文献翻译——51单片机在编程电路中的应用

第1页外文文献资料AT89C51In-CircuitProgrammingThisapplicationnoteillustratesthein-circuitprogrammabilityoftheAtmelAT89C51Flash-basedmicrocontroller.Guidelinesfortheadditionofin-circuitprogrammabilitytoAT89C51applicationsarepresentedalongwithanapplicationexampleandthemodificationstoitrequiredtosupportin-circuitprogramming.AmethodisthenshownbywhichtheAT89C51microcontrollerintheapplicationcanbereprogrammedremotely,overacommercialtelephoneline.Thecircuitrydescribedinthisapplicationnotesupportsfivevoltprogrammingonly,requiringtheuseofanAT89C51-XX-5.ThestandardAT89C51requires12voltsforprogramming.ThesoftwareforthisapplicationmaybeobtainedbydownloadingfromAtmelsGeneralConsiderationsCircuitryaddedtosupportAT89C51incircuitprogrammingshouldappeartransparenttotheapplicationwhenprogrammingisnottakingplace.EA/VPPmustbeheldhighduringprogramming.Inapplicationswhichdonotutilizeexternalprogrammemory,thispinmaybepermanentlystrappedtoVCC.Applicationsutilizingexternalprogrammemoryrequirethatthispinbeheldlowduringnormaloperation.RSTmustbeheldactiveduringprogramming.Ameansmustbeprovidedforoverridingtheapplicationresetcircuit,whichtypicallyassertsRSTonlybrieflyafterpowerisapplied.PSENmustbeheldlowduringprogramming,butmustnotbedrivenduringnormaloperation.ALE/PROGispulsedlowduringprogramming,butmustnotbedrivenduringnormaloperation.Duringprogramming,AT89C51I/Oportsareusedfortheapplicationofmodeselect,addressesanddata,possiblyrequiringthatthecontrollerbeisolatedfromtheapplicationcircuitry.Howthisisdoneisapplication第2页dependentandwillbeaddressedhereonlyingeneralterms.PortUsedforInputDuringprogramming,thecontrollermustbeisolatedfromsignalssourcedbytheapplicationcircuitry.Abufferwiththreestateoutputsmightbeinsertedbetweentheapplicationcircuitryandthecontroller,withthebufferoutputsthree-statedwhenprogrammingisenabled.Alternately,amultiplexermightbeusedtoselectbetweensignalsources,withsignalsappliedtothecontrollerbyeithertheapplicationcircuitryortheprogrammercircuitry.PortUsedforOutputNocircuitchangesarerequirediftheapplicationcircuitrycantoleratethestatechangeswhichoccurattheportduringprogramming.Ifthepriorstateoftheapplicationcircuitrymustbemaintainedduringprogramming,alatchmightbeinsertedbetweenthecontrollerandtheapplicationcircuitry.Thelatchisenabledduringprogramming,preservingthestateoftheapplicationcircuitry.AnApplicationExampleTheAT89C51applicationshowninFigure1isanimplementationofamovingdisplay.Thisapplicationwasselectedforitssimplicityandabilitytoshowgraphicallytheresultsofin-circuitreprogramming.Thetexttobedisplayedisprogrammedintothecontrolleraspartofitsfirmware,andcannotbechangedwithoutreprogrammingthedevice.Thedisplayedtextispresentedinoneoftwomodesselectedbythefour-positionDIPswitch.Inthefirstmode,onecharacteratatimeentersthedisplayfromtherightandmovesquicklytotheleftthrougheachelementofthedisplaytoitsfinalpositionintheassembledmessage.Inthesecondmode,themessagemovesthroughthedisplay,fromrighttoleft,withthedisplayactingasawindowontothemessage.Thismodeisfamiliarasthemethodoftenusedindisplaysofstockprices.TheoutputconsistsoffourDL1414T,four-digit,17-segmentalphanumericdisplayswithintegraldecodersanddrivers.Thisyields16totaldisplayelements,eachcapableofdisplayingdigits0-9,theuppercasealphabet,andsomepunctuationcharacters.ThedisplayablecharactercodesareASCII20H-第3页5FH.Apower-onresetcircuitanda6-MHzcrystaloscillatorcompletetheapplication.Neitherexternalprogrammemorynorexternaldatamemoryisused.ModificationstotheApplicationtoSupportIn-CircuitProgrammingFigure2showstheapplicationmodifiedforin-circuitprogramming.Itisassumedthattheprogrammer,wheninactive,willneitherdrivenorexcessivelyloadtheapplication.Sincetheapplicationdoesnotuseexternalprogrammemory,EA/VPPonthecontrollerisconnectedtoVCC.Thismeetstherequirementforprogramming.Theresetcircuithasbeenmodifiedbytheadditionoftwotransistors,whichallowRSTonthecontrollertobeforcedhighbytheprogrammer.PSENandALE/PROG,unusedinthebasicapplication,areunderthedirectcontroloftheprogrammer.ProgrammingrequiresprogrammeraccesstoallofthefourAT89C51I/Oports,asdocumentedinthedatasheet.Theprogrammerisconnecteddirectlytothosecontrollerpinswhichareunusedbytheapplication,whileaccesstopinsusedbytheapplicationrequiresspecialtreatment,asexplainedinthefollowingparagraphs.TheleastsignificantfourbitsoftheaddressgeneratedbytheprogrammeraremultiplexedontoportoneofthecontrollerwiththedatafromtheDIPswitch.Notethatthefourresistorsaddedattheswitcharenotrequiredinthebasicapplication,sincetheAT89C51providesinternalpull-upsonportone.Duringthenormaloperationoftheapplication,controllerportszeroandtwoprovidedataandcontrolsignals(respectively)tothedisplays.Duringprogrammingandprogramverification,theprogrammerassertscontrolofportzeroandpartofporttwo.Theprogrammerisconnectedtoportszeroandtwowithoutbuffering,since,wheninactive,itspresencedoesnotaffectthenormaloperationoftheapplication.Atransparentlatchhasbeenaddedbetweenporttwoofthecontrollerandthedisplaycontrolinputs.Thelatchholdsthedisplaycontrolsignalsinactiveduringprogramming,whicheliminateserraticoperationofthe第4页displaysduetoprogrammeractivityonportszeroandtwo.Noisolationofthedisplaydatainputsisrequired,sincedataappliedtotheinputsisignoredwhenthecontrolsignalsareinactive.TheAT89C51resetcircuit,inputmultiplexerandoutputlatcharecontrolledbyasinglesignalgeneratedbytheprogrammer.Duringprogramming,resetisasserted,themultiplexerswitchesinputs,andthelatchfreezesthedisplaycontrollines.Toensurethatthedisplaycontrollinesareinaknownstatebeforetheyarelatched,anAT89C51externalinterruptisusedtoallowtheprogrammertosignaltheapplicationbeforeassertingreset.Theapplicationfirmwarerespondstotheinterruptbydisplayingamessageanddeactivatingthedisplaycontrollines.Afterprogramming,whenresetisdeasserted,thecontrollerportsarehighasthelatchbecomestransparent.Sincethedisplaycontrolinputsareinactivehigh,thedisplaycontentsarenotdisturbeduntilthenewprogramwritesthedisplay.Althoughnotessentialtothisapplication,itmightbeimperativeinsomeapplicationsthatthestateoftheperipheralcircuitrynotbedisturbedduringprogramming.TheProgrammerTheprogrammer(Figure3)generatestheaddresses,dataandcontrolsignalsnecessarytoprogramtheAT89C51embeddedintheapplication.TheprogrammercircuitryconsistsofanAT89C51andanRS-232leveltranslator.Thecontrollerrunsat11.0592MHz,whichallowstheserialporttooperateatanumberofstandardbaudrates.AMaximMAX232linedriver/receiverproducesRS-232levelsattheserialinterfacewhilerequiringonlyafivevoltsupply.Manyofthesignalsgeneratedbytheprogrammerareconnecteddirectly,withoutbuffering,totheAT89C51intheapplication.Thesesignals,wheninactive,arenotthreestated,butarepulledhigh.TheAT89C51hasinternalpull-upsofapproximatelythreeKohmsonportsone,twoandthree.Becauseportzerodoesnothaveinternalpull-ups,externalpull-upsoftenKohmshavebeenaddedtopermitproperoperationofprogramverificationmode.Thesampleapplicationoperatescorrectlyinthisenvironment.Ifrequiredfor第5页compatibilitywithanapplication,programmersignalsmaybebufferedwiththree-statebufferssimilartothe74xx125.TheAT89C51intheprogrammerdoesnotutilizeexternalprogramordatamemory,whichwouldrequiresacrificingneededI/Opins.ThisrequiresthatprogramcodeandI/Obuffersbekeptsmallenoughtofitinon-chipmemory.RemoteProgrammingOveraCommercialTelephoneLineTheprogrammeranddisplayapplicationdescribedpreviouslyareconnectedtoaphonelineviaamodemataremotesite.Usingapersonalcomputerwithamodem,ausercanuploadanewprogramcontaininganewmessage,whichisprogrammedintotheAT89C51embeddedintheapplication.Whenprogrammingiscomplete,theapplicationexecutesthenewprogram,whichdisplaysthenewmessage.LocalStationThelocalstationinthetestconfigurationconsistsofanIBMPCAT-classcomputerconnectedtoaHayes-compatible,Prometheus1200baudmodem.Themodemwasselectedbecauseitwasinexpensiveandavailable.Afastermodemmaybeusedifdesired,althoughoncethefiletransmissiontimeisreducedbelowoneminute,furtherreductionsintransmissiontimedonotfurtherreduceconnecttimecharges.Apossibleadvantagetohighertransmissionspeedsistheautomaticerrordetectionandcorrectionavailableinsomehighspeedmodems.ProcommPlusversion2.01,acommercialdatacommunicationspackage,isusedtoconfigurethemodem,setupcommunicationsparameters,andestablishalinkwiththeremotemodem.ProcommPlusincludesamacrolanguagecalledASPECT,whichallowstheusertowriteandcompilescriptswhichimplementcustomfiletransferprotocols.AsimpleASPECTscriptwaswrittentoreadthecontentsofaprogramfileanduploadittotheremoteprogrammer.Thefiletransferprotocol(FTP)implementedisasimplesend-and-wait,packet-orientedprotocol.ThetransmitandreceivemodesoftheFTPareillustratedbytheflowchartsinfigures4and5,respectively.Thetransmittersendseachpacketwithoutflowcontrolandwaitsforaresponse.Theprogrammer(thereceiver)readsanddissectsthepacketwhilecalculating第6页achecksum.Ifthecalculatedchecksumisvalid,theprogrammeracknowledgesthepacketbysendinganACK.Ifthechecksumisinerror,theprogrammernegativelyacknowledgesthepacketbysendingaNAK.UponreceiptofanACK,thetransmittersendsthenextpacket.IfthetransmitterreceivesaNAK,itresendsthesamepacket.Transmissionproceedsinthismanneruntiltheentirefilehasbeentransferred.TheprogrammermightrespondtoapacketbysendingaCAN,whichindicatesthatanon-recoverableerrorhasoccurredandthatthetransmittershouldimmediatelyabortthefiletransfer.Iftheprogrammerfailstorespondtoapacketwithinalimitedperiodoftime,thetransmitterwillresendthesamepacket.Thetransmitterwillcontinuetoresendthesamepacketuntilavalidresponseisreceivedoruntiltheallowednumberofattemptsisexceeded,atwhichtimethefiletransferisaborted.Aftereachpacketisreceivedandvalidatedbytheprogrammer,thedatacontainedinthepacketisprogrammedintotheAT89C51controllerintheapplication.Afterprogramming,thedataisreadbackfromthecontrollerandverifiedagainstthereceivedpacketdata.Successfulverificationindicatessuccessfulprogramming,causingtheprogrammertosendACKtothetransmitter.Ifprogrammingfails,theprogrammersendsCANtosignalthetransmittertoabortthefiletransfer.ThesimplicityoftheFTPreducestheamountofAT89C51programmemoryusedintheprogrammer.Thesend-andwaitnatureoftheFTPallowsinter-packetdelaysduetoAT89C51programanderasetimestobeeasilyabsorbed.Supportforprogramverificationistransparent,requiringnoexplicitcommandorresultcodes,oradditionaldatatransfers.ThefileswhichareuploadedtotheprogrammerarecreatedwiththetoolsintheIntelMCS-51SoftwareDevelopmentPackagefortheIBMPC.IncludedinthepackagearetheMCS-51MacroAssembler,MCS-51RelocatorandLinker,andausefulutility,OH.OHconvertsanabsolute8051objectfiletoanequivalentASCIIhexadecimalobjectfile.TherecordsinthehexfileproducedbytheOHutilityserve,unchanged,asthepacketsintheFTPdescribedabove;noservicefieldsneedtobeadded.Thecolonwhichbeginseachrecordservesasthepacketsignaturefield.The第7页loadaddressfieldservesasthepacketsequencenumber.Achecksumisprovidedasthelastfieldineachrecord.Sinceseven-bitASCIIcodingisutilized,theeighthbitofeachbyteisavailabletobeusedforparitychecking.BecausetheAT89C51intheprogrammerdoesnotutilizeexternaldatamemory,necessarypacketbufferingmustbedoneusinginternalRAM.LimitedmemoryprecludestheuseofconventionalFTPswhichutilizepacketsof128bytesandlarger.Thehexpacketformatusedinthisapplicationlimitspacketdatafieldsto16orfewerentries,requiringlittlememoryforbuffering.Thereadyavailabilityofautilityforcreatingthepacketizedprogramfile,combinedwithsmallpacketsizeandadequateerrorchecking,makesthehexpacketformatanearidealsolutionforthisapplication.AdisadvantageistheuseofASCII,whichrequireseachprogramdatabytetobeexpressedastwohexcharacters.Thisdemandsthatnearlytwiceasmanybytesbetransferredasmightotherwiseberequired.Thisisnotaseverelimitation,however,sincetypicalfiletransfertimesarelessthanoneminute.Overall,thesimplicityofthecustomFTP/hexpacketformatimplementationoutweighsthedrawbacks.RemoteStationTheremotestationinthetestconfigurationconsistsofthedisplayapplicationandprogrammercircuits,describedpreviously,connectedtoaHayes-compatible,Prometheus1200baudmodem.Duringnormaloperation,theapplicationexecutesitsinternalprogramwhilethemodemandprogrammermonitorthephonelineforincomingcalls.Afteracallhasbeendetectedandaconnectionestablished,theprogrammerforcestheapplicationtosuspendexecutionofitsprogram.ThenewprogramisthendownloadedandprogrammedintotheAT89C51embeddedintheapplication.Whenprogrammingiscomplete,theapplicationisallowedtobeginexecutionofitsnewprogram,andtheprogrammerreturnstomonitoringthephonelineforthenextcall.Theprogrammerpowersupwithitsprogrammingcontroloutputsinactive,allowingtheapplicationtorunnormally.Afterconfiguringthemodemto第8页answerincomingcalls,theprogrammerputsitselftosleep.Theprogrammerwillnotdisturbtheapplicationuntilanewprogramistobedownloaded.TheprogrammercontrolsthemodembysendingASCIIcommandstringsovertheserialinterface,towhichthemodemrespondswithHayes-styleASCIInumericcodes.ThesoftwareisdesignedforusewithHayes-compatiblemodems,whichincludesthePrometheusProModem1200usedhere.Theserialinterface,throughwhichtheprogrammerconnectstothemodem,supportstwohandshakingsignals,DTRandDSR.Onpowerup,theprogrammerassertsDTR,towhichthemodemrespondsbyassertingDSR.Ifthemodemshouldfailtorespondtoanycommand,includingthecommandtohangup,theprogrammerdeassertsDTR,whichforcesthemodemtodroptheline.Themodemmonitorsthephonelinewhiletheprogrammersleeps,waitingforanincomingcall.Whenacallisdetected,themodemanswersandattemptstoestablishcommunicationwiththecaller.Ifaconnectionisestablished,themodemsendsacodetotheprogrammer,wakingitup.Theprogrammerverifiestheconnectcodeandbeginspollingforavalidpacketheader.Incomingpacketsmustarrivefewerthanthirtysecondsapart,orthemodemdropstheline(hangsup)andtheprogrammerreturnstosleep,waitingforthenextcall.Ifthecallerhangsup,thethirtysecondperiodmustexpirebeforeanothercallwillbeanswered.Callsincomingduringtheresetdelayperiodareignored.Ifavalidpacketheaderisreceivedpriortotheexpirationoftheresetdelayperiod,theprogrammerwillattempttoreadandvalidatetheincomingpacket.Atanytimeduringpacketreception,aninvalidcharacter,parityerrorortimeoutduringcharacterreceptionwillcausethepartialpackettobedeclaredinvalidanddiscarded.Twopackettypesaredefined:dataandend-of-file.Adatapacketcontainsfivefieldsinadditiontothepacketheader,oneofwhichisavariablelengthdatafield.ThedatafieldcontainsprogramdatatobewrittenintotheAT89C51controllerintheapplication.Theloadaddressfieldcontainstheaddressatwhichthedataistobewritten.Theend-of-filepacketcontainsthesamefieldsasthedatapacket,exceptthatthedatafieldisempty.Thispackettypehasspecialmeaningtotheprogrammer,as第9页explainedbelow.Anypacketwhichcontainsaninvalidrecordtype,recordlengthorchecksumisinvalid.Programdataaccumulatedduringtheprocessingofaninvalidpacketisdiscarded.TheprogrammersendsaNAKtothetransmittertosignalreceptionofaninvalidpacketandresumespollingforavalidpacketheader.Receiptofthefirstvaliddatapacketcausestheprogrammertointerrupttheapplicationcontroller.Thecontrollerrespondstotheinterruptbyabandoningexecutionofitsusualprogramanddisplayingamessageindicatingthatprogrammingistakingplace.Ifthisisthefirstvaliddatapacketsincepowerwasappliedoranend-of-filepacketwasreceived,theprogrammerassertsthecontrolsignalsnecessarytoerasetheprogrammemoryintheapplicationcontroller.Theprogrammerthenplacesthecontrollerinprogrammingmode.Thefirstandsubsequentvaliddatapacketsaredissectedastheyarereceivedandthedatawhichtheycontainisprogrammedintotheapplicationcontrollerattheaddressindicatedinthepacketloadaddressfield.Afterprogramming,thedataisreadbackfromthecontrollerandverifiedagainstthereceivedpacketdata.Successfulverificationindicatesthatprogrammingwassuccessful,causingtheprogrammertosendACKtothetransmitter.Theprogrammerthenresumespollingforavalidpacketheader,subjecttothethirtysecondresetdelay.Ifprogrammingfails,theprogrammersendsCANtosignalthetransmittertoabortthefiletransfer.Themodemdropsthelineandtheprogrammerreturnstosleep,waitingforthenextcall.Theapplicationcontrollerisleftinprogrammingmode,preventingitfromexecutingtheincompleteorinvalidprogramwhichitcontains.ItisimportanttonotethatinvalidpacketsareNEVERprogrammedintotheapplicationcontroller.Todosowouldrequirethattheprogrammemoryinthecontrollerbecompletelyerasedbeforetheerrorcouldbecorrected,causingthenon-recoverablelossofallpreviousprogramdata.Uponreceiptofanend-of-filepacket,theprogrammerreturnsitscontroloutputstotheinactive,poweronstate,allowingtheapplicationcontroller第10页tobeginexecutionofthenewprogram.Theprogrammerthenresumespollingforavalidpacketheader,subjecttothethirtysecondresetdelay.Ifavalidpacketisreceivedpriortotheexpirationofthethirtyseconddelay,anotherprogrammingcyclebegins,whichcanonlybeterminatedbythereceptionofavalidend-of-filepacket.Iftheresetdelayexpirespriortothereceptionofavalidend-of-filepacket,themodemwilldropthelineandtheprogrammerwillreturntosleep,waitingforthenextcall.Inthiscase,theapplicationcontrollerisleftinprogrammingmode,preventingitfromexecutingitsprogram.Toreturntheapplicationtonormaloperation,anothercallmustbereceived,andavalidprogramfileuploaded,terminatedbyanend-of-filepacket.第11页中文翻译稿51单片机在编程电路中的应用本应用指南说明了AtmelAT89C51是可在线可编程的微控制器。它为电路编程提出了相应的例子，程序的修改需要在线编程的支持。这类显示方法在应用程序中的AT89C51单片机可通过电话线远程控制。该应用指南所描述的电路只支持5v电压下编程。此应用软件可以到Atmel进行下载。总论当不在进行程序设计的时候，在电路设计中的AT89C51设计将变得透明化。在编程期间必须重视EA/VPP这一脚。在不使用外部程序存储器的应用程序中，这脚可能会永久接到VCC。应用程序使用的外部程序存储器要求这一脚为低电平才能正常运行。RST在编程期间必须为高电平。应该提供一种方法使得电路通入电源以后，使RST代替主要的复位电路起到复位的作用。在编程过程中，PSEN必须保持低电平，在正常运行期间绝不能使用。ALE/PROG在编程过程中输出低电平，在正常运行期间绝不能使用。在编程过程中，AT89C51的I/O端口是用于模式应用程序，地址和数据选择的，可能需要该控制器从应用的电路隔离。如何做到这一点取决于应用程序。输入端口在编程过程中，控制器必须与应用电路的信号来源隔离。带有三个输出状态的缓冲区会在应用程序之间插入电路和控制器，同时在编程时缓冲区输出三种状态。一个多路复用器可用于信号源之间进行选择，适用于任何一方的应用电路或编程控制器电路的信号。输出端口如果应用的电路可以允许端口在编程过程中的状态变化，则不需要改变电路。如果应用电路的状态，必须事先在编程过程中的保持不变，可能在控制器和应用电路中插入锁存。锁存在编程期间是可用的，并保存应用程序的电路状态。应用实例应用是该AT89C51一个移动的显示情况。此应用程序有在电路重新编程时将结果以图表的形式显示的简单能力。文本显示被设计作为其硬件的一部分，不能在无改编情况第12页下变化。显示的文本可在4位DIP开关选择两种模式之一中进行。在第一种模式的时候，进入一个字符从右边显示和快速移动，通过每个元素显示其在最后的装配位置的左侧。在第二个模式，信息在信息窗口中右到左移动显示。这种模式与常常在股票价格的显示器所使用的方法类似。输出包括四个DL1414T，4位17段的积分解码器和驱动程序的字母数字显示器。这就产生了16名显示元素，每个数字有0-9的显示能力，是大写字母，标点符号和一些字符。可显示字符的ASCII码，范围为20H-5FH。上电复位电路和一个6MHz的晶体振荡器完成应用软件程序。无论外部程序存储器或外部数据存储器都时可用的。支持应用程序的修改据推测，编程器在休眠时，既不会驱动，也不会加载应用程序。由于