电气自动化专业英文翻译2设计论文.docx
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电气自动化专业英文翻译2设计论文.docx
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电气自动化专业英文翻译2设计论文
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Computercontroltechnology
1Computerstructureandfunction
Thissectionintroducestheinternalarchitectureofacomputeranddescribesexecutioncycleisbrokendownintoitsvariouscomponents.
Atthemostbasiclevel,acomputersimplyexecutesbinary-codedresults.Forageneral-purposeprogrammablecomputer,fournecessaryelementsarethememory,centralprocessingunit(CPU,orsimplyprocessor),anexternalprocessorbus,andaninputoutputsystemasindicatedinFig.3-1A-1.
Fig.3-1A-1Basicelementsofacomputer
Thememorystoresinstructionsanddata.
TheCPUreadsandinterpretstheinstructions,readsthedatarequiredbyeachinstruction,executestheactionrequiredbytheinstruction,andstorestheresultsbackinmemory.OneoftheactionsthatisrequiredoftheCPUistoreaddatafromorwritedatatoanexternaldevice.Thisiscarriedoutusingtheinputoutputsystem.
Theexternalprocessorbusisasetofelectricconductorsthatcarriesdata,addressandcontrolinformationbetweentheothercomputerelements.
1-1Thememory
Inordertousethecontentsofmemory,theprocessormustfetchthecontentsoftherightlocation.Tocarryoutafetch,theprocessorplaces(enables)thebinary-codedaddressofthedesiredlocationontotheaddresslinesoftheexternalprocessorbus.Thememorythenallowsthecontentsoftheaddressedmemorylocationtobereadbytheprocessor.Theprocessoffetchingthecontentsofamemorylocationdoesnotalterthecontentsofthatlocation.
InstructionsinmemoryInstructionsstoredinmemoryarefetchedbytheCPUandunlessprogrambranchesoccur,theyareexecutedinthesequencetheyappearinmemory.Aninstructionwrittenasabinarypatterniscalledamachine-languageinstruction.OnewaytoachievemeaningfulpatternsistodivideupthebitsintofieldsasindicatedinFig.3-1A-2,witheachfieldcontainingacodeforadifferenttypeofinformation.
Fig.3-1A-2Arrangementofprogramanddatainmemory
Eachinstructioninoursimplecomputercanbedividedupintofourfieldsof4bitseach.Eachinstructioncancontainoperationcode(oropcode,eachinstructionarealinstructionsettherearemanymoreinstructions.Thereisalsoamuchlargenumberofmemorylocationsinwhichtostoreinstructionsanddata.Inordertoincreasethenumberofmemorylocations,theaddressfieldsand16bitsifweusethesameapproach.Thereareanumberofwaystoincreasetheaddressingrangeofthemicroprocessorwithoutincreasingtheinstructionlength:
variableinstructionfield,multiwordinstructions,multipleaddressingmodes,variableinstructionlength.Wewillnotdiscussthemindetail.
Datainmemorydataisinformationthatisrepresentedinmemoryasacode.Forefficientuseofthememoryspaceandprocessingtime,mostcomputersprovidethecapabilityofmanipulatingdataofdifferentlengthsandrepresentationsinmemory.Thevariousdifferentrepresentationsrecognizedbytheprocessorarecalleditsdatatypes.Thedatatypesnormallyusedare:
bit,binary-codeddecimaldigit(4-bitnibble,BCD),byte(8bits),word(2bytes),doubleword(4bytes).
Someprocessorsprovideinstructionsthatmanipulateotherdatatypessuchassingle-precisionfloating-pointdatatypes(32bits)anddouble-precisionfloating-pointdatatypes(64bits).Thereisanothertypeofdata—characterdata.Itisalsousuallyrepresentedin8bits.Eachcomputerterminalkeyandkeycombination(suchasshiftandcontrolfunctions)onastandardterminalkeyboardStandardCodeforInformationInterchange(ASCII).
TypeofmemoryIntheapplicationsofdigitalcontrolsystem,wealsoconcernedwiththecharacteristicsofdifferentmemorytechniques.Forprimarymemory,weneedittobestoredinformationtemporarilyandtobewrittenandgotinformationfromsuccessiveorfromwidelydifferentlocations.Thistypememoryiscalledrandom-accessmemory(RAM).Insomecasewedonotwanttheinformationinmemorytobelost.Sowearewillingtousespecialtechniquestowriteintomemory.Ifwritingisaccomplishedonlyoncebyphysicallychangingconnections,thememoryiscalledaread-onlymemory(ROM).Iftheinterconnectionpatterncanbeprogrammedtobeset,thememoryiscalledaprogrammableread-onlymemory(PROM).Ifrewritingcanbeaccomplishedwhenitisnecessary,weerasableprogrammableread-onlymemory(EPROM).AnelectronicallyerasablePROMisabbreviatedEEPROM.
1-2TheCPU
TheCPU’sjobistofetchinstructionsfrommemoryandexecutetheseinstructions.ThestructureoftheCPUisshowninFig.3-1A-3.Itcomponents:
anarithmeticandlogicalunit(ALU),asetofregisters,aninternalprocessorbusandcontroller.
Fig.3-1A-3Centralprocessingunit(CPU)
TheseandothercomponentsoftheCPUandtheirparticipationinth
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