HT45F12 datasheet(34/104 Pages) HOLTEK

34 / 104 page

Rev. 0.00

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Rev. 0.00

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HT45F12

8-Bit Flash MCU with Op Amps & Comparators

HT45F12

8-Bit Flash MCU with Op Amps & Comparators

Selectingwhethertheloworhighspeedoscillatorisusedasthesystemoscillatorisimplemented

usingtheHLCLKbitandLCKS2~LCKS0bitsintheSYSMODregisterandasthesystemclock

canbedynamicallyselected.Theactualsourceclockusedforeachofthehighspeedandlowspeed

oscillatorsischosenviaconfigurationoptions.Thefrequencyoftheslowspeedorhighspeed

systemclockisalsodeterminedusingtheHLCLKbitandLCKS2~LCKS0bitsintheSYSMOD

systemoscillators.Itisnotpossibletochooseano-oscillatorselectionforeitherthehighorlow

speedoscillator.

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.

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

0�F

8MHz

0�F

4MHz

0�F

1MHz

100�F

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

Crystal Recommended Capacitor Values

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