HT69F240 datasheet(34/172 Pages) HOLTEK

34 / 172 page

Rev. 1.20

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Rev. 1.20

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HT69F240

I/O 8-Bit Flash MCU with LED/LCD Driver

HT69F240

I/O 8-Bit Flash MCU with LED/LCD Driver

External 32.768kHz Crystal Oscillator – LXT

TheExternal32.768kHzCrystalSystemOscillatorisoneofthelowfrequencyoscillatorchoices,

whichisselectedviaconfigurationoption.Thisclocksourcehasafixedfrequencyof32.768kHz

andrequiresa32.768kHzcrystaltobeconnectedbetweenpinsXT1andXT2.Theexternalresistor

andcapacitorcomponentsconnectedtothe32.768kHzcrystalarenecessarytoprovideoscillation.

Forapplicationswhereprecisefrequenciesareessential,thesecomponentsmayberequiredto

providefrequencycompensationduetodifferentcrystalmanufacturingtolerances.Duringpower-up

thereisatimedelayassociatedwiththeLXToscillatorwaitingforittostart-up.

WhenthemicrocontrollerenterstheSLEEPorIDLEMode,thesystemclockisswitchedofftostop

microcontrolleractivityandtoconservepower.However,inmanymicrocontrollerapplicationsit

maybenecessarytokeeptheinternaltimersoperationalevenwhenthemicrocontrollerisinthe

SLEEPorIDLEMode.Todothis,anotherclock,independentofthesystemclock,mustbeprovided.

However,forsomecrystals,toensureoscillationandaccuratefrequencygeneration,itisnecessary

toaddtwosmallvalueexternalcapacitors,C1andC2.TheexactvaluesofC1andC2shouldbe

selectedinconsultationwiththecrystalorresonatormanufacturer'sspecification.Theexternal

parallelfeedbackresistor,Rp,isrequired.

SomeconfigurationoptionsdetermineiftheXT1/XT2pinsareusedfortheLXToscillatororasI/O

pins.

• IftheLXToscillatorisnotusedforanyclocksource,theXT1/XT2pinscanbeusedas

normalI/Opins.

• IftheLXToscillatorisusedforanyclocksource,the32.768kHzcrystalshouldbeconnectedto

theXT1/XT2pins.

Foroscillatorstabilityandtominimisetheeffectsofnoiseandcrosstalk,itisimportanttoensure

thatthecrystalandanyassociatedresistorsandcapacitorsalongwithinterconnectinglinesareall

locatedasclosetotheMCUaspossible.

To i nt er na l

ci rc ui ts

In te rn al

O sc illa to r

Ci rc ui t

No te :1 . Rp , C1 a nd C2 a re r e qui re d.

2. A lt hough n ot s ho wn p in s ha ve a p ar as it ic c apac it anc e

o f ar ound 7pF .

In te r nal R C

Os c illa to r

32 .7 68 kH z

XT 1

XT 2

External LXT Oscillator

LXT Oscillator C1 and C2 Values

Crystal Frequency

32.768kHz

10pF

Note:1. C1 and C2 values a�e fo� guidan�e only.

2. RP=��~10MΩ is recommended.

32.768kHz Crystal Recommended Capacitor Values

HT69F240 Datasheet(PDF) 34 Page - Holtek Semiconductor Inc

HT69F240 Datasheet(HTML) 34 Page - Holtek Semiconductor Inc

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