HT67F488 datasheet(37/171 Pages) HOLTEK

37 / 171 page

Rev. 1.60

�ove��e� �� 016

HT67F488/HT67F489

TinyPowerTM A/D Flash MCU with LCD & EEPROM

Oscillators

Variousoscillatoroptionsoffertheuserawiderangeoffunctionsaccordingtotheirvarious

applicationrequirements.Theflexiblefeaturesoftheoscillatorfunctionsensurethatthebest

optimisationcanbeachievedintermsofspeedandpowersaving.Oscillatorselectionsandoperation

areselectedthroughregisters.

Oscillator Overview

Inadditiontobeingthesourceofthemainsystemclocktheoscillatorsalsoprovideclocksources

fortheWatchdogTimerandTimeBaseInterrupts.Externaloscillatorsrequiringsomeexternal

componentsaswellasfullyintegratedinternaloscillators,requiringnoexternalcomponents,are

providedtoformawiderangeofbothfastandslowsystemoscillators.Thehigherfrequency

oscillatorsprovidehigherperformancebutcarrywithitthedisadvantageofhigherpower

requirements,whiletheoppositeisofcoursetrueforthelowerfrequencyoscillators.Withthe

capabilityofdynamicallyswitchingbetweenfastandslowsystemclock,thedevicehasthe

flexibilitytooptimizetheperformance/powerratio,afeatureespeciallyimportantinpowersensitive

portableapplications.

Type

Name

Freq.

Pins

Inte�nal High Speed RC

HIRC

8MHz

—

Exte�nal High speed C�ystal

HXT

400kHz~16MHz

OSC1/OSC�

Inte�nal Low Speed RC

LIRC

3�kHz

—

Exte�nal Low Speed C�ystal

LXT

3�.768kHz

XT1/XT�

Oscillator Types

System Clock Configurations

Therearefourmethodsofgeneratingthesystemclock,twohighspeedoscillatorsandtwolowspeed

oscillators.Thehighspeedoscillatoraretheinternal8MHzRCoscillator-HIRCandtheexternal

crystal/ceramicoscillator-HXT.Thetwolowspeedoscillatorsaretheinternal32kHzRCoscillator

-LIRCandtheexternal32.768kHzcrystaloscillator-LXT.Selectingwhethertheloworhighspeed

oscillatorisusedasthesystemoscillatorisimplementedusingtheHLCLKbitandCKS2~CKS0

bitsintheSMODregisterandasthesystemclockcanbedynamicallyselected.Notethattwo

oscillatorselectionsmustbemadenamelyonehighspeedandonelowspeedsystemoscillators.Itis

notpossibletochooseano-oscillatorselectionforeitherthehighorlowspeedoscillator.

LI RC

Hi gh S peed O sc illa to rs

Lo w Sp eed Os ci ll at or s

f H

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 sca le r

f SYS

HL CL K,

CK S2 ~C KS 0 bi ts

LX T

FS UB C

FS UB 6~ FS UB 0 bi ts

f SU B

HI RC

HX T

Co nf ig ur at io n

Op ti on

System Clock Configurations

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