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外文翻译

本科毕业设计（论文）外文翻译

学院电气工程与自动化学院

专业名称自动化

年级班级12-05

学生姓名于潇翔

指导老师朱艺锋

2016年6月8日

AT89C51In-CircuitProgramming

T.Islam,S.Ghosh,H.Saha

Thisapplicationnoteillustratesthein-circuitprogrammabilityoftheAtmelAT89C51Flash-basedmicrocontroller.Guidelinesfortheadditionofin-circuitprogrammabilitytoAT89C51applicationsarepresentedalongwithanapplicationexampleandthemodificationstoitrequiredtosupportin-circuitprogramming.AmethodisthenshownbywhichtheAT89C51microcontrollerintheapplicationcanbereprogrammedremotely,overacommercialtelephoneline.Thecircuitrydescribedinthisapplicationnotesupportsfivevoltprogrammingonly,requiringtheuseofanAT89C51-XX-5.ThestandardAT89C51requires12voltsforprogramming.ThesoftwareforthisapplicationmaybeobtainedbydownloadingfromAtmel’s

GeneralConsiderations

CircuitryaddedtosupportAT89C51incircuitprogrammingshouldappeartransparenttotheapplicationwhenprogrammingisnottakingplace.

EA/VPPmustbeheldhighduringprogramming.Inapplicationswhichdonotutilizeexternalprogrammemory,thispinmaybepermanentlystrappedtoVCC.Applicationsutilizingexternalprogrammemoryrequirethatthispinbeheldlowduringnormaloperation.

RSTmustbeheldactiveduringprogramming.Ameansmustbeprovidedforoverridingtheapplicationresetcircuit,whichtypicallyassertsRSTonlybrieflyafterpowerisapplied.

PSENmustbeheldlowduringprogramming,butmustnotbedrivenduringnormaloperation.

ALE/PROGispulsedlowduringprogramming,butmustnotbedrivenduringnormaloperation.

Duringprogramming,AT89C51I/Oportsareusedfortheapplicationofmodeselect,addressesanddata,possiblyrequiringthatthecontrollerbeisolatedfromtheapplicationcircuitry.Howthisisdoneisapplicationdependentandwillbeaddressedhereonlyingeneralterms.

PortUsedforInput

Duringprogramming,thecontrollermustbeisolatedfromsignalssourcedbytheapplicationcircuitry.Abufferwiththreestateoutputsmightbeinsertedbetweentheapplicationcircuitryandthecontroller,withthebufferoutputsthree-statedwhenprogrammingisenabled.Alternately,amultiplexermightbeusedtoselectbetweensignalsources,withsignalsappliedtothecontrollerbyeithertheapplicationcircuitryortheprogrammercircuitry.

PortUsedforOutput

Nocircuitchangesarerequirediftheapplicationcircuitrycantoleratethestatechangeswhichoccurattheportduringprogramming.Ifthepriorstateoftheapplicationcircuitrymustbemaintainedduringprogramming,alatchmightbeinsertedbetweenthecontrollerandtheapplicationcircuitry.Thelatchisenabledduringprogramming,preservingthestateoftheapplicationcircuitry.

AnApplicationExample

TheAT89C51applicationshowninFigure1isanimplementationofamovingdisplay.Thisapplicationwasselectedforitssimplicityandabilitytoshowgraphicallytheresultsofin-circuitreprogramming.Thetexttobedisplayedisprogrammedintothecontrolleraspartofitsfirmware,andcannotbechangedwithoutreprogrammingthedevice.

Thedisplayedtextispresentedinoneoftwomodesselectedbythefour-positionDIPswitch.Inthefirstmode,onecharacteratatimeentersthedisplayfromtherightandmovesquicklytotheleftthrougheachelementofthedisplaytoitsfinalpositionintheassembledmessage.Inthesecondmode,themessagemovesthroughthedisplay,fromrighttoleft,withthedisplayactingasawindowontothemessage.Thismodeisfamiliarasthemethodoftenusedindisplaysofstockprices.

TheoutputconsistsoffourDL1414T,four-digit,17-segmentalphanumericdisplayswithintegraldecodersanddrivers.Thisyields16totaldisplayelements,eachcapableofdisplayingdigits0-9,theuppercasealphabet,andsomepunctuationcharacters.ThedisplayablecharactercodesareASCII20H-5FH.

Apower-onresetcircuitanda6-MHzcrystaloscillatorcompletetheapplication.Neitherexternalprogrammemorynorexternaldatamemoryisused.

ModificationstotheApplicationtoSupport

In-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,whicheliminateserraticoperationofthedisplaysduetoprogrammeractivityonportszeroandtwo.Noisolationof

thedisplaydatainputsisrequired,sincedataappliedtotheinputsisignoredwhenthecontrolsignalsareinactive.

TheAT89C51resetcircuit,inputmultiplexerandoutputlatcharecontrolledbyasinglesignalgeneratedbytheprogrammer.Duringprogramming,resetisasserted,themultiplexerswitchesinputs,andthelatchfreezesthedisplaycontrollines.

Toensurethatthedisplaycontrollinesareinaknownstatebeforetheyarelatched,anAT89C51externalinterruptisusedtoallowtheprogrammertosignaltheapplicationbeforeassertingreset.Theapplicationfirmwarerespondstotheinterruptbydisplayingamessageanddeactivatingthedisplaycontrollines.

Afterprogramming,whenresetisdeasserted,thecontrollerportsarehighasthelatchbecomestransparent.Sincethedisplaycontrolinputsareinactivehigh,thedisplaycontentsarenotdisturbeduntilthenewprogramwritesthedisplay.Althoughnotessentialtothisapplication,itmightbeimperativeinsomeapplicationsthatthestateoftheperipheralcircuitrynotbedisturbedduringprogramming.

TheProgrammer

Theprogrammer（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.Ifrequiredforcompatibilitywithanapplication,programmersignalsmaybebufferedwiththree-statebufferssimilartothe74xx125.

TheAT89C51intheprogrammerdoesnotutilizeexternalprogramordatamemory,whichwouldrequiresacrificingneededI/Opins.ThisrequiresthatprogramcodeandI/Obuffersbekeptsmallenoughtofitinon-chipmemory.

RemoteProgrammingOveraCommercial

TelephoneLine

Theprogrammeranddisplayapplicationdescribedpreviouslyareconnectedtoaphonelineviaamodemataremotesite.Usingapersonalcomputerwithamodem,ausercanuploadanewprogramcontaininganewmessage,whichisprogrammedintotheAT89C51embeddedintheapplication.Whenprogrammingiscomplete,theapplicationexecutesthenewprogram,whichdisplaysthenewmessage.

LocalStation

ThelocalstationinthetestconfigurationconsistsofanIBMPCAT-classcomputerconnectedtoaHayes-compatible,Prometheus1200baudmodem.Themodemwasselectedbecauseitwasinexpensiveandavailable.Afastermodemmaybeusedifdesired,althoughoncethefiletransmissiontimeisreducedbelowoneminute,furtherreductionsintransmissiontimedonotfurtherreduceconnecttimecharges.Apossibleadvantagetohighertransmissionspeedsistheautomaticerrordetectionandcorrectionavailableinsomehighspeedmodems.

ProcommPlusversion2.01,acommercialdatacommunicationspackage,isusedtoconfigurethemodem,setupcommunicationsparameters,andestablishalinkwiththeremotemodem.ProcommPlusincludesamacrolanguagecalledASPECT,whichallowstheusertowriteandcompilescriptswhichimplementcustomfiletransferprotocols.AsimpleASPECTscriptwaswrittentoreadth