HT66F25D datasheet(36/177 Pages) HOLTEK

36 / 177 page

Rev. 1.00

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Rev. 1.00

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A/D Flash Type 8-bit MCU with EEPROM

HT66F24D/HT66F25D

Oscillator

Variousoscillatoroptionsoffertheuserawiderangeoffunctionsaccordingtotheirvarious

applicationrequirements.Theflexiblefeaturesoftheoscillatorfunctionsensurethatthebest

optimisationcanbeachievedintermsofspeedandpowersaving.Oscillatorselectionsandoperation

areselectedthroughacombinationofconfigurationoptionsandregisters.

Oscillator Overview

Inadditiontobeingthesourceofthemainsystemclocktheoscillatorsalsoprovideclocksources

fortheWatchdogTimerandTimeBaseInterrupts.Externaloscillatorsrequiringsomeexternal

componentsaswellasfullyintegratedinternaloscillators,requiringnoexternalcomponents,

areprovidedtoformawiderangeofbothfastandslowsystemoscillators.Alloscillatoroptions

areselectedthroughtheconfigurationoptions.Thehigherfrequencyoscillatorsprovidehigher

performancebutcarrywithitthedisadvantageofhigherpowerrequirements,whiletheopposite

isofcoursetrueforthelowerfrequencyoscillators.Withthecapabilityofdynamicallyswitching

betweenfastandslowsystemclock,thedevicehastheflexibilitytooptimizetheperformance/power

ratio,afeatureespeciallyimportantinpowersensitiveportableapplications.

Type

Name

Freq.

Pins

Externa� High Speed Cr�sta�

HXT

400kHz~1�MHz

OSC1/OSC�

Interna� High Speed RC

HIRC

4� 8 or 1�MHz

—

Externa� Low Speed Cr�sta�

LXT

3�.7�8 kHz

XT1/XT�

Interna� Low Speed RC

LIRC

3�kHz

—

Oscillator Types

System Clock Configurations

Therearefoursystemoscillators,twohighspeedandtwolowspeedoscillators.Thehighspeed

oscillatorsaretheexternalcrystal/ceramicoscillator–HXTandtheinternalRCoscillator-HIRC.

Thelowspeedoscillatorsaretheinternal32kHzoscillator–LIRCandtheexternal32.768kHz

crystaloscillator–LXT.Selectingwhethertheloworhighspeedoscillatorisusedasthesystem

oscillatorisimplementedusingtheHLCLKbitandCKS2~CKS0bitsintheSMODregisterandas

thesystemclockcanbedynamicallyselected.

Theactualsourceclockusedforeachofthehighspeedandlowspeedoscillatorsischosen

viaconfigurationoptions.Thefrequencyoftheslowspeedorhighspeedsystemclockisalso

determinedusingtheHLCLKbitandCKS2~CKS0bitsintheSMODregister.Notethattwo

oscillatorselectionsmustbemadenamelyonehighspeedandonelowspeedsystemoscillators.Itis

notpossibletochooseano-oscillatorselectionforeitherthehighorlowspeedoscillator.

HT66F25D Datasheet(PDF) 36 Page - Holtek Semiconductor Inc

HT66F25D Datasheet(HTML) 36 Page - Holtek Semiconductor Inc

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