HT67F488 datasheet(41/171 Pages) HOLTEK

41 / 171 page

Rev. 1.60

�ove��e� �� 016

HT67F488/HT67F489

TinyPowerTM A/D Flash MCU with LCD & EEPROM

Operating Modes and System Clocks

Presentdayapplicationsrequirethattheirmicrocontrollershavehighperformancebutoftenstill

demandthattheyconsumeaslittlepoweraspossible,conflictingrequirementsthatareespecially

trueinbatterypoweredportableapplications.Thefastclocksrequiredforhighperformancewill

bytheirnatureincreasecurrentconsumptionandofcoursevice-versa,lowerspeedclocksreduce

currentconsumption.AsHoltekhasprovidedthesedeviceswithbothhighandlowspeedclock

sourcesandthemeanstoswitchbetweenthemdynamically,theusercanoptimisetheoperationof

theirmicrocontrollertoachievethebestperformance/powerratio.

System Clocks

ThedevicehasmanydifferentclocksourcesforboththeCPUandperipheralfunctionoperation.

Byprovidingtheuserwithawiderangeofclockoptionsusingconfigurationoptionsandregister

programming,aclocksystemcanbeconfiguredtoobtainmaximumapplicationperformance.

Themainsystemclock,cancomefromeitherahighfrequencyfHorlowfrequencyfSUBsource,

andisselectedusingtheHLCLKbitandCKS2~CKS0bitsintheSMODregister.Thehighspeed

systemclockcanbesourcedfromtheHIRC/HXToscillator.Thelowspeedsystemclocksource

canbesourcedfrominternalclockfSUB.IffSUBisselectedthenitcanbesourcedbyeithertheLXT

orLIRCoscillator,selectedbytheFSUB6~FSUB0bitsintheFSUBCregister.Theotherchoice,

whichisadividedversionofthehighspeedsystemoscillatorhasarangeoffH/2~fH/64.

Ti me B as e 0

WD T

LI RC

Lo w S peed O sci lla to rs

f H /6 4

f H /3 2

f H /1 6

f H /8

f H /4

f H /2

6- st age P re sc al er

f SYS

HL CL K,

CK S2 ~C KS 0 bi ts

Ti me B as e 1

LX T

FS UB C

FS UB 6~ FS UB 0 bi ts

f SU B

TB CK

f TB C

f SYS /4

f TB

sl eep

To p er ip he ra ls

Hi gh Sp e ed O sci lla to rs

f H

HI RC

HX T

Co nf i gur at io n

Op ti on

System Clock Configuration

Note:WhenthesystemclocksourcefSYSisswitchedtofSUBfromfH,thehighspeedoscillationwillstopto

conservethepower.ThusthereisnofH~fH/64forperipheralcircuittouse.

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