrystalmustbeusedtoensurethemaximumclockfrequencyisapproachedbutnotexceeded.Manyclockcircuitsalsoworkwitharesistorandcapacitoraslow-costtimingponentsorcanbedrivenfromanexternalsource.Thislatterarrangementisusefulisexternalsynchronizationofthemicroputerisrequired.

WORDSANDTERMS

culminationn.顶点

volatilen.易变的

socketn.插座

B:

PLC[1]

PLCs（programmablelogicalcontroller）faceevermoreplexchallengesthesedays.Whereoncetheyquietlyreplacedrelaysandgaveanoccasionalreporttoacorporatemainframe,theyarenowgroupedintocells,givennewjobandnewlanguages,andareforcedtopeteagainstagrowingarrayofcontrolproducts.Forthisyear'

sannualPLCtechnologyupdate,wequeriedPLCmakersonthesetopicsandmore.

Programminglanguages

HigherlevelPLCprogramminglanguageshavebeenaroundforsometime,butlatelytheirpopularityhasmushrooming."

AsRaymondLeveille,vicepresident&

generalmanager,SiemensEnergy&

Automation.inc;

Programmablecontrolsarebeingusedformoreandmoresophisticatedoperations,languagesotherthanladderlogicbeemorepractical,efficient,andpowerful.Forexample,it'

sverydifficulttowriteatrigonometricfunctionusingladderlogic."

LanguagesgainingacceptanceincludeBoolean,controlsystemflowcharting,andsuchfunctionchartlanguagesasGraphcetanditsvariation.Andthere'

sincreasinginterestinlanguageslikeCandBASIC.

PLCsinprocesscontrol

Thusfar,PLCshavenotbeenusedextensivelyforcontinuousprocesscontrol.Willthiscontinue?

"

ThefeelingthatI'

vegotten,"

saysKenJannotta,manger,productplanning,seriesOneandSeriesSixproduct,atGEFanucNorthAmerica,'

isthatPLCswillbeusedintheprocessindustrybutnotnecessarilyforprocesscontrol."

Severalvendors-obviouslybettingthattheoppositewillhappen-haveintroducedPLCsoptimizedforprocessapplication.RichRyan,manger,mercialmarketing,Allen-bradleyProgrammableControlsDiv.,citesPLCs'

sincreasingusesuchindustriesasfood,chemicals,andpetroleum.Ryanfeelstherearetwotypesofapplicationsinwhichthey'

reappropriate."

one,"

hesays,"

iswherethesizeoftheprocesscontrolsystemthat'

sbeingautomateddoesn'

tjustifyDCS[distributedcontrolsystem].Withthestartingpricetagsofchoseproductsbeingrelativelyhigh,aprogrammablecontrollermakessenseforsmall,lowloopcountapplication.Thesecondiswhereyouhavetointegratetheloopcloselywiththesequentiallogical.Batchcontrollersareprimeexample,wherethesequenceandmaintainingtheprocessvariableareintertwinedsocloselythatthebenefitsofhavingaprogrammablecontrollertodothesequentiallogicaloutweighssomeofthedisadvantagesofnothavingadistributedcontrolsystem."

BillBarkovitz,presidentofTriconex,predictsthat"

allfuturecontrollerstha