Holtek HT66F0175 - Oscillator; Oscillator Overview; System Clock Configurations

Rev. 1.50 40 August 28, 2017 Rev. 1.50 41 August 28, 2017
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
Oscillator
Variousoscillatortypesoffertheuserawiderangeoffunctionsaccordingtotheirvariousapplication
requirements.Theexiblefeaturesoftheoscillatorfunctionsensurethatthebestoptimisationcan
beachievedintermsofspeedandpowersaving.Oscillatorselectionsandoperationareselected
throughacombinationofcongurationoptionsandrelevantcontrolregisters.
Oscillator Overview
Inadditiontobeingthesourceofthemainsystemclocktheoscillatorsalsoprovideclocksources
fortheWatchdogTimerandTimeBaseInterrupts.Externaloscillatorsrequiringsomeexternal
componentsaswellasfullyintegratedinternaloscillators,requiringnoexternalcomponents,are
providedtoformawiderangeofbothfastandslowsystemoscillators.Alloscillatoroptionsare
selectedthroughcongurationoptions.Thehigherfrequencyoscillatorsprovidehigherperformance
butcarrywithitthedisadvantageofhigherpowerrequirements,whiletheoppositeisofcoursetrue
forthelowerfrequencyoscillators.Withthecapabilityofdynamicallyswitchingbetweenfastand
slowsystemclock,thedevicehastheexibilitytooptimizetheperformance/powerratio,afeature
especiallyimportantinpowersensitiveportableapplications.
Type Name Frequency Pins
High Speed External Crystal HXT 400 kHz~20 MHz OSC1/OSC2
High Speed Internal RC HIRC 8/12/16 MHz —
Low Speed External Crystal LXT 32.768 kHz XT1/XT2
Low Speed Internal RC LIRC 32 kHz —
Oscillator Types
System Clock Congurations
Therearefourmethodsofgeneratingthesystemclock,twohighspeedoscillatorsforalldevicesand
twolowspeedoscillators.Thehighspeedoscillatoristheexternalcrystal/ceramicoscillator,HXT,
andtheinternal8/12/16MHzRCoscillator,HIRC.Thetwolowspeedoscillatorsaretheinternal32
kHzRCoscillator,LIRC,andtheexternal32.768kHzcrystaloscillator,LXT.Selectingwhetherthe
loworhighspeedoscillatorisusedasthesystemoscillatorisimplementedusingtheHLCLKbit
andCKS2~CKS0bitsintheSMODregisterandasthesystemclockcanbedynamicallyselected.
Theactualsourceclockusedforeachofthehighandlowspeedoscillatorsischosenvia
configurationoptions.Thefrequencyoftheslowspeedorhighspeedsystemclockisalso
determinedusingtheHLCLKbitandCKS2~CKS0bitsintheSMODregister.Notethattwo
oscillatorselectionsmustbemadenamelyonehighspeedandonelowspeedsystemoscillators.