HT45F3W datasheet(48/167 Pages) HOLTEK

48 / 167 page

Rev. 1.50

De�e��e� 01� �01�

Rev. 1.50

De�e��e� 01� �01�

HT45F3W

R-Type Blood Pressure Meter Flash MCU

HT45F3W

R-Type Blood Pressure Meter Flash MCU

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,inmanymicrocontrollerapplications

itmaybenecessarytokeeptheinternaltimersoperationalevenwhenthemicrocontrollerisin

theSLEEPorIDLEMode.Todothis,anotherclock,independentofthesystemclock,mustbe

provided.

However,forsomecrystals,toensureoscillationandaccuratefrequencygeneration,itisnecessary

toaddtwosmallvalueexternalcapacitors,C1andC2.TheexactvaluesofC1andC2should

beselectedinconsultationwiththecrystalorresonatormanufacturerspecification.Theexternal

parallelfeedbackresistor,RP,isrequired.

SomeconfigurationoptionsdetermineiftheXT1/XT2pinsareusedfortheLXToscillatororasI/O

pins.

• IftheLXToscillatorisnotusedforanyclocksource,theXT1/XT2pinscanbeusedasnormalI/O

pins.

• IftheLXToscillatorisusedforanyclocksource,the32.768kHzcrystalshouldbeconnectedto

theXT1/XT2pins.

Foroscillatorstabilityandtominimisetheeffectsofnoiseandcrosstalk,itisimportanttoensure

thatthecrystalandanyassociatedresistorsandcapacitorsalongwithinterconnectinglinesareall

locatedasclosetotheMCUaspossible.

To i nt er nal

ci rc ui ts

In te rn al

O sci ll at or

Ci rc ui t

No te :1 . Rp , C 1 and C 2 ar e re qui r ed.

2. A lt hough not s how n pi ns h av e a

par as it ic c apac it an ce o f ar ound 7pF .

In te r nal R C

O sc illa to r

32. 76 8

kH z

XT 1

XT 2

External LXT Oscillator

LXT Oscillator C1 and C2 Values

Crystal Frequency

3�.7�8kHz

10pF

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

�. RP=5M~10MΩ is recommended.

32.768kHz Crystal Recommended Capacitor Values

HT45F3W Datasheet(PDF) 48 Page - Holtek Semiconductor Inc

HT45F3W Datasheet(HTML) 48 Page - Holtek Semiconductor Inc

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