基于at89c52单片机的交通灯控制系统设计(外文翻译)

电子与信息工程学院本科毕业论文设计外文文献翻译译文题目8BITMICROCONTROLLERWITH8KBYTESFLASHAT89C52学生姓名吴远超专业电气工程及其自动化指导教师倪浩2012年11月外文资料8BITMICROCONTROLLERWITH8KBYTESFLASHAT89C52FEATURESCOMPATIBLEWITHMCS51PRODUCTS8KBYTESOFINSYSTEMREPROGRAMMABLEFLASHMEMORYENDURANCE1,000WRITE/ERASECYCLESFULLYSTATICOPERATION0HZTO24MHZTHREELEVELPROGRAMMEMORYLOCK256X8BITINTERNALRAM32PROGRAMMABLEI/OLINESTHREE16BITTIMER/COUNTERSEIGHTINTERRUPTSOURCESPROGRAMMABLESERIALCHANNELLOWPOWERIDLEANDPOWERDOWNMODESDESCRIPTIONTHEAT89C52ISALOWPOWER,HIGHPERFORMANCECMOS8BITMICROCOMPUTERWITH8KBYTESOFFLASHPROGRAMMABLEANDERASABLEREADONLYMEMORYPEROMTHEDEVICEISMANUFACTUREDUSINGATMELSHIGHDENSITYNONVOLATILEMEMORYTECHNOLOGYANDISCOMPATIBLEWITHTHEINDUSTRYSTANDARD80C51AND80C52INSTRUCTIONSETANDPINOUTTHEONCHIPFLASHALLOWSTHEPROGRAMMEMORYTOBEREPROGRAMMEDINSYSTEMORBYACONVENTIONALNONVOLATILEMEMORYPROGRAMMERBYCOMBININGAVERSATILE8BITCPUWITHFLASHONAMONOLITHICCHIP,THEATMELAT89C52ISAPOWERFULMICROCOMPUTERWHICHPROVIDESAHIGHLYFLEXIBLEANDCOSTEFFECTIVESOLUTIONTOMANYEMBEDDEDCONTROLAPPLICATIONSPINCONFIGURATIONSBLOCKDIAGRAMPINDESCRIPTIONVCCSUPPLYVOLTAGEGNDGROUNDPORT0PORT0ISAN8BITOPENDRAINBIDIRECTIONALI/OPORTASANOUTPUTPORT,EACHPINCANSINKEIGHTTTLINPUTSWHEN1SAREWRITTENTOPORT0PINS,THEPINSCANBEUSEDASHIGHIMPEDANCEINPUTSPORT0CANALSOBECONFIGUREDTOBETHEMULTIPLEXEDLOWORDERADDRESS/DATABUSDURINGACCESSESTOEXTERNALPROGRAMANDDATAMEMORYINTHISMODE,P0HASINTERNALPULLUPSPORT0ALSORECEIVESTHECODEBYTESDURINGFLASHPROGRAMMINGANDOUTPUTSTHECODEBYTESDURINGPROGRAMVERIFICATIONEXTERNALPULLUPSAREREQUIREDDURINGPROGRAMVERIFICATIONPORT1PORT1ISAN8BITBIDIRECTIONALI/OPORTWITHINTERNALPULLUPSTHEPORT1OUTPUTBUFFERSCANSINK/SOURCEFOURTTLINPUTSWHEN1SAREWRITTENTOPORT1PINS,THEYAREPULLEDHIGHBYTHEINTERNALPULLUPSANDCANBEUSEDASINPUTSASINPUTS,PORT1PINSTHATAREEXTERNALLYBEINGPULLEDLOWWILLSOURCECURRENTIILBECAUSEOFTHEINTERNALPULLUPSINADDITION,P10ANDP11CANBECONFIGUREDTOBETHETIMER/COUNTER2EXTERNALCOUNTINPUTP10/T2ANDTHETIMER/COUNTER2TRIGGERINPUTP11/T2EX,RESPECTIVELY,ASSHOWNINTHEFOLLOWINGTABLEPORT1ALSORECEIVESTHELOWORDERADDRESSBYTESDURINGFLASHPROGRAMMINGANDVERIFICATIONPORT2PORT2ISAN8BITBIDIRECTIONALI/OPORTWITHINTERNALPULLUPSTHEPORT2OUTPUTBUFFERSCANSINK/SOURCEFOURTTLINPUTSWHEN1SAREWRITTENTOPORT2PINS,THEYAREPULLEDHIGHBYTHEINTERNALPULLUPSANDCANBEUSEDASINPUTSASINPUTS,PORT2PINSTHATAREEXTERNALLYBEINGPULLEDLOWWILLSOURCECURRENTIILBECAUSEOFTHEINTERNALPULLUPSPORT2EMITSTHEHIGHORDERADDRESSBYTEDURINGFETCHESFROMEXTERNALPROGRAMMEMORYANDDURINGACCESSESTOEXTERNALDATAMEMORIESTHATUSE16BITADDRESSESMOVXDPTRINTHISAPPLICATION,PORT2USESSTRONGINTERNALPULLUPSWHENEMITTING1SDURINGACCESSESTOEXTERNALDATAMEMORIESTHATUSE8BITADDRESSESMOVXRI,PORT2EMITSTHECONTENTSOFTHEP2SPECIALFUNCTIONREGISTERPORT2ALSORECEIVESTHEHIGHORDERADDRESSBITSANDSOMECONTROLSIGNALSDURINGFLASHPROGRAMMINGANDVERIFICATIONPORT3PORT3ISAN8BITBIDIRECTIONALI/OPORTWITHINTERNALPULLUPSTHEPORT3OUTPUTBUFFERSCANSINK/SOURCEFOURTTLINPUTSWHEN1SAREWRITTENTOPORT3PINS,THEYAREPULLEDHIGHBYTHEINTERNALPULLUPSANDCANBEUSEDASINPUTSASINPUTS,PORT3PINSTHATAREEXTERNALLYBEINGPULLEDLOWWILLSOURCECURRENTIILBECAUSEOFTHEPULLUPSPORT3ALSOSERVESTHEFUNCTIONSOFVARIOUSSPECIALFEATURESOFTHEAT89C51,ASSHOWNINTHEFOLLOWINGTABLEPORT3ALSORECEIVESSOMECONTROLSIGNALSFORFLASHPROGRAMMINGANDVERIFICATIONRSTRESETINPUTAHIGHONTHISPINFORTWOMACHINECYCLESWHILETHEOSCILLATORISRUNNINGRESETSTHEDEVICEALE/PROGADDRESSLATCHENABLEISANOUTPUTPULSEFORLATCHINGTHELOWBYTEOFTHEADDRESSDURINGACCESSESTOEXTERNALMEMORYTHISPINISALSOTHEPROGRAMPULSEINPUTPROGDURINGFLASHPROGRAMMINGINNORMALOPERATION,ALEISEMITTEDATACONSTANTRATEOF1/6THEOSCILLATORFREQUENCYANDMAYBEUSEDFOREXTERNALTIMINGORCLOCKINGPURPOSESNOTE,HOWEVER,THATONEALEPULSEISSKIPPEDDURINGEACHACCESSTOEXTERNALDATAMEMORYIFDESIRED,ALEOPERATIONCANBEDISABLEDBYSETTINGBIT0OFSFRLOCATION8EHWITHTHEBITSET,ALEISACTIVEONLYDURINGAMOVXORMOVCINSTRUCTIONOTHERWISE,THEPINISWEAKLYPULLEDHIGHSETTINGTHEALEDISABLEBITHASNOEFFECTIFTHEMICROCONTROLLERISINEXTERNALEXECUTIONMODEPSENPROGRAMSTOREENABLEISTHEREADSTROBETOEXTERNALPROGRAMMEMORYWHENTHEAT89C52ISEXECUTINGCODEFROMEXTERNALPROGRAMMEMORY,ISACTIVATEDTWICEPSENEACHMACHINECYCLE,EXCEPTTHATTWOACTIVATIONSARESKIPPEDDURINGEACHPSENACCESSTOEXTERNALDATAMEMORY/VPPEAEXTERNALACCESSENABLEMUSTBESTRAPPEDTOGNDINORDERTOENABLETHEEADEVICETOFETCHCODEFROMEXTERNALPROGRAMMEMORYLOCATIONSSTARTINGAT0000HUPTOFFFFHNOTE,HOWEVER,THATIFLOCKBIT1ISPROGRAMMED,WILLBEINTERNALLYEALATCHEDONRESETEASHOULDBESTRAPPEDTOVCCFORINTERNALPROGRAMEXECUTIONSTHISPINALSORECEIVESTHE12VOLTPROGRAMMINGENABLEVOLTAGEVPPDURINGFLASHPROGRAMMINGWHEN12VOLTPROGRAMMINGISSELECTEDXTAL1INPUTTOTHEINVERTINGOSCILLATORAMPLIFIERANDINPUTTOTHEINTERNALCLOCKOPERATINGCIRCUITXTAL2OUTPUTFROMTHEINVERTINGOSCILLATORAMPLIFIERSPECIALFUNCTIONREGISTERSAMAPOFTHEONCHIPMEMORYAREACALLEDTHESPECIALFUNCTIONREGISTERSFRSPACEISSHOWNINTHETABLE1NOTETHATNOTALLOFTHEADDRESSESAREOCCUPIED,ANDUNOCCUPIEDADDRESSESMAYNOTBEIMPLEMENTEDONTHECHIPREADACCESSESTOTHESEADDRESSESWILLINGENERALRETURNRANDOMDATA,ANDWRITEACCESSESWILLHAVEANINDETERMINATEEFFECTUSERSOFTWARESHOULDNOTWRITE1STOTHESEUNLISTEDLOCATIONS,SINCETHEYMAYBEUSEDINFUTUREPRODUCTSTOINVOKENEWFEATURESINTHATCASE,THERESETORINACTIVEVALUESOFTHENEWBITSWILLALWAYSBE0TIMER2REGISTERSCONTROLANDSTATUSBITSARECONTAINEDINREGISTERST2CONANDT2MODFORTIMER2THEREGISTERPAIRRCAP2H,RCAP2LARETHECAPTURE/RELOADREGISTERSFORTIMER2IN16BITCAPTUREMODEOR16BITAUTORELOADMODEINTERRUPTREGISTERSTHEINDIVIDUALINTERRUPTENABLEBITSAREINTHEIEREGISTERTWOPRIORITIESCANBESETFOREACHOFTHESIXINTERRUPTSOURCESINTHEIPREGISTERDATAMEMORYTHEAT89C52IMPLEMENTS256BYTESOFONCHIPRAMTHEUPPER128BYTESOCCUPYAPARALLELADDRESSSPACETOTHESPECIALFUNCTIONREGISTERSTHATMEANSTHEUPPER128BYTESHAVETHESAMEADDRESSESASTHESFRSPACEBUTAREPHYSICALLYSEPARATEFROMSFRSPACEWHENANINSTRUCTIONACCESSESANINTERNALLOCATIONABOVEADDRESS7FH,THEADDRESSMODEUSEDINTHEINSTRUCTIONSPECIFIESWHETHERTHECPUACCESSESTHEUPPER128BYTESOFRAMORTHESFRSPACEINSTRUCTIONSTHATUSEDIRECTADDRESSINGACCESSSFRSPACEFOREXAMPLE,THEFOLLOWINGDIRECTADDRESSINGINSTRUCTIONACCESSESTHESFRATLOCATION0A0HMOV0A0H,DATAINSTRUCTIONSTHATUSEINDIRECTADDRESSINGACCESSTHEUPPER128BYTESOFRAMFOREXAMPLE,THEFOLLOWINGINDIRECTADDRESSINGINSTRUCTION,WHERER0CONTAINS0A0H,ACCESSESTHEDATABYTEATADDRESS0A0H,RATHERTHANP2WHOSEADDRESSIS0A0HMOVR0,DATANOTETHATSTACKOPERATIONSAREEXAMPLESOFINDIRECTADDRESSING,SOTHEUPPER128BYTESOFDATARAMAREAVAILABLEASSTACKSPACETIMER0AND1TIMER0ANDTIMER1INTHEAT89C52OPERATETHESAMEWAYASTIMER0ANDTIMER1INTHEAT89C51TIMER2TIMER2ISA16BITTIMER/COUNTERTHATCANOPERATEASEITHERATIMERORANEVENTCOUNTERTHETYPEOFOPERATIONISSELECTEDBYBITC/T2INTHESFRT2CONTIMER2HASTHREEOPERATINGMODESCAPTURE,AUTORELOADUPORDOWNCOUNTING,ANDBAUDRATEGENERATORTHEMODESARESELECTEDBYBITSINT2CON,ASSHOWNINTABLE3TIMER2CONSISTSOFTWO8BITREGISTERS,TH2ANDTL2INTHETIMERFUNCTION,THETL2REGISTERISINCREMENTEDEVERYMACHINECYCLESINCEAMACHINECYCLECONSISTSOF12OSCILLATORPERIODS,THECOUNTRATEIS1/12OFTHEOSCILLATORFREQUENCYINTHECOUNTERFUNCTION,THEREGISTERISINCREMENTEDINRESPONSETOA1TO0TRANSITIONATITSCORRESPONDINGEXTERNALINPUTPIN,T2INTHISFUNCTION,THEEXTERNALINPUTISSAMPLEDDURINGS5P2OFEVERYMACHINECYCLEWHENTHESAMPLESSHOWAHIGHINONECYCLEANDALOWINTHENEXTCYCLE,THECOUNTISINCREMENTEDTHENEWCOUNTVALUEAPPEARSINTHEREGISTERDURINGS3P1OFTHECYCLEFOLLOWINGTHEONEINWHICHTHETRANSITIONWASDETECTEDSINCETWOMACHINECYCLES24OSCILLATORPERIODSAREREQUIREDTORECOGNIZEA1TO0TRANSITION,THEMAXIMUMCOUNTRATEIS1/24OFTHEOSCILLATORFREQUENCYTOENSURETHATAGIVENLEVELISSAMPLEDATLEASTONCEBEFOREITCHANGES,THELEVELSHOULDBEHELDFORATLEASTONEFULLMACHINECYCLECAPTUREMODEINTHECAPTUREMODE,TWOOPTIONSARESELECTEDBYBITEXEN2INT2CONIFEXEN20,TIMER2ISA16BITTIMERORCOUNTERWHICHUPONOVERFLOWSETSBITTF2INT2CONTHISBITCANTHENBEUSEDTOGENERATEANINTERRUPTIFEXEN21,TIMER2PERFORMSTHESAMEOPERATION,BUTA1TO0TRANSITIONATEXTERNALINPUTT2EXALSOCAUSESTHECURRENTVALUEINTH2ANDTL2TOBECAPTUREDINTORCAP2HANDRCAP2L,RESPECTIVELYINADDITION,THETRANSITIONATT2EXCAUSESBITEXF2INT2CONTOBESETTHEEXF2BIT,LIKETF2CANGENERATEANINTERRUPTTHECAPTUREMODEISILLUSTRATEDINFIGURE1AUTORELOADUPORDOWNCOUNTERTIMER2CANBEPROGRAMMEDTOCOUNTUPORDOWNWHENCONFIGUREDINITS16BITAUTORELOADMODETHISFEATUREISINVOKEDBYTHEDCENDOWNCOUNTERENABLEBITLOCATEDINTHESFRT2MODUPONRESET,THEDCENBITISSETTO0SOTHATTIMER2WILLDEFAULTTOCOUNTUPWHENDCENISSET,TIMER2CANCOUNTUPORDOWN,DEPENDINGONTHEVALUEOFTHET2EXPINFIGURE2SHOWSTIMER2AUTOMATICALLYCOUNTINGUPWHENDCEN0INTHISMODE,TWOOPTIONSARESELECTEDBYBITEXEN2INT2CONIFEXEN20,TIMER2COUNTSUPTO0FFFFHANDTHENSETSTHETF2BITUPONOVERFLOWTHEOVERFLOWALSOCAUSESTHETIMERREGISTERSTOBERELOADEDWITHTHE16BITVALUEINRCAP2HANDRCAP2LTHEVALUESINTIMERINCAPTUREMODERCAP2HANDRCAP2LAREPRESETBYSOFTWAREIFEXEN21,A16BITRELOADCANBETRIGGEREDEITHERBYANOVERFLOWORBYA1TO0TRANSITIONATEXTERNALINPUTT2EXTHISTRANSITIONALSOSETSTHEEXF2BITBOTHTHETF2ANDEXF2BITSCANGENERATEANINTERRUPTIFENABLEDSETTINGTHEDCENBITENABLESTIMER2TOCOUNTUPORDOWN,ASSHOWNINFIGURE3INTHISMODE,THET2EXPINCONTROLSTHEDIRECTIONOFTHECOUNTALOGIC1ATT2EXMAKESTIMER2COUNTUPTHETIMERWILLOVERFLOWAT0FFFFHANDSETTHETF2BITTHISOVERFLOWALSOCAUSESTHE16BITVALUEINRCAP2HANDRCAP2LTOBERELOADEDINTOTHETIMERREGISTERS,TH2ANDTL2,RESPECTIVELYALOGIC0ATT2EXMAKESTIMER2COUNTDOWNTHETIMERUNDERFLOWSWHENTH2ANDTL2EQUALTHEVALUESSTOREDINRCAP2HANDRCAP2LTHEUNDERFLOWSETSTHETF2BITANDCAUSES0FFFFHTOBERELOADEDINTOTHETIMERREGISTERSTHEEXF2BITTOGGLESWHENEVERTIMER2OVERFLOWSORUNDERFLOWSANDCANBEUSEDASA17THBITOFRESOLUTIONINTHISOPERATINGMODE,EXF2DOESNOTFLAGANINTERRUPT外文资料译文8位8字节闪存单片机AT89C52主要性能与MCS51单片机产品兼容8K字节在系统可编程FLASH存储器1000次擦写周期全静态操作0HZ24HZ三级加密程序存储器2568位内部存储器32个可编程I/O口线三个16位定时器/计数器八个中断源可编程串行通道低功耗空闲和掉电模式功能特性描述AT89S52是一种低功耗、高性能CMOS8位微控制器，具有8K内置可编程闪存。产品使用了ATMEL公司高密度非易失性存储器技术制造，与工业80C51和80C52产品指令和引脚完全兼容。片上FLASH允许程序存储器在系统可编程，亦适于常规编程器。在单芯片上，拥有灵巧的8位CPU和在系统可编程FLASH，使得AT89S52为众多嵌入式控制应用系统提供高灵活、超有效的解决方案。引脚结构方框图VCC电源GND地P0口P0口是一个8位漏极开路的双向I/O口。作为输出口，每位能驱动8个TTL逻辑电平。对P0端口写“1”时，引脚用作高阻抗输入。当访问外部程序和数据存储器时，P0口也被作为低8位地址/数据复用。在这种模式下，P0具有内部上拉电阻。在FLASH编程时，P0口也用来接收指令字节；在程序校验时，输出指令字节。程序校验时，需要外部上拉电阻。P1口P1口是一个具有内部上拉电阻的8位双向I/O口，P1输出缓冲器能驱动4个TTL逻辑电平。对P1端口写“1”时，内部上拉电阻把端口拉高，此时可以作为输入口使用。作为输入使用时，被外部拉低的引脚由于内部电阻的原因，将输出电流（IIL）。此外，P10和P12分别作定时器/计数器2的外部计数输入（P10/T2）和时器/计数器2的触发输入（P11/T2EX），具体如下表所示。在FLASH编程和校验时，P1口接收低8位地址字节。P2口P2口是一个具有内部上拉电阻的8位双向I/O口，P2输出缓冲器能驱动4个TTL逻辑电平。对P2端口写“1”时，内部上拉电阻把端口拉高，此时可以作为输入口使用。作为输入使用时，被外部拉低的引脚由于内部电阻的原因，将输出电流（IIL）。在访问外部程序存储器或用16位地址读取外部数据存储器（例如执行MOVXDPTR）时，P2口送出高八位地址。在这种应用中，P2口使用很强的内部上拉发送1。在使用8位地址（如MOVXRI）访问外部数据存储器时，P2口输出P2锁存器的内容。在FLASH编程和校验时，P2口也接收高8位地址字节和一些控制信号。P3口P3口是一个具有内部上拉电阻的8位双向I/O口，P2输出缓冲器能驱动4个TTL逻辑电平。对P3端口写“1”时，内部上拉电阻把端口拉高，此时可以作为输入口使用。作为输入使用时，被外部拉低的引脚由于内部电阻的原因，将输出电流（IIL）。P3口亦作为AT89S52特殊功能（第二功能）使用，如下表所示。在FLASH编程和校验时，P3口也接收一些控制信号。RST复位输入。晶振工作时，RST脚持续2个机器周期高电平将使单片机复位。看门狗计时完成后，RST脚输出96个晶振周期的高电平。特殊寄存器AUXR地址8EH上的DISRTO位可以使此功能无效。DISRTO默认状态下，复位高电平有效。ALE/地址锁存控制信号（ALE）是访问外部程序存储器时，锁存低8PROG位地址的输出脉冲。在FLASH编程时，此引脚（）也用作编程输入脉冲。PROG在一般情况下，ALE以晶振六分之一的固定频率输出脉冲，可用来作为外部定时器或时钟使用。然而，特别强调，在每次访问外部数据存储器时，ALE脉冲将会跳过。如果需要，通过将地址为8EH的SFR的第0位置“1”，ALE操作将无效。这一位置“1”，ALE仅在执行MOVX或MOVC指令时有效。否则，ALE将被微弱拉高。这个ALE使能标志位（地址为8EH的SFR的第0位）的设置对微控制器处于外部执行模式下无效。外部程序存储器选通信号（）是外部程序存储器选通信号。PSENPSEN当AT89S52从外部程序存储器执行外部代码时，在每个机器周期被激活两PSEN次，而在访问外部数据存储器时，将不被激活。PSEN/VPP访问外部程序存储器控制信号。为使能从0000H到FFFFH的外部程EA序存储器读取指令，必须接GND。为了执行内部程序指令，应该接VCC。EAEA在FLASH编程期间，也接收12伏VPP电压。EAXTAL1振荡器反相放大器和内部时钟发生电路的输入端。XTAL2振荡器反相放大器的输出端。特殊功能寄存器如图1中所示的存储器区域称为特殊功能寄存器。应该注意到，并不是所有的地址都会被定义，单片机中那些没有被定义的地址是无效的。读访问这些地址一般会返回随机数据，写访问这些地址则会产生一个不确定的影响。用户软件不应将那些没有被列举出来的地址置1。在这种情况下，复位后这些单元数值总是0。定时/计数器2定时/计数器2的控制和状态位位于T2CON和T2MOD。寄存器对（RCAO2H、RCAP2L）是定时器2在16位捕获方式或16位自动重装载方式下的捕获/自动重装载寄存器。中断寄存器所有单独的中断允许位都存在于中断允许寄存器IE中。中断优先级寄存器IP可以为六个中断源设置两个中断优先级。数据存储器AT89C52实现256字节片上RAM。高128个字节与特殊功能寄存器（SFR）地址是重叠的，也就是高128字节的RAM和特殊功能寄存器的地址是相同的,但物理上它们是分开的。当一条指令访问7FH以上的内部地址单元时，指令中使用的寻址方式是不同的，也即寻址方式决定是访问高128字节RAM还是访问特殊功能寄存器。如果指令是直接寻址方式则为访问特殊功能寄存器。例如，下面的直接寻址指令访问特殊功能寄存器0A0H（即P2口）地址单元。MOV0A0H，DATA间接寻址指令访问高128字节RAM，例如，下面的间接寻址指令中，R0的内容为0A0H，则访问数据字节地址为0A0H，而不是P2口（0A0H）。MOVR0，DATA堆栈操作也是间接寻址方式，所以，高128位数据RAM亦可作为堆栈区使用。定时器0/定时器1AT89C52的定时器0和定时器1的工作方式与AT89C51相同。定时器2定时器2是一个16位定时/计数器。它既可当定时器使用，也可作为外部事件计数器使用，其工作方式由特殊功能寄存器T2CON（如表3）的C/T2位选择。定时器2有三种工作方式捕获方式，自动重装载（向上或向下计数）方式和波特率发生器方式，工作方式由T2CON的控制位来选择。定时器2由两个8位寄存器TH2和TL2组成，在定时器工作方式中，每个机器周期TL2寄存器的值加1，由于一个机器周期由12个振荡时钟构成，因此，计数速率为振荡频率的1/12。RCLKTCLKCP/RL2TR2MODE00116BITAUTORELOAD01116BITCAPTURE1X1BAUDRATEGENERATORXX0OFF在计数工作方式时，当T2引脚上外部输入信号产生由1至0的下降沿时，寄存器的值加1，在这种工作方式下，每个机器周期的5SP2期间，对外部输入进行采样。若在第一个机器周期中采到的值为1，而在下一个机器周期中采到的值为0，则在紧跟着的下一个周期的S3P1期间寄存器加1。由于识别1至0的跳变需要2个机器周期（24个振荡周期），因此，最高计数速率为振荡频率的1/24。为确保采样的正确性，要求输入的电平在变化前至少保持一个完整周期的时间，以保证输入信号至少被采样一次。捕获方式在捕获方式下，通过T2CON控制位EXEN2来选择两种方式。如果EXEN20，定时器2是一个16位定时器或计数器，计数溢出时，对T2CON的溢出标志TF2置位，同时激活中断。如果EXEN21，定时器2完成相同的操作，而当T2EX引脚外部输入信号发生1至0负跳变时，也出现TH2和TL2中的值分别被捕获到RCAP2H和RCAP2L中。另外，T2EX引脚信号的跳变使得T2CON中的EXF2置位，与TF2相仿，EXF2也会激活中断。自动重装载（向上或向下计数器）方式当定时器2工作于16位自动重装载方式时，能对其编程为向上或向下计数方式，这个功能可通过特殊功能寄存器T2CON的DCEN位（允许向下计数）来选择的。复位时，DCEN位置“0”，定时器2默认设置为向上计数。当DCEN置位时，定时器2既可向上计数也可向下计数，这取决于T2EX引脚的值。当DCEN0时，定时器2自动设置为向上计数，在这种方式下，T2CON中的EXEN2控制位有两种选择，若EXEN20，定时器2为向上计数至0FFFFH溢出，置位TF2激活中断，同时把16位计数寄存器RCAP2H和RCAP2L重装载，RCAP2H和RCAP2L的值可由软件预置。若EXEN21，定时器2的16位重装载由溢出或外部输入端T2EX从1至0的下降沿触发。这个脉冲使EXF2置位，如果中断允许，同样产生中断。定时器2的中断入口地址是002BH0032H。当DCEN1时，允许定时器2向上或向下计数，如图6所示。这种方式下，T2EX引脚控制计数器方向。T2EX引脚为逻辑“1”时，定时器向上计数，当计数0FFFFH向上溢出时，置位TF2，同时把16位计数寄存器RCAP2H和RCAP2L重装载到TH2和TL2中。T2EX引脚为逻辑“0”时，定时器2向下计数，当TH2和TL2中的数值等于RCAP2H和RCAP2L中的值时，计数溢出，置位TF2，同时将0FFFFH数值重新装入定时寄存器中。当定时/计数器2向上溢出或向下溢出时，置位EXF2位。AGANEMPLOYMENTTRIBUNALCLAIEMLOYMENTTRIBUNALSSORTOUTDISAGREEMENTSBETWEENEMPLOYERSANDEMPLOYEESYOUMAYNEEDTOMAKEACLAIMTOANEMPLOYMENTTRIBUNALIFYOUDONTAGREEWITHTHEDISCIPLINARYACTIONYOUREMPLOYERHASTAKENAGAINSTYOUYOUREMPLOYERDISMISSESYOUANDYOUTHINKTHATYOUHAVEBEENDISMISSEDUNFAIRLYFORMOREINFORMU,TAKEADVICEFROMONEOFTHEORGANISATIONSLISTEDUNDERFURTHERHELPEMPLOYMENTTRIBUNALSARELESSFORMALTHANSOMEOTHERCOURTS,BUTITISSTILLALEGALPROCESSANDYOUWILLNEEDTOGIVEEVIDENCEUNDERANOATHORAFFIRMATIONMOSTPEOPLEFINDMAKINGACLAIMTOANEMPLOYMENTTRIBUNALCHALLENGINGIFYOUARETHINKINGABOUTMAKINGACLAIMTOANEMPLOYMENTTRIBUNAL,YOUSHOULDGETHELPSTRAIGHTAWAYFROMONEOFTHEORGANISATIONSLISTEDUNDERFURTHERHELPATIONABOUTDISMISSALANDUNFAIRDISMISSAL,SEEDISMISSALYOUCANMAKEACLAIMTOANEMPLOYMENTTRIBUNAL,EVENIFYOUHAVENTAPPEALEDAGAINSTTHEDISCIPLINARYACTIONYOUREMPLOYERHASTAKENAGAINSTYOUHOWEVER,IFYOUWINYOURCASE,THETRIBUNALMAYREDUCEANYCOMPENSATIONAWARDEDTOYOUASARESULTOFYOURFAILURETOAPPEALREMEMBERTHATINMOSTCASESYOUMUSTMAKEANAPPLICATIONTOANEMPLOYMENTTRIBUNALWITHINTHREEMONTHSOFTHEDATEWHENTHEEVENTYOUARECOMPLAININGABOUTHAPPENEDIFYOURAPPLICATIONISRECEIVEDAFTERTHISTIMELIMIT,THETRIBUNALWILLNOTUSUALLYACCEPTIIFYOUAREWORRIEDABOUTHOWTHETIMELIMITSAPPLYTOYOUIFYOUAREBEINGREPRESENTEDBYASOLICITORATTHETRIBUNAL,THEYMAYASKYOUTOSIGNANAGREEMENTWHEREYOUPAYTHEIRFEEOUTOFYOURCOMPENSATIONIFYOUWINTHECASETHISISKNOWNASADAMAGESBASEDAGREEMENTINENGLANDANDWALES,YOURSOLICITORCANTCHARGEYOUMORETHAN35OFYOURCOMPENSATIONIFYOUWINTHECASEYOURECLEARABOUTTHETERMSOFTHEAGREEMENTITMIGHTBEBESTTOGETADVICEFROMANEXPERIENCEDADVISER,FOREXAMPLE,ATACITIZENSADVICEBUREAUTOFINDYOURNEARESTCAB,INCLUDINGTHOSETHATGIVEADVICEBYEMAIL,CLICKONNEARESTCABFORMOREINFORMATIONABOUTMAKINGACLAIMTOANEMPLOYMENTTRIBUNAL,SEEEMPLOYMENTTRIBUNALSTHELACKOFAIRUPTHEREWATCHMCAYMANISLANDSBASEDWEBB,THEHEADOFFIFASANTIRACISMTASKFORCE,ISINLONDONFORTHEFOOTBALLASSOCIATIONS150THANNIVERSARYCELEBRATIONSANDWILLATTENDCITYSPREMIERLEAGUEMATCHATCHELSEAONSUNDAY“IAMGOINGTOBEA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