Holtek HT66F002 - Internal RC Oscillator - HIRC; Internal 32 kHz Oscillator - LIRC; Operating Modes and System Clocks

Rev. 1.71 38 April 11, 2017 Rev. 1.71 39 April 11, 2017
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
Internal RC Oscillator – HIRC
TheinternalRCoscillatorisafullyintegratedsystemoscillatorrequiringnoexternalcomponents.
Theinternal RCoscillatorhasafixedfrequencyof8MHz.Devicetrimmingduringthe
manufacturingprocessandtheinclusionofinternalfrequencycompensationcircuitsareusedto
ensurethattheinuenceofthepowersupplyvoltage,temperatureandprocessvariationsonthe
oscillationfrequencyareminimised.Asaresult,atapowersupplyof5Vandattemperatureof25°C
degrees,thexedoscillationfrequencyoftheHIRCwillhaveatolerancewithin2%.
Internal 32kHz Oscillator – LIRC
Theinternal32kHzSystemOscillatoristhelowfrequencyoscillator.Itisafullyintegrated
RCoscillatorwithatypicalfrequencyof32kHzat5V,requiringnoexternalcomponentsforits
implementation.Devicetrimmingduringthemanufacturingprocessandtheinclusionofinternal
frequencycompensationcircuitsareusedtoensurethattheinuenceofthepowersupplyvoltage,
temperatureandprocessvariationsontheoscillationfrequencyareminimised.
Supplementary Oscillator
Thelowspeed oscillator, inadditiontoprovidingasystemclock sourceisalsousedtoprovide
aclocksourcetotwootherdevicefunctions.ThesearetheWatchdogTimerandtheTimeBase
Interrupts.
Operating Modes and System Clocks
Presentdayapplicationsrequirethattheirmicrocontrollershavehighperformancebutoftenstill
demandthattheyconsumeaslittlepoweraspossible,conictingrequirementsthatareespecially
trueinbatterypoweredportableapplications.Thefastclocksrequiredforhighperformancewill
bytheirnatureincreasecurrentconsumptionandofcoursevice-versa,lowerspeedclocksreduce
currentconsumption.AsHoltekhasprovidedthesedeviceswithbothhighandlowspeedclock
sourcesandthemeanstoswitchbetweenthemdynamically,theusercanoptimisetheoperationof
theirmicrocontrollertoachievethebestperformance/powerratio.
System Clocks
ThesedeviceshavetwodifferentclocksourcesforboththeCPUandperipheralfunctionoperation.
Byprovidingtheuserwithclockoptionsusingregisterprogramming,aclocksystemcanbe
conguredtoobtainmaximumapplicationperformance.
Themainsystemclock,cancomefromeitherahighfrequency,f
H
,oralowfrequency,f
L
,andis
selectedusingtheHLCLKbitandCKS2~CKS0bitsintheSMODregister.Thehighspeedsystem
clockcanbesourcedfromHIRCoscillator.Thelowspeedsystemclocksourcecanbesourcedfrom
theinternalclockf
L
.Theotherchoice,whichisadividedversionofthehighspeedsystemoscillator
hasarangeoff
H
/2~f
H
/64.
Thereisoneadditionalinternalclockfortheperipheralcircuits,theTimeBaseclock,f
TBC
.f
TBC
is
sourcedfromtheLIRCoscillators.Thef
TBC
clockisusedasasourcefortheTimeBaseinterrupt
functionsandfortheTMs.