HT45F65 datasheet(46/231 Pages) HOLTEK

46 / 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

External RC Oscillator – ERC (HT45F66/HT45F67)

UsingtheERCoscillatoronlyrequiresthataresistor,withavaluebetween56kΩand2.4MΩ,

isconnectedbetweenOSC1andVDD,andacapacitorisconnectedbetweenOSC1andground,

providingalowcostoscillatorconfiguration.Itisonlytheexternalresistorthatdeterminesthe

oscillationfrequency;theexternalcapacitorhasnoinfluenceoverthefrequencyandisconnected

forstabilitypurposesonly.Devicetrimmingduringthemanufacturingprocessandtheinclusion

ofinternalfrequencycompensationcircuitsareusedtoensurethattheinfluenceofthepower

supplyvoltage,temperatureandprocessvariationsontheoscillationfrequencyareminimised.Asa

resistance/frequencyreferencepoint,itcanbenotedthatwithanexternal120kΩresistorconnected

andwitha5Vvoltagepowersupplyandtemperatureof25°Cdegrees,theoscillatorwillhavea

frequencyof8MHzwithinatoleranceof2%.HereonlytheOSC1pinisused,whichissharedwith

I/OpinPC1,leavingpinPC2freeforuseasanormalI/Opin.

Foroscillatorstabilityandtominimisetheeffectsofnoiseandcrosstalk,itisimportanttolocatethe

capacitorandresistorasclosetotheMCUaspossible.

OSC1

OSC2

I/O

ROSC

20pF

VDD

External RC Oscillator – ERC

Internal RC Oscillator – HIRC

TheinternalRCoscillatorisafullyintegratedsystemoscillatorrequiringnoexternalcomponents.

TheinternalRCoscillatorhasthreefixedfrequenciesofeither4MHz,8MHzor12MHz.Device

trimmingduringthemanufacturingprocessandtheinclusionofinternalfrequencycompensation

circuitsareusedtoensurethattheinfluenceofthepowersupplyvoltage,temperatureandprocess

variationsontheoscillationfrequencyareminimised.Asaresult,atapowersupplyofeither3V

or5Vandatatemperatureof25°Cdegrees,thefixedoscillationfrequencyof4MHz,8MHzor

12MHzwillhaveatolerancewithin1%.Notethatifthisinternalsystemclockoptionisselected,as

itrequiresnoexternalpinsforitsoperation,I/OpinsarefreeforuseasnormalI/Opins.

External 32.768kHz Crystal Oscillator – LXT

TheExternal32.768kHzCrystalSystemOscillatorisoneofthelowfrequencyoscillatorchoices,

whichisselectedviaconfigurationoption.Thisclocksourcehasafixedfrequencyof32.768kHz

andrequiresa32.768kHzcrystaltobeconnectedbetweenpinsXT1andXT2.Theexternalresistor

andcapacitorcomponentsconnectedtothe32.768kHzcrystalarenecessarytoprovideoscillation.

Forapplicationswhereprecisefrequenciesareessential,thesecomponentsmayberequiredto

providefrequencycompensationduetodifferentcrystalmanufacturingtolerances.Duringpower-up

thereisatimedelayassociatedwiththeLXToscillatorwaitingforittostart-up.

WhenthemicrocontrollerenterstheSLEEPorIDLEMode,thesystemclockisswitchedofftostop

microcontrolleractivityandtoconservepower.However,inmanymicrocontrollerapplicationsit

maybenecessarytokeeptheinternaltimersoperationalevenwhenthemicrocontrollerisinthe

SLEEPorIDLEMode.Todothis,anotherclock,independentofthesystemclock,mustbeprovided.

However,forsomecrystals,toensureoscillationandaccuratefrequencygeneration,itisnecessary

toaddtwosmallvalueexternalcapacitors,C1andC2.TheexactvaluesofC1andC2should

beselectedinconsultationwiththecrystalorresonatormanufacturerspecification.Theexternal

parallelfeedbackresistor,RP,isrequired.

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