硬件技术7-2概要

输入/输出接口（2）1四.可编程通信接口16550/82501.RS-232接口标准

DB-25型连接器外形

2

用于异步通信RS-232C的引脚定义*RS-232还有DB-9的连接器3下面介绍RS-232用于异步通信各信号的作用及对应的引脚功能。1．保护地线（引脚1）2．信号地线（引脚7）3．请求发送（引脚4）、清除发送（引脚5）

4．数据设备就绪（引脚6）5．数据终端就绪（引脚20）6．载波检测（引脚8）7．振铃指示（引脚22）8．数据信号速率选择（引脚23）9．发送数据引脚（引脚2）10.接收数据（引脚3）返回本节

RS-232主要功能信号4串行通信接口的典型连接5串行接口适配器由地址译码器、时钟电路、16550/8250UART、数据缓冲器、发送接收驱动器和RS-232插座等组成。由地址译码器接收系统发出的寻址信息，并使能有关的端口寄存器。串行端口COM1和COM2的地址如表所示。其作用为：2.串行接口适配器(接口卡)

串行通信靠发送器、接收器和线缆三部分来实现的。在程序控制下它主要完成以下任务：（1）数据的串——并及并——串转换。（2）线路和MODEM的控制及状态检测。（3）信号电平TTL与EIA电平的转换。（4）发送和接收数据。返回本节6串行通信适配器框图7Auniversalasynchronousreceiver/transmitter(UART).Operationspeed:0-1.5MBaud(Baudis#ofbitstransmitted/sec,includingstart,stop,dataandparity).Includes:•AprogrammableBaudrategenerator.•SeparateFIFObuffersforinputandandoutputdata(16byteseach).Asychronousserialdata:Transmittedandreceivedwithoutaclockortimingsignal.Two10-bitframesofasynchronousdata.7-or8-bitASCII,e.g.worw/oparity,ispossible.3.可编程通信接口芯片16550/8250功能与引脚(DIP40/PLCC40）*FIFO---FirstInFirstOut*PLCC---PlasticLead-lessChipCarrier塑料无引线芯片载体8

Twoseparatesectionsareresponsiblefordatacommunications:ReceiverTransmitterCanfunctionin:simplex:transmitonlyhalf-duplex:transmitandreceivebutnotsimultaneouslyfull-duplex:transmitandreceivesimultaneouslyThe16550cancontrolamodemthroughDSR,DTR,CTS,RTS,RIandDCD.Inthiscontext,themodemiscalledthedatasetwhilethe16550iscalledthedataterminal.可编程通信接口芯片16550引脚信号916550引脚功能A0,A1andA2(input):Selectaninternalregisterforprogramminganddatatransfer.•ADS(input):Addressstrobeusedtolatchaddressandchipselect.NotneededonIntelsystems--connectedtoground.•BAUDOUT(output):ClocksignalfromBaudrategeneratorintransmitter.•CS0,CS1,CS2(input):Chipselects•CTS(input):Cleartosend--indicatesthatthemodemordatasetisreadytoexchangeinformation.(Usedinhalf-duplextoturnthelinearound).10D7-D0(input/output):Thedatabuspinsareconnectedtothemicroprocessordatabus.DCD(input):Thedatacarrierdetect--usedbythemodemtosignalthe16550thatacarrierispresent.DDIS(output):Disabledriveroutput--setto0toindicatethatthemicroprocessorisreadingdatafromtheUART.Usedtochangedirectionofdataflowthroughabuffer.DSR(input):Datasetreadyisaninputto16550--indicatesthatthemodem(dataset)isreadytooperate.DTR(output):Dataterminalreadyisanoutput--indicatesthatthedataterminal(16550)isreadytofunction.INTR(output):Interruptrequestisanoutputtothemicro--usedtorequestaninterrupt.ReceivererrorDatareceivedTransmitbufferempty11MR(input):Masterreset--connecttosystemRESETOUT1,OUT2(output):Userdefinedoutputpinsformodemorotherdevice.RCLK(input):Receiverclock--clockinputtothereceiversectionoftheUART.Always16XthedesiredreceiverBaudrate.RD,RD(input):Readinputs(eithercanbeused)--causedatatobereadfromtheregistergivenbytheaddressinputs.RI(input):Ringindicatorinput--setto0bymodemtoindicatetelephoneisringing.RTS(output):Request-to-send--signaltomodem,indicatingUARTwishestosenddata.SIN(input),SOUT(output):Serialdatapins,inandout.RXRDY(input):Receiverready--usedtotransferreceiveddataviaDMAtechniques.TXRDY(output):Transmitterready--usedtotransfertransmitterdataviaDMA.WR,WR(input):Write(eithercanbeused)--connectstomicrowritesignaltotransfercommandsanddatato16550.XIN,XOUT:Mainclockconnections--acrystaloscillatorcanbeused.12

16550电路应用连接与8088微处理器连接，端口地址为00F0H~00F7H的165501316550/8250UART内部寄存器框图4.16550/8250UART内部寄存器14中断允许寄存器(A2A1A0=001)•中断标识寄存器(A2A1A0=010)15FIFO控制寄存器(A2A1A0=010)初始化FIFO的状态16线路控制寄存器(A2A1A0=011)设定串行数据格式和波特率17线路状态寄存器(A2A1A0=101)发送或接收时查询是否准备就绪，有否错误185.编程与控制5.1初始化---编程线路控制寄存器、波特率发生器和FIFOTwophases:Initialization,operation.Initialization:AfterRESET,thelinecontrolregisterandbaudrategeneratorneedtobeprogrammed.Linecontrolregistersetsthe#ofdatabits,#ofstopbitsandtheparity.Addressedatlocation011.Stopbits:S=1,1.5stopbitsusedfor5databits,2usedfor6,7or8.19Initialization(cont.)ST,PandPEusedtosendevenoroddparity,tosendnoparityortosenda1ora0intheparitybitpositionforalldata.Noparity,both0--usedforinternetconnections.SB=1causesabreaktobetransmittedonSOUT.Abreakisatleasttwoframeof0data.DL=1enablesprogrammingofthebaudratedivisor.20Initialization(cont.)Baudrategeneratorisprogrammedwithadivisorthatsetsbaudrateoftransmitter.Baudrategeneratorisprogrammedat000and001.Port000usedtoholdleastsignificantbyte,001mostsignificant.Valueuseddependsonexternalclock/crystalfrequency.For18.432MHzcrystal,10,473gives110bandrate,30gives38,400baud.Note,numberprogrammedgeneratesaclock16XthedesiredBaudrate.Last,theFIFOcontrolregistermustbeprogrammedat010.21

波特率与除数寄存器值的关系*波特率=晶体频率/(N*除数值)-----N取1，16，32等*本例若选取晶体频率为18.432MHZ，N=16，则除数值应乘以1022PC系统中串行端口寄存器地址23例：一个异步系统需要7位数据位、奇校验、9600的波特率及1位停止位，端口地址为3F8H~3FFH（COM1），其初始化程序为

LINEEQU3FBH；线路控制寄存器

LSBEQU3F8H；波特率除数寄存器低位

MSBEQU3F9H；波特率除数寄存器高位

FIFOEQU3FAH；FIFO控制寄存器

STARTPROCNEARMOVAL，10001010B；允许除数锁存

MOVDX，LINE

指向除数寄存器

OUTDX，AL24

MOVAL，120；除数值120，波特率9600

MOVDX，LSBOUTDX，ALINCDX；指向高位

MOVAL，0OUTDX，AL

INCDX；指向线路控制寄存器

INCDXMOVAL，00001010B；7位数据位

OUTDX，AL

1位停止位，奇校验

无间隔发送

25

MOVAL，00000111B；初始化FIFO，FIFO使能

DECDX清除接收器/发送器

OUTDX，AL

RETSTARTENDP5.2发送串行数据---线路状态寄存器、发送器锁存26Operating:Statuslineregistergivesinformationabouterrorconditionsandstateofthetransmitterandreceiver.Thisregisterneedstobetestedinsoftwareroutinesdesignedtousethe16550totransmit/receivedata.SupposeaprogramwantstosenddataoutSOUT.ItneedstopooltheTHbittodetermineiftransmitterisreadytoreceivedata.Toreceiveinformation,theDRbitistested.27例：将AH的内容发送给16550并通过其串行数据引脚SOUT输出，其程序为

LSTATEQU3FDH；线路状态寄存器

DATAEQU3F8H；发送器锁存

SENDPROCNEARPUSHAXPUSHDXSEND1：MOVDX，LSTATINAL，DX；读线路状态

TESTAL，20H；测试TH位

JZSEND1；等待发送器准备就绪28

MOVAL，AH；取数据

SUBDX，5；指向发送器锁存

OUTDX，AL；发送数据

POPDXPOPAXRETSENDENDP5.3接收串行数据---线路状态寄存器、接收缓冲器29Operating:Itisalsoagoodideatocheckforerrors.Parityerror（1）:Receiveddatahaswrongerror--transmissionbitflipduetonoise.Framingerror（1）:Startandstopbitsnotintheirproperplaces.Thisusuallyresultsifthereceiverisreceivingdataattheincorrectbaudrate.Overrunerror（1）:DatahasoverruntheinternalreceiverFIFObuffer.SoftwareisfailingtoreadthedatafromtheFIFO.Breakindicatorbit:Softwareshouldcheckforthisaswell,i.e.twoconsecutiveframesof0s..30例：从16550中读取接收到的信息，若检测到一个错误，则在AL中返回一个ASCII码‘？’，若无错误，则在AL中返回接收到的字符。其程序为

LSTATEQU3FDH