MCS51 In English.docx
- 文档编号:3705408
- 上传时间:2022-11-24
- 格式:DOCX
- 页数:24
- 大小:340.51KB
MCS51 In English.docx
《MCS51 In English.docx》由会员分享,可在线阅读,更多相关《MCS51 In English.docx(24页珍藏版)》请在冰豆网上搜索。
MCS51InEnglish
MCS-51Microcontroller
MaterialCollected&EditedBy:
ChuiHongWu
FujianAgriculturalandForestryUniversity
2008
TheFirstPart:
BasicKnowledgeofMicrocontroller
1.Introduction
Thischaptersetsthegroundworkforadetailedexplorationoftheinnerworkingsofasmallmicrocontroller.Wewillseethatthemicrocontrollerisoneofthemostbasicformsofcomputersystem.Althoughmuchsmallerthanitscousins—personalcomputersandmainframecomputers—microcontrollersarebuiltfromthesamebasicelements.Inthesimplestsense,computersproduceaspecificpatternofoutputsbasedoncurrentinputsandtheinstructionsinacomputerprogram.
WhatisaMicrocontroller?
Likemostcomputers,microcontrollersaresimplygeneral-purposeinstructionexecutors.Therealstarofacomputersystemisaprogramofinstructionsthatisprovidedbyahumanprogrammer.Thisprograminstructsthecomputertoperformlongsequencesofverysimpleactionstoaccomplishusefultasksasintendedbytheprogrammer.
OverallViewofaComputerSystem
Figure1providesahighlevelviewofacomputersystem.Bysimplychangingthetypesofinputandoutputdevices,thiscouldbeaviewofapersonalcomputer,aroom-sizedmainframecomputer,orasimplemicrocontroller(MCU).Theinputandoutput(I/O)devicesshowninthefigurehappentobetypicalI/Odevicesfoundinamicrocontrollercomputersystem.
Inputdevicessupplyinformationtothecomputersystemfromtheoutsideworld.Inapersonalcomputersystem,themostcommoninputdeviceisthetypewriter-stylekeyboard.Mainframecomputersusekeyboardsandpunchedcardreadersasinputdevices.Microcontrollercomputersystemsusuallyusemuchsimplerinputdevicessuchasindividualswitchesorsmallkeypads,althoughmuchmoreexoticinputdevicesarefoundinmanymicrocontroller-basedsystems.Anexampleofanexoticinputdeviceforamicrocontrolleristheoxygensensorinanautomobilethatmeasurestheefficiencyofcombustionbysamplingtheexhaustgases.
Mostmicrocontrollerinputscanonlyprocessdigitalinputsignalsatthesamevoltagelevelsasthemainlogicpowersource.The0-voltgroundleveliscalledVSSandthepositivepowersource(VDD)istypically5VDC(directcurrent).Alevelofapproximately0voltsindicatesalogic0signalandavoltageapproximatelyequaltothepositivepowersourceindicatesalogic1signal.
Ofcourse,therealworldisfullofanalogsignalsorsignalsthataresomeothervoltagelevel.SomeinputdevicestranslatesignalvoltagesfromsomeotherleveltotheVDDandVSSlevelsneededforthemicrocontroller.Otherinputdevicesconvertanalogsignalsintodigitalsignals(binaryvaluesmadeupof1sand0s)thatthecomputercanunderstandandmanipulate.Somemicrocontrollersevenincludesuchanalog-to-digitalconvertercircuitsonthesameintegratedcircuit.
Transducerscanbeusedtotranslateotherreal-worldsignalsintologiclevelsignalsthatamicrocontrollercanunderstandandmanipulate.Someexamplesincludetemperaturetransducers,pressuresensors,lightleveldetectors,andsoforth.Withsuchtransducers,almostanyphysicalpropertycanbeusedasaninputtoacomputersystem.
ComputerSystemOutputs
Outputdevicesareusedtocommunicateinformationoractionsfromthecomputersystemtotheoutsideworld.Inapersonalcomputersystem,themostcommonoutputdeviceistheCRT(cathoderaytube)display.Microcontrollersystemsoftenusemuchsimpleroutputdevicessuchasindividualindicatorlampsorbeepers.
Translationcircuits(sometimesbuiltintothesameintegratedcircuitasthemicrocomputer)canconvertdigitalsignalsintoanalogvoltagelevels.Ifnecessary,othercircuitscantranslateVDDandVSSlevelsthatarenativetoanMCUintoothervoltagelevels.
The“controller”inmicrocontrollercomesfromthefactthatthesesmallcomputersystemsusuallycontrolsomethingascomparedtoapersonalcomputerthatusuallyprocessesinformation.Inthecaseofthepersonalcomputer,mostoutputisinformation(eitherdisplayedonaCRTscreenorprintedonpaper).Incontrast,inamicrocontrollersystem,mostoutputsarelogicleveldigitalsignalsthatareusedtodrivedisplayLEDs(light-emittingdiodes)orelectricaldevicessuchasrelaysormotors.
CentralProcessorUnit(CPU)
TheCPUisatthecenterofeverycomputersystem.ThejoboftheCPUistoobedientlyexecutetheprogramofinstructionsthatwassuppliedbytheprogrammer.AcomputerprograminstructstheCPUtoreadinformationfrominputs,toreadinformationfromandwriteinformationto
workingmemory,andtowriteinformationtooutputs.Someprograminstructionsinvolvesimpledecisionsthatcausetheprogramtoeithercontinuewiththenextinstructionortoskiptoanewplaceintheprogram.Inalaterchapter,wewilllookcloselyatthesetofavailableinstructionsforaparticularmicrocontroller.
Inmainframeandpersonalcomputers,thereareactuallayersofprograms,startingwithinternalprograms,thatcontrolthemostbasicoperationsofthecomputer.Anotherlayerincludesuserprogramsthatareloadedintothecomputersystemmemorywhentheyareabouttobeused.Thisstructureisverycomplexandwouldnotbeagoodexampleforshowingabeginnerhowacomputerworks.
Inamicrocontroller,usuallyonlyoneprogramisatworkinaparticularcontrolapplication.Forexample,theMCS-51CPUrecognizesonlyabout111differentinstructions,butthesearerepresentativeoftheinstructionsetsofanycomputersystem.ThiskindofcomputersystemisagoodmodelforlearningthebasicsofcomputeroperationbecauseitispossibletoknowexactlywhatishappeningateverytinystepastheCPUexecutesaprogram.
Clock
Withveryfewexceptions,computersuseasmallclockoscillatortotriggertheCPUtomovefromonestepinasequencetothenext.Inthechapteroncomputerarchitecture,wewillseethateventhesimpleinstructionsofamicrocontrollerarebrokendownintoaseriesofevenmorebasicsteps.EachofthesetinystepsintheoperationofthecomputertakesonecycleoftheCPUclock.
ComputerMemory
Severalkindsofcomputermemoryareusedforvariouspurposesincomputersystems.Themainkindsofmemoryfoundinmicrocontrollersystemsare:
.Read-onlymemory(ROM)
.Randomaccessread/writememory(RAM)
ROMisusedmainlyforprogramsandpermanentdatathatmustremainunchangedevenwhenthereisnopowerappliedtothemicrocontroller.
RAMisusedfortemporarystorageofdataandintermediatecalculationresultsduringoperation.
WhatisaMicrocontroller?
Somemicrocontrollersincludeotherkindsofmemory,suchas:
.
Erasableprogrammableread-onlymemory(EPROM).Electricallyerasableprogrammableread-onlymemory(EEPROM).Wewilllearnmoreaboutthesekindsofmemoryinalaterchapter.
Thesmallestunitofcomputermemoryisasinglebitthatcanstoreonevalueof0or1.Thesebitsaregroupedintosetsofeightbitstomakeonebyte.Largercomputersfurthergroupbitsintosetsof16or32tomakeaunitcalledaword.Thesizeofawordcanbedifferentfordifferentcomputers,butabyteisalwayseightbits.
Personalcomputersworkwithverylargeprogramsandlargeamountsofdata,sotheyusespecialformsofmemorycalledmassstoragedevices.Floppydisks,harddisks,andcompactdiscsarememorydevicesofthistype.ItisnotunusualtofindseveralmillionbytesofRAMmemoryinapersonalcomputer.Eventhisisnotenoughtoholdthelargeprogramsanddatausedbypersonalcomputers,somostpersonalcomputersalsoincludeaharddiskwithtensorevenhundredsofmillionsorevenbillionsofbytesofstoragecapacity.Compactdiscs,verysimilartothoseusedforpopularmusicrecordings,haveacapacityofabout600millionbytesofread-onlymemory.Incomparison,thesmallmicrocontrollersystemswearediscussinginthisbooktypicallyhaveatotalof1,000to64,000bytesofmemory.
ComputerProgram
Figure1showstheprogramasacloudbecauseitoriginatesintheimaginationofacomputerprogrammerorengineer.Thisiscomparabletoanelectricalengineerthinkingupanewcircuitoramechanicalengineerfiguringoutanewassembly.ThecomponentsofaprogramareinstructionsfromtheinstructionsetoftheCPU.JustasacircuitdesignercanbuildanaddercircuitoutofsimpleAND,OR,andNOTelements,aprogrammercanwriteaprogramtoaddnumberstogetheroutofsimpleinstructions.
ProgramsarestoredinthememoryofacomputersystemwheretheycanbesequentiallyexecutedbytheCPU.Inthechapteronprogramming,wewilllearnhowtowriteprogramsandpreparethemforloadingintothememoryofacomputer.
TheMicrocontroller
Nowthatwehavediscussedthevariouspartsofacomputersystem,wearereadytotalkaboutjustwhatamicrocontrolleris.ThetophalfofFigure2showsagenericcomputersystemwithaportionenclosedinadashedoutline.Thisoutlinedportionisamicrocontrollerandthelowerhalfofthefigureisablockdiagramshowingitsinternalstructureingreaterdetail.Thecrystalisnotcontainedwithinthemicrocontroller,butitisarequiredpartoftheoscillatorcircuit.Insomecases,alessexpensivecomponentsuchasaceramicresonatororaresistor-capacitor(R-C)circuitmaybeusedinsteadofthiscrystal.
AmicrocontrollercanbedefinedasacompletecomputersystemincludingaCPU,memory,aclockoscillator,andI/Oonasingleintegratedcircuitchip.WhensomeoftheseelementssuchastheI/Oormemoryaremissing,theintegratedcircuitwouldbecalledamicroprocessor.TheCPUinapersonalcomputerisamicroprocessor.TheCPUinamainframecomputerismadeupofmanyintegra
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- MCS51 In English