HT67F488 datasheet(38/171 Pages) HOLTEK

38 / 171 page

Rev. 1.60

�ove��e� �� 016

HT67F488/HT67F489

TinyPowerTM A/D Flash MCU with LCD & EEPROM

External Crystal/Ceramic Oscillator – HXT

TheExternalCrystal/CeramicSystemOscillatorisoneofthehighfrequencyoscillatorchoices,

whichisselectedviaconfigurationoption.Formostcrystaloscillatorconfigurations,thesimple

connectionofacrystalacrossOSC1andOSC2willcreatethenecessaryphaseshiftandfeedbackfor

oscillation,withoutrequiringexternalcapacitors.However,forsomecrystaltypesandfrequencies,

toensureoscillation,itmaybenecessarytoaddtwosmallvaluecapacitors,C1andC2.Usinga

ceramicresonatorwillusuallyrequiretwosmallvaluecapacitors,C1andC2,tobeconnectedas

shownforoscillationtooccur.ThevaluesofC1andC2shouldbeselectedinconsultationwiththe

crystalorresonatormanufacturer'sspecification.Anadditionalconfigurationoptionmustbesetup

toconfigurethedeviceaccordingtowhethertheoscillatorfrequencyishigh,definedasequaltoor

above1MHz,orlow,whichisdefinedasbelow1MHz.

Foroscillatorstabilityandtominimisetheeffectsofnoiseandcrosstalk,itisimportanttoensure

thatthecrystalandanyassociatedresistorsandcapacitorsalongwithinterconnectinglinesareall

locatedasclosetotheMCUaspossible.

OS C1

OS C2

To i nt er nal

ci rc ui ts

In te rn al

O sci lla to r

Ci rc ui t

No te :1 . Rp i s nor ma lly not r equi r ed. C 1 and C2 a re r equ ir ed.

2. A lt hough not s how n OS C1 /O SC 2 pi ns h av e a pa ra si ti c

c apac it an ce o f a r ound 7pF .

Crystal/Resonator Oscillator – HXT

Crystal Oscillator C1 and C2 Values

Crystal Frequency

1�MHz

0pF

8MHz

0pF

4MHz

0pF

1MHz

100pF

455kHz (see �ote�)

100pF

�ote: 1. C1 and C� values a�e fo� guidance only.

2. XTAL mode configuration option: 455kHz.

Crystal Recommended Capacitor Values

Internal RC Oscillator – HIRC

TheinternalRCoscillatorisafullyintegratedsystemoscillatorrequiringnoexternalcomponents.

The internal RC oscillator has a fixed frequency of 8MHz. Device trimming during the

manufacturingprocessandtheinclusionofinternalfrequencycompensationcircuitsareusedto

ensurethattheinfluenceofthepowersupplyvoltage,temperatureandprocessvariationsonthe

oscillationfrequencyareminimised.Notethatifthisinternalsystemclockoptionisselected,asit

requiresnoexternalpinsforitsoperation,I/OpinsarefreeforuseasnormalI/Opins.

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