Holtek HT66F30 - Oscillators; Oscillator Overview; System Clock Configurations

Rev. 2.50 50 June 22, 2017 Rev. 2.50 51 June 22, 2017
HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
Oscillators
Variousoscillatoroptionsoffertheuserawiderangeoffunctionsaccordingtotheirvarious
applicationrequirements.Theflexible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registers.
Oscillator Overview
Inadditiontobeingthesourceofthemainsystemclocktheoscillatorsalsoprovideclocksources
fortheWatchdog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theconfiguration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 Freq. Pins
External Crystal HXT 400kHz~20MHz
OSC1/OSC2
External RC ERC 8MHz OSC1
Internal High Speed RC HIRC 4, 8 or 12MHz —
External Low Speed Crystal LXT
32.768kHz XT1/XT2
Internal Low Speed RC LIRC 32kHz —
Oscillator Types
System Clock Congurations
Therearevemethodsofgeneratingthesystemclock,threehighspeedoscillatorsandtwolow
speedoscillators.Thehighspeedoscillatorsaretheexternalcrystal/ceramicoscillator,external
RCnetworkoscillatorandtheinternal4MHz,8MHzor12MHzRCoscillator.Thetwolowspeed
oscillatorsaretheinternal32kHzRCoscillatorandtheexternal32.768kHzcrystaloscillator.
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speed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.Itis
notpossibletochooseano-oscillatorselectionforeitherthehighorlowspeedoscillator.