HT66F005 datasheet(31/109 Pages) HOLTEK

31 / 109 page

Rev. 1.30

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Rev. 1.30

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HT66F005/HT66F006

Cost-Effective A/D Flash MCU with EEPROM

HT66F005/HT66F006

Cost-Effective A/D Flash MCU with EEPROM

Oscillator

Variousoscillatoroptionsoffertheuserawiderangeoffunctionsaccordingtotheirvarious

applicationrequirements.Theflexiblefeaturesoftheoscillatorfunctionsensurethatthebest

optimisationcanbeachievedintermsofspeedandpowersaving.Oscillatorselectionsandoperation

areselectedthroughacombinationofconfigurationoptionsandregisters.

Oscillator Overview

Inadditiontobeingthesourceofthemainsystemclocktheoscillatorsalsoprovideclocksources

fortheWatchdogTimerandTimeBaseInterrupts.Externaloscillatorsrequiringsomeexternal

componentsaswellasfullyintegratedinternaloscillators,requiringnoexternalcomponents,

areprovidedtoformawiderangeofbothfastandslowsystemoscillators.Alloscillator

optionsareselectedthroughtheconfigurationoptions.Thehigherfrequencyoscillatorsprovide

higherperformancebutcarrywithitthedisadvantageofhigherpowerrequirements,whilethe

oppositeisofcoursetrueforthelowerfrequencyoscillators.Withthecapabilityofdynamically

switchingbetweenfastandslowsystemclock,thesedeviceshavetheflexibilitytooptimizethe

performance/powerratio,afeatureespeciallyimportantinpowersensitiveportableapplications.

Type

Name

Freq.

Pins

Exte�na� C�ysta�

HXT

400kHz~�0MHz

OSC1/OSC�

Inte�na� High S�eed RC

HIRC

4� 8� 1�MHz

—

Inte�na� Low S�eed RC

LIRC

3�kHz

—

Oscillator Types

System Clock Configurations

Therearethreemethodsofgeneratingthesystemclock,twohighspeedoscillatorsandonelow

speedoscillator.Thehighspeedoscillatorsaretheexternalcrystal/ceramicoscillatorandtheinternal

4MHz,8MHzor12MHzRCoscillator.Thelowspeedoscillatorisaninternal32kHzRCoscillator.

Selectingwhethertheloworhighspeedoscillatorisusedasthesystemoscillatorisimplemented

usingtheHLCLKbitandCKS2~CKS0bitsintheSMODregisterandasthesystemclockcanbe

dynamicallyselected.

Theactualsourceoscillatorusedforthehighspeedsystemclockischosenusingaconfiguration

option.TheOSC1andOSC2pinsareusedtoconnecttheexternalcomponentsfortheexternal

crystal.Theavailableselectionsforhighspeedandlowspeedoscillatorsaretherefore:HIRC+LIRC

orHXT+LIRC.

External Crystal/Ceramic Oscillator – HXT

TheExternalCrystal/CeramicSystemOscillatorisoneofthehighfrequencyoscillatorchoices,

whichisselectedviaconfigurationoption.Formostcrystaloscillatorconfigurations,thesimple

connectionofacrystalacrossOSC1andOSC2willcreatethenecessaryphaseshiftandfeedbackfor

oscillation,withoutrequiringexternalcapacitors.However,forsomecrystaltypesandfrequencies,

toensureoscillation,itmaybenecessarytoaddtwosmallvaluecapacitors,C1andC2.Usinga

ceramicresonatorwillusuallyrequiretwosmallvaluecapacitors,C1andC2,tobeconnectedas

shownforoscillationtooccur.ThevaluesofC1andC2shouldbeselectedinconsultationwiththe

crystalorresonatormanufacturer'sspecification.

Foroscillatorstabilityandtominimisetheeffectsofnoiseandcrosstalk,itisimportanttoensure

thatthecrystalandanyassociatedresistorsandcapacitorsalongwithinterconnectinglinesareall

locatedasclosetotheMCUaspossible.

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