HT45F65 datasheet(208/231 Pages) HOLTEK

208 / 231 page

Rev. 1.60

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Rev. 1.60

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HT45F65/HT45F66/HT45F67

Glucose Meter 8-Bit Flash MCU

Clock Source

TheLCDclocksourceistheinternalclocksignal,fSUB,dividedby8,usinganinternaldivider

circuit.ThefSUBinternalclockissuppliedbyeithertheLIRCorLXToscillator,thechoiceofwhich

isdeterminedbyaconfigurationoption.ForproperLCDoperation,thisarrangementisprovidedto

generateanidealLCDclocksourcefrequencyof4kHz.

fSUB Clock Source

LCD Clock Frequency

LIRC

�kHz

LXT

�kHz

LCD Clock Source

LCD Driver Output

ThenumberofCOMandSEGoutputssuppliedbytheLCDdriver,aswellasitsdutyselections,is

dependentuponhowtheLCDcontrolbitsareprogrammed.

ThenatureofLiquidCrystalDisplaysrequirethatonlyACvoltagescanbeappliedtotheirpixels

astheapplicationofDCvoltagestoLCDpixelsmaycausepermanentdamage.Forthisreasonthe

relativecontrastofanLCDdisplayiscontrolledbytheactualRMSvoltageappliedtoeachpixel,

whichisequaltotheRMSvalueofthevoltageontheCOMpinminusthevoltageappliedtothe

SEGpin.ThisdifferentialRMSvoltagemustbegreaterthantheLCDsaturationvoltageforthe

pixeltobeonandlessthanthethresholdvoltageforthepixeltobeoff.

TherequirementtolimittheDCvoltagetozeroandtocontrolasmanypixelsaspossiblewith

aminimumnumberofconnections,requiresthatbothatimeandamplitudesignalisgenerated

andappliedtotheapplicationLCD.Thesetimeandamplitudevaryingsignalsareautomatically

generatedbytheLCDdrivercircuitsinthemicrocontroller.Whatisknownasthedutydetermines

thenumberofcommonlinesused,whicharealsoknownasbackplanesorCOMs.Theduty,which

ischosenbyacontrolbittohaveavalueof1/3andwhichequatestoaCOMnumberof3,therefore

definesthenumberoftimedivisionswithineachLCDsignalframe.Twotypesofsignalgeneration

arealsoprovided,knownasTypeAandTypeB,therequiredtypeisselectedviatheTYPEbitinthe

LCDCregister.TypeBofferslowerfrequencysignals,howeverlowerfrequenciesmayintroduce

flickeringandinfluencedisplayclarity.

LCD Waveform Timing Diagrams

The accompanying timing diagrams depict the display driver signals generated by the

microcontrollerforvariousvaluesofduty.Thehugerangeofvariouspermutationsonlypermitsa

fewtypestobedisplayedhere.

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