HT45FM2C datasheet(49/171 Pages) HOLTEK

49 / 171 page

Rev. 1.10

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Rev. 1.10

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HT45FM2C

Brushless DC Motor Flash Type 8-Bit MCU

HT45FM2C

Brushless DC Motor Flash Type 8-Bit MCU

Preliminar�

Reset and Initialisation

Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicecanbeset

tosomepredeterminedconditionirrespectiveofoutsideparameters.Themostimportantreset

conditionisafterpowerisfirstappliedtothemicrocontroller.Inthiscase,internalcircuitrywill

ensurethatthemicrocontroller,afterashortdelay,willbeinawelldefinedstateandreadyto

executethefirstprograminstruction.Afterthispower-onreset,certainimportantinternalregisters

willbesettodefinedstatesbeforetheprogramcommences.OneoftheseregistersistheProgram

Counter,whichwillberesettozeroforcingthemicrocontrollertobeginprogramexecutionfromthe

lowestProgramMemoryaddress.

AnothertypeofresetiswhentheWatchdogTimeroverflowsandresetsthemicrocontroller.All

typesofresetoperationsresultindifferentregisterconditionsbeingsetup.Anotherresetexistsinthe

formofaLowVoltageReset,LVR,wherethepowersupplyvoltagefallsbelowacertainthreshold.

Reset Functions

Therearefourwaysinwhichamicrocontrollerresetcanoccur,througheventsoccurringboth

internallyandexternally:

• Power-onReset

Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedto

themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirst

memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown

conditions.AlltheI/Oportandportcontrolregisterswillpowerupinahighconditionensuring

thatallpinswillbefirstsettoinputs.

VDD

Power-on Reset

SST Time-out

tRSTD

Note:tRSTDispower-ondelay,typicaltime=50ms

Power-on Reset Timing Chart

• LowVoltageReset–LVR

Thismicrocontrollercontainsalowvoltageresetcircuitinordertomonitorthesupplyvoltage

ofthisdevice,whichiscontrolledbyLVRCregister.Ifthesupplyvoltageofthedevicedrops

towithinarangeof0.9V~VLVRsuchasmightoccurwhenchangingthebattery,theLVRwill

automaticallyresetthedeviceinternallyandsettheLVRFintheCTRLregistertohigh.The

LVRincludesthefollowingspecifications:ForavalidLVRsignal,alowvoltage,i.e.,avoltage

intherangebetween0.9V~VLVRmustexistforgreaterthanthevaluetLVRspecifiedintheA.C.

characteristics.IfthelowvoltagestatedoesnotexceedtLVR,theLVRwillignoreitandwillnot

performaresetfunction.

LV R

In te r nal R es et

t RS TD + t SST

Note:tRSTDispower-ondelay,typicaltime=16.7ms

Low Voltage Reset Timing Chart

HT45FM2C Datenblatt(PDF) 49 Page - Holtek Semiconductor Inc

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