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HT67F488 Datasheet(PDF) 122 Page - Holtek Semiconductor Inc |
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HT67F488 Datasheet(HTML) 122 Page - Holtek Semiconductor Inc |
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122 / 171 page  Rev. 1.60 1�� �ove��e� ��� �016 HT67F488/HT67F489 TinyPowerTM A/D Flash MCU with LCD & EEPROM UART Transmitter Datawordlengthsofeither8or9bitscanbeselectedbyprogrammingtheBNObitintheUCR1 register.WhenBNObitisset,thewordlengthwillbesetto9bits.Inthiscasethe9thbit,which istheMSB,needstobestoredintheTX8bitintheUCR1register.Atthetransmittercoreliesthe TransmitterShiftRegister,morecommonlyknownastheTSR,whosedataisobtainedfromthe transmitdataregister,whichisknownastheTXRregister.Thedatatobetransmittedisloaded intothisTXRregisterbytheapplicationprogram.TheTSRregisterisnotwrittentowithnewdata untilthestopbitfromtheprevioustransmissionhasbeensentout.Assoonasthisstopbithasbeen transmitted,theTSRcanthenbeloadedwithnewdatafromtheTXRregister,ifitisavailable.It shouldbenotedthattheTSRregister,unlikemanyotherregisters,isnotdirectlymappedintothe DataMemoryareaandassuchisnotavailabletotheapplicationprogramfordirectread/write operations.AnactualtransmissionofdatawillnormallybeenabledwhentheTXENbitisset,but thedatawillnotbetransmitteduntiltheTXRregisterhasbeenloadedwithdataandthebaudrate generatorhasdefinedashiftclocksource.However,thetransmissioncanalsobeinitiatedbyfirst loadingdataintotheTXRregister,afterwhichtheTXENbitcanbeset.Whenatransmissionof databegins,theTSRisnormallyempty,inwhichcaseatransfertotheTXRregisterwillresultin animmediatetransfertotheTSR.IfduringatransmissiontheTXENbitiscleared,thetransmission willimmediatelyceaseandthetransmitterwillbereset.TheTXoutputpinwillthenreturntotheI/O orotherpin-sharedfunction. Transmitting Data WhentheUARTistransmittingdata,thedataisshiftedontheTXpinfromtheshiftregister,with theleastsignificantbitfirst.Inthetransmitmode,theTXRregisterformsabufferbetweenthe internalbusandthetransmittershiftregister.Itshouldbenotedthatif9-bitdataformathasbeen selected,thentheMSBwillbetakenfromtheTX8bitintheUCR1register.Thestepstoinitiatea datatransfercanbesummarizedasfollows: • MakethecorrectselectionoftheBNO,PRT,PRENandSTOPSbitstodefinetherequiredword length,paritytypeandnumberofstopbits. • SetuptheBRGregistertoselectthedesiredbaudrate. • SettheTXENbittoensurethattheTXpinisusedasaUARTtransmitterpin. • AccesstheUSRregisterandwritethedatathatistobetransmittedintotheTXRregister.Note thatthisstepwillcleartheTXIFbit. Thissequenceofeventscannowberepeatedtosendadditionaldata. ItshouldbenotedthatwhenTXIF=0,datawillbeinhibitedfrombeingwrittentotheTXRregister. ClearingtheTXIFflagisalwaysachievedusingthefollowingsoftwaresequence: • AUSRregisteraccess • ATXRregisterwriteexecution Theread-onlyTXIFflagissetbytheUARThardwareandifsetindicatesthattheTXRregisteris emptyandthatotherdatacannowbewrittenintotheTXRregisterwithoutoverwritingtheprevious data.IftheTEIEbitissetthentheTXIFflagwillgenerateaninterrupt. |
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