广东高考英语试题及答案.docx
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广东高考英语试题及答案.docx
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广东高考英语试题及答案
英文资料及中文翻译
OneAbriefintroductionofDDSsystem
1thebasicprincipleofDDS
ThebasicprincipleistouseDDSsamplingtheorem,throughthequeryingmethodproducewaveform.ThestructureofDDShasalotofkinds,thebasicofthecircuitprincipleavailablefigure1-1tosaid.
K
Fs
FO
Figure1-1DDSschematic
PhaseaccumulatorsbyNaadderandNaaccumulateregisterscascadecomposition.Eachtoaclockpulsefs,adderwillfrequencycontrolwordkandaccumulateregisterstheaccumulationphaseoutputdatatogetherandaddtheresultsofdatasenttoaccumulateregisterinput.Accumulateregistersadderwilllastclockpulsethatisproducedwhenthenewroleofthephasetotheadderfeedbackdatainput,sothattheaddernextclockpulseundertheeffectoffrequencycontrolwordtocontinuewithaddingtogether.So,phaseaccumulatorsundertheactionoftheclock,increasingthefrequencycontrolwordtolinearphasetoattack.Canseefromthis,phaseaccumulatorsineachclockpulseinput,thefrequencycontrolwordaccumulatea,phaseaccumulatorsoutputdataisthesignalofthesyntheticphase,phaseaccumulatorsspilloverfrequencyisthesignalfrequencyDDSoutput.Usingphaseaccumulatorsoutputdataaswaveformmemory(ROM)ofthephaseofthesamplingaddress,sojustputthestoredinmemoryofthewaveformsamplingwaveforminvalue(binarycode)findoutbythelook-uptable,completedphasetoamplitudeconversion.TheoutputwaveformmemorytoD/Aconverter,D/Aconverteristhedigitalquantityofthewaveformamplitudeconvertrequiredamountoffrequencysynthesissimulationformsignal.Low-passfilterusedtofilteroutdonotneedtosampleweight,sothattheoutputspectrumpuresinewavesignal.DDSinrelativebandwidth,frequencyconversiontime,highresolution,phasecontinuity,orthogonaloutputandaseriesofintegratedperformanceindexesfarmorethanthetraditionalfrequencysynthesistechnologycanreachthelevel,forthesystemtoprovidethesuperiorperformanceofsimulationsignalsource.
2DDSperformancecharacteristics
(1)theoutputfrequencyrelativebandwidthiswide
Outputfrequencybandwidthfor50%fs(thetheoreticalvalue).Butconsideringthelow-passfilterfeaturesanddesignofdifficultyandtheoutputsignalstraysuppression,theactualoutputfrequencybandwidthstillcanreach40%fs.
(2)frequencyconversiontimeisshort
DDSisaopenloopsystem,withoutanyfeedbackpart,thisstructuremakesDDSoffrequencyconversiontimeisveryshort.Infact,inthefrequencyofDDScontrolwordafterthechangesrequiredtopassthroughaclockcycleaccordingtothenewphaseafterincrementalaccumulate,canrealizefrequencyconversion.Therefore,frequencyconversioncontrolwordfrequencyisequaltothetimeoftransmissiontime,alsoisaclockcycletime.Theclock,thehigherthefrequency,thetransitiontimeisshorter.ThefrequencyconversiontimeDDSDanasecondsordersofmagnitude,thefrequencyofuseotherthansyntheticmethodsareshortseveralordersofmagnitude.
(3)thefrequencyresolutionisextremelyhigh
Iftheclockfrequencyoffschangeless,thefrequencyofDDSbyphaseaccumulatorsresolutionofthedigitsNdecision.AslongastheincreaseofthephaseaccumulatorsdigitsNcanobtainarbitrarilysmallfrequencyresolution.Atpresent,mostoftheresolutionofthe1HzDDSinorderofmagnitude,manylessthan1MHzevensmaller.
(4)continuousphasechanges
ChangeDDSoutputfrequency,infactchangedeachclockcycleofthephaseofthedelta,phasefunctioncurveiscontinuous,justinthefrequencyofthefrequencychangemomenthappenedmutations,sokeepthesignalphasecontinuity.
(5)theflexibilityofoutputwaveform
AslongastheinternalandthecorrespondingcontrolsuchasDDSFMcontrolFM,phase-modulationcontrolPMandanAMcontrolAM,thatcanbeflexibletorealizeFM,jammingandanAMfunction,produceFSK,PSK,ASKandMSKsignaletc.Inaddition,aslongasthewaveformDDSinmemorystoredifferentwaveforms,canachieveallkindsofoutputwaveform,suchastrianglewave,thesawtoothwaveandrectangularwaveevenanywaveform.WhenthewaveformmemorystorageDDSrespectivelysineandcosinefunctionstable,wecangetthetwoorthogonalwayoutput.
(6)otheradvantages
BecauseinalmostallpartsofDDSbelongstothedigitalcircuit,easytointegration,lowpowerconsumption,smallvolume,lightweight,highreliability,andeasytoprogram,useaflexible,sohighperformancetopriceratio.
TwoAT89S52SCMprofile
AT89S52devicesforATMELbytheproductionofalowpowerconsumption,highperformanceCMOS8amicrocontroller,andhas8KinsystemprogrammableFlsahmemory.
1AT89S52devicesmainfunctionlistsareasfollows:
1,haveclever8bitsCPUandinthesystemprogrammableFlash
2,thechipwithinternalclockoscillator(thehighestworkingfrequencytotraditional12MHz)
3,internalprogrammemory(ROM)for8KB
4,internaldatamemory(RAM)for256bytes
5,32programmableI/Omouthline
6,8interruptvectorsource
7,three16timer/counter
8,level3encryptionprogrammemory
9,full-duplexUARTserialchannel
2andAT89S52deviceseachpinfunctionisintroduced:
VCC:
AT89S52devicespoweristheinput,meet+5V.
VSS:
Thepowertoend.
XTAL1:
Singlechipsystemclockofinverseamplifierinputterminal.
XTAL2:
Thesystemclockinverseamplifieroutputterminal,generallyinthedesignaslongasXTAL1andputtheXTAL2inaquartzcrystaloscillationsystemcanaction,inadditiontothetwopinsandtojoina20PFbetweenthesmallcapacitance,canmakethesystemmorestable,avoidnoiseinterferenceandcrash.
RESET:
AT89S52devicesresetpin,highlevelaction,whentochipreset,aslongasthispinleveluptohighlevelandkeeptwomachinecyclemoretime,AT89S51andcanfinishthevariousmovementsofthesystemreset,makeinternalspecialfunctionoftheregistercontentsshallbesettotheknowncondition,andtoaddress0000Hbegantoreadinaprogramcodeandexecutionprocedures.
EA/Vpp:
"EA"forEnglish"ExternalAccess"oftheabbreviations,saidAccessExternalprogramcodeofItaly,lowlevelaction,thatiswhenthispinmeetlowlevel,thesystemwillAccessExternalprogramcode(storedinExternalEPROM)toexecuteaprogram.Soin8031and8032,EApinmustmeetlowlevel,becauseitsinternalnoprogrammemoryspace.Ifistheuseoftheinternalprocess8751space,thepintopickupintohighlevel.Inaddition,theprogramcodein8751whenthedrivetointernalEPROM,canusethepintoinputandVburnhighpressure(Vpp).
ALE/PROG:
ALEisEnglish"AddressLatchEnable"oftheabbreviations,saidAddresslatchesEnablesignal.AT89S52devicescanuseapintotriggertheexternaleightlatches(suchas74LS373),willport0addressbus(A0-A7)lockintothelatches,becauseinmanywaysofAT89S52worksendaddressanddata.AtordinarytimesintheprogramexecutionALEtheoutputofthepinfrequencyisabout1/6oftheworkingfrequencyofthesystem,anditcanbeusedtodrivetheotherperimeterofthechip,andtheinput.Inadditionthedrivein8751theprogramcode,thepinswillbeasthespecialprogrammingfunctiontouse.
PSEN:
Thisas"ProgramStoreEnable"abbreviation,itsmeaningfortheProgramtoStoreopening,when8051weresetbecomeexternalProgramcodereadworkmode(EA=0),willsendthesignalinordertoobtaintheProgramcode,usuallythesupportingfeetisreceivedEPROMOEthefeet.AT89S52devicescanusePSENandRDpinexistingexternalopeningrespectivelyRAMandEPROM,allowthedatastorageandprogrammemorycanbecombinedtogetherandshare64Kaddressedrange.
PORT0(P0.0~P0.7):
Port0isa8bitswideOpenDrain(OpenDrain)two-wayI/oport,atotalofeightbit,P0.0saida0,P0.1saida1,byanalogy.TheotherthreeI/Oport(P1,P2,P3)doesnothavethiscircuitconfiguration,butinternaloneascensioncircuit,P0inasI/OonlycanpusheighttheLSTTLload.IfwhenEApinforlowelectricityatordinarytimes(i.e.accessexternalprogramcodeordatastorage),inmanywaysP0workprovidetheaddressbus(A0-A7)andthedatabus(D0~D7).Thedesignershouldbepluslatcheswillport0sendoutaddressswitchtolockbecomeA0-A7,togetherwiththeport2sendouttheA8~A15tosynthesizeacomplete16theaddressbus,andaddressedtothe64Kexternalmemoryspace.
PORT2(P2.0~P2.7):
Port2isacircuitoftheinternalascensiontwo-wayI/Oport,eachpincanpushfourtheLSTTLload,iftheport2outputsettohighelectricityatordinarytimes,thisportcanbeasinputtouse.ExceptasgeneralP2I/Oportuseoutside,ifintheexternalexpansionprogrammemoryAT89S52ordatastorage,andprovidetheaddressbushighbyteA8~A15,thistimeP2cannotasI/Otouse.
PORT1(P1.0~P1.7):
Port1alsoistohaveinternalascensioncircuittwo-wayI/Oport,theoutputbuffercanpushfourLSTTLload,asiftheport1outputsettohighlevel,isthisporttoinputdata.Ifistousethe8052or8032words,P1.0andastheexternalinputpulsetimer2feet,andP1.1canhaveT2EXfunction,candoexternalinterruptionofinputfeetatrigger.
PORT3(P3.0~P3.7):
Port3alsohaveinternalascensioncircuittwo-wayI/Oport,theoutputbuffercanpushfourTTLload,andalsomanyotheradditionaltoolshavespecialfunction,includingserialcommunication,andexternalinterruption,controlandtimecountcontrolandexternaldatamemoryreadorwritetocontentcontroletc.Function.
Thedistributionofpinsareasfollows:
P3.0:
RXD,serialcommunicationinput.
P3.1:
TXD,serialcommunicationoutput.
P3.2:
INT0,externalinterruption0input.
P3.
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