HT45F65 datasheet(198/231 Pages) HOLTEK

198 / 231 page

Rev. 1.60

198

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Rev. 1.60

199

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HT45F65/HT45F66/HT45F67

Glucose Meter 8-Bit Flash MCU

Theread-onlyTXIFflagissetbytheUARThardwareandifsetindicatesthattheTXRregisteris

emptyandthatotherdatacannowbewrittenintotheTXRregisterwithoutoverwritingtheprevious

data.IftheTEIEbitisset,thentheTXIFflagwillgenerateaninterrupt.Duringadatatransmission,

awriteinstructiontotheTXRregisterwillplacethedataintotheTXRregister,whichwillbe

copiedtotheshiftregisterattheendofthepresenttransmission.Whenthereisnodatatransmission

inprogress,awriteinstructiontotheTXRregisterwillplacethedatadirectlyintotheshiftregister,

resultinginthecommencementofdatatransmission,andtheTXIFbitbeingimmediatelyset.When

aframetransmissioniscomplete,whichhappensafterstopbitsaresentorafterthebreakframe,the

TIDLEbitwillbeset.TocleartheTIDLEbitthefollowingsoftwaresequenceisused:

1.AUSRregisteraccess

2.ATXRregisterwriteexecution

NotethatboththeTXIFandTIDLEbitsareclearedbythesamesoftwaresequence.

Transmitting Break

IftheTXBRKbitisset,thenthebreakcharacterswillbesentonthenexttransmission.Break

charactertransmissionconsistsofastartbit,followedby13xN“0”bits,whereN=1,2,etc.ifa

breakcharacteristobetransmitted,thentheTXBRKbitmustbefirstsetbytheapplicationprogram

andthenclearedtogeneratethestopbits.Transmittingabreakcharacterwillnotgenerateatransmit

interrupt.Notethatabreakconditionlengthisatleast13bitslong.IftheTXBRKbitiscontinually

keptatalogichighlevel,thenthetransmittercircuitrywilltransmitcontinuousbreakcharacters.

AftertheapplicationprogramhasclearedtheTXBRKbit,thetransmitterwillfinishtransmittingthe

lastbreakcharacterandsubsequentlysendoutoneortwostopbits.Theautomaticlogichighatthe

endofthelastbreakcharacterwillensurethatthestartbitofthenextframeisrecognized.

UART Receiver

TheUARTiscapableofreceivingwordlengthsofeither8or9bitscanbeselectedbyprogramming

theBNObitintheUCR1register.WhenBNObitisset,thewordlengthwillbesetto9bits.In

thiscasethe9thbit,whichistheMSB,willbestoredintheRX8bitintheUCR1register.Atthe

receivercoreliestheReceiverShiftRegistermorecommonlyknownastheRSR.Thedatawhich

isreceivedontheRXexternalinputpinissenttothedatarecoveryblock.Thedatarecoveryblock

operatingspeedis16timesthatofthebaudrate,whilethemainreceiveserialshifteroperatesatthe

baudrate.AftertheRXpinissampledforthestopbit,thereceiveddatainRSRistransferredtothe

receivedataregister,iftheregisterisempty.ThedatawhichisreceivedontheexternalRXinputpin

issampledthreetimesbyamajoritydetectcircuittodeterminethelogiclevelthathasbeenplaced

ontotheRXpin.ItshouldbenotedthattheRSRregister,unlikemanyotherregisters,isnotdirectly

mappedintotheDataMemoryareaandassuchisnotavailabletotheapplicationprogramfordirect

read/writeoperations.

Receiving Data

WhentheUARTreceiverisreceivingdata,thedataisseriallyshiftedinontheexternalRXinput

pintotheshiftregister,withtheleastsignificantbitLSBfirst.TheRXRregisterisafourbytedeep

FIFOdatabuffer,wherefourbytescanbeheldintheFIFOwhilethe5thbytecancontinuetobe

received.NotethattheapplicationprogrammustensurethatthedataisreadfromRXRbeforethe

5thbytehasbeencompletelyshiftedin,otherwisethe5thbytewillbediscardedandanoverrun

errorOERRwillbesubsequentlyindicated.Thestepstoinitiateadatatransfercanbesummarized

asfollows:

• MakethecorrectselectionoftheBNO,PRT,PRENandSTOPSbitstodefinetherequiredword

length,paritytypeandnumberofstopbits.

HT45F65 Datasheet(PDF) 198 Page - Holtek Semiconductor Inc

HT45F65 Datasheet(HTML) 198 Page - Holtek Semiconductor Inc

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