温室大棚控制系统外文翻译.doc
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1、外文文献及译文 学院:电气与控制工程学院 班级:测控技术与仪器1002班 姓名: 学号: 指导老师:Thesingle-chipmicrocomputeristheculminationofboththedevelopmentofthedigitalcomputerandtheintegratedcircuitarguablythetowmostsignificantinventionsofthe20thcentury.Thesetowtypesofarchitecturearefoundinsingle-chipmicrocomputer.Someemploythesplitprogram/
2、datamemoryoftheHarvardarchitecture,othersfollowthephilosophy,widelyadaptedforgeneral-purposecomputersandmicroprocessors,ofmakingnologicaldistinctionbetweenprogramanddatamemoryasinthePrincetonarchitecture.Ingeneraltermsasingle-chipmicrocomputerischaracterizedbytheincorporationofalltheunitsofacomputer
3、intoasingledevice.ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicrocomputersandmicrocontrollersareintendedforhigh-volumeapplicationsandhencetheeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybecommittedpermanentlyduringthemanufactureofchips.Cl
4、early,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsystemwithahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.SomemanufacturersprovideadditionalROMoptionsbyincludingint
5、heirrangedeviceswith(orintendedforusewith)userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesasanaddressanddatabusforaccessingexternalmemory.Thistypeofdevicecanbehavefunctionallyasthesinglechipmicrocomputerfromwhichitisderived
6、albeitwithrestrictedI/Oandamodifiedexternalcircuit.TheuseoftheseROMlessdevicesiscommoneveninproductioncircuitswherethevolumedoesnotjustifythedevelopmentcostsofcustomon-chipROM;therecanstillbeasignificantsavinginI/Oandotherchipscomparedtoaconventionalmicroprocessorbasedcircuit.Moreexactreplacementfor
7、ROMdevicescanbeobtainedintheformofvariantswithpiggy-backEPROM(ErasableprogrammableROM)socketsordeviceswithEPROMinsteadofROM.ThesedevicesarenaturallymoreexpensivethanequivalentROMdevice,butdoprovidecompletecircuitequivalents.EPROMbaseddevicesarealsoextremelyattractiveforlow-volumeapplicationswherethe
8、yprovidetheadvantagesofasingle-chipdevice,intermsofon-chipI/O,etc.,withtheconvenienceofflexibleuserprogrammability.TheCPUismuchlikethatofanymicroprocessor.Manyapplicationsofmicrocomputersandmicrocontrollersinvolvethehandlingofbinary-codeddecimal(BCD)data(fornumericaldisplays,forexample),henceitiscom
9、montofindthattheCPUiswelladaptedtohandlingthistypeofdata.Itisalsocommontofindgoodfacilitiesfortesting,settingandresettingindividualbitsofmemoryorI/Osincemanycontrollerapplicationsinvolvetheturningonandoffofsingleoutputlinesorthereadingthesingleline.Theselinesarereadilyinterfacedtotwo-statedevicessuc
10、hasswitches,thermostats,solid-staterelays,valves,motor,etc.Parallelinputandoutputschemesvarysomewhatindifferentmicrocomputer;inmostamechanismisprovidedtoatleastallowsomeflexibilityofchoosingwhichpinsareoutputsandwhichareinputs.Thismayapplytoallorsomeoftheports.SomeI/Olinesaresuitablefordirectinterfa
11、cingto,forexample,fluorescentdisplays,orcanprovidesufficientcurrenttomakeinterfacingothercomponentsstraightforward.SomedevicesallowanI/Oporttobeconfiguredasasystembustoallowoff-chipmemoryandI/Oexpansion.Thisfacilityispotentiallyusefulasaproductrangedevelops,sincesuccessiveenhancementsmaybecometoobig
12、foron-chipmemoryanditisundesirablenottobuildontheexistingsoftwarebase.Serialcommunicationwithterminaldevicesiscommonmeansofprovidingalinkusingasmallnumberoflines.Thissortofcommunicationcanalsobeexploitedforinterfacingspecialfunctionchipsorlinkingseveralmicrocomputerstogether.Boththecommonasynchronou
13、ssynchronouscommunicationschemesrequireprotocolsthatprovideframing(startandstop)information.ThiscanbeimplementedasahardwarefacilityorU(S)ART(Universal(synchronous)asynchronousreceiver/transmitter)relievingtheprocessor(andtheapplicationsprogrammer)ofthislow-level,time-consuming,detail.tismerelynecess
14、arytoselectedabaud-rateandpossiblyotheroptions(numberofstopbits,parity,etc.)andload(orreadfrom)theserialtransmitter(orreceiver)buffer.Serializationofthedataintheappropriateformatisthenhandledbythehardwarecircuit.TheDS18B20digitalthermometerprovides9-bitto12-bitCelsiustemperaturemeasurementsandhasana
15、larmfunctionwithnonvolatileuser-programmableupperandlowertriggerpoints.TheDS18B20communicatesovera1-Wirebusthatbydefinitionrequiresonlyonedataline(andground)forcommunicationwithacentralmicroprocessor.Ithasanoperatingtemperaturerangeof-55Cto+125Candisaccurateto0.5Covertherangeof-10Cto+85C.Inaddition,
16、theDS18B20canderivepowerdirectlyfromthedataline(“parasitepower”),eliminatingtheneedforanexternalpowersupply.EachDS18B20hasaunique64-bitserialcode,whichallowsmultipleDS18B20stofunctiononthesame1-Wirebus.Thus,itissimpletouseonemicroprocessortocontrolmanyDS18B20sdistributedoveralargearea.Applicationsth
17、atcanbenefitfromthisfeatureincludeHVACenvironmentalcontrols,temperaturemonitoringsystemsinsidebuildings,equipment,ormachinery,andprocessmonitoringandcontrolsystems.TheDS18B20canbepoweredbyanexternalsupplyontheVDDpin,oritcanoperatein“parasitepower”mode,whichallowstheDS18B20tofunctionwithoutalocalexte
18、rnalsupply.Parasitepowerisveryusefulforapplicationsthatrequireremotetemperaturesensingorthatareveryspaceconstrained.Figure1showstheDS18B20sparasite-powercontrolcircuitry,which“steals”powerfromthe1-WirebusviatheDQpinwhenthebusishigh.ThestolenchargepowerstheDS18B20whilethebusishigh,andsomeofthechargei
19、sstoredontheparasitepowercapacitor(CPP)toprovidepowerwhenthebusislow.WhentheDS18B20isusedinparasitepowermode,theVDDpinmustbeconnectedtoground.Inparasitepowermode,the1-WirebusandCPPcanprovidesufficientcurrenttotheDS18B20formostoperationsaslongasthespecifiedtimingandvoltagerequirementsaremet(seetheDCE
20、lectricalCharacteristicsandACElectricalCharacteristics).However,whentheDS18B20isperformingtemperatureconversionsorcopyingdatafromthescratchpadmemorytoEEPROM,theoperatingcurrentcanbeashighas1.5mA.Thiscurrentcancauseanunacceptablevoltagedropacrosstheweak1-Wirepullupresistorandismorecurrentthancanbesup
21、pliedbyCPP.ToassurethattheDS18B20hassufficientsupplycurrent,itisnecessarytoprovideastrongpulluponthe1-WirebuswhenevertemperatureconversionsaretakingplaceordataisbeingcopiedfromthescratchpadtoEEPROM.ThiscanbeaccomplishedbyusingaMOSFETtopullthebusdirectlytotherailasshowninFigure4.The1-Wirebusmustbeswi
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