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HT45R4U Folha de dados(PDF) 37 Page - Holtek Semiconductor Inc |
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HT45R4U Folha de dados(HTML) 37 Page - Holtek Semiconductor Inc |
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37 / 105 page  Rev. 1.10 36 �a��� 1�� �01� Rev. 1.10 37 �a��� 1�� �01� HT45R4U TinyPowerTM A/D Type e-Banking ASSP OTP MCU with LCD LCD Driver Output ThenatureofLiquidCrystalDisplaysrequirethatonlyACvoltagescanbeappliedtotheirpixels astheapplicationofDCvoltagestoLCDpixelsmaycausepermanentdamage.Forthisreasonthe relativecontrastofanLCDdisplayiscontrolledbytheactualRMSvoltageappliedtoeachpixel, whichisequaltotheRMSvalueofthevoltageontheCOMpinminusthevoltageappliedtothe SEGpin.ThisdifferentialRMSvoltagemustbegreaterthantheLCDsaturationvoltageforthe pixeltobeonandlessthanthethresholdvoltageforthepixeltobeoff.Therequirementtolimitthe DCvoltagetozeroandtocontrolasmanypixelsaspossiblewithaminimumnumberofconnections requiresthatbothatimeandamplitudesignalisgeneratedandappliedtotheapplicationLCD. ThesetimeandamplitudevaryingsignalsareautomaticallygeneratedbytheLCDdrivercircuitsin themicrocontroller.Whatisknownasthedutydeterminesthenumberofcommonlinesused,which arealsoknownasbackplanesorCOMs.Theduty,whichhasavalueof1/4andwhichequatesto aCOMnumberof4,etc,thereforedefinesthenumberoftimedivisionswithineachLCDsignal frame.Twotypesofsignalgenerationarealsoprovided,knownasTypeAandTypeB,therequired typeisselectedviatheTYPEbitintheLCDCTRLregister.TypeBofferslowerfrequencysignals, howeverlowerfrequenciesmayintroduceflickeringandinfluencedisplayclarity. LCD Voltage Source and Biasing ThetimeandamplitudevaryingsignalsgeneratedbytheLCDDriverfunctionrequirethegeneration ofseveralvoltagelevelsfortheiroperation.ThebiasvoltagetypeisCtype1/3biasforLCDdisplay inthisdevice.TheCtypebiasingenablesaninternalchargepumpwhosemultiplierratiocanbe selectedusinganadditionalconfigurationoption. ForCtypebiasinganexternalLCDvoltagesourcemustalsobesuppliedonpinPLCDtogenerate theinternalbiasingvoltages.TheCtypebiasingschemeusesaninternalchargepumpcircuit,which inthecaseofthe1/3biasselectioncangeneratevoltageshigherthanwhatissuppliedonPLCDpin. Thisfeatureisusefulinapplicationswherethemicrocontrollersupplyvoltageislessthanthesupply voltagerequiredbytheLCD.Anadditionalchargepumpcapacitormustalsobeconnectedbetween pinsC1andC2togeneratethenecessaryvoltagelevels. FortheCtypemode1selection,fourvoltagelevelsVSS,VA,VBandVCareutilised.ThevoltageVAis generatedinternallyandhasavalueofVPLCD×3/2.ThevoltageVBwillhaveavalueequaltoVPLCDand VCwillhaveavalueequaltoVPLCD×1/2.TheconnectiontotheVMAXpindependsuponthevoltage thatisappliedtoPLCDandthedetailsareshowninthetable Voltage Level VMAX Connection VDD > VPLCD × 3/� Conne�t V�AX to VDD Ot�e�wise Conne�t V�AX to V1 C Type 1/3 Biasing VMAX Connection (for mode 1) FortheCtypemode2selection,fourvoltagelevelsVSS,VA,VBandVCareutilised.ThevoltageVA isgeneratedinternallyandhasavalueofV1.ThevoltageVBwillhaveavalueequaltoV1×2/3and VCwillhaveavalueequaltoV1×1/3.TheVMAXpinmustconnectedtotheV1pin. |
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