HT45F3W datasheet(65/167 Pages) HOLTEK

65 / 167 page

Rev. 1.50

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HT45F3W

R-Type Blood Pressure Meter Flash MCU

HT45F3W

R-Type Blood Pressure Meter Flash MCU

Reset and Initialisation

Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicecanbeset

tosomepredeterminedconditionirrespectiveofoutsideparameters.Themostimportantreset

conditionisafterpowerisfirstappliedtothemicrocontroller.Inthiscase,internalcircuitrywill

ensurethatthemicrocontroller,afterashortdelay,willbeinawelldefinedstateandreadyto

executethefirstprograminstruction.Afterthispower-onreset,certainimportantinternalregisters

willbesettodefinedstatesbeforetheprogramcommences.OneoftheseregistersistheProgram

Counter,whichwillberesettozeroforcingthemicrocontrollertobeginprogramexecutionfromthe

lowestProgramMemoryaddress.

AnothertypeofresetiswhentheWatchdogTimeroverflowsandresets.Alltypesofresetoperations

resultindifferentregisterconditionsbeingsetup.AnotherresetexistsintheformofaLowVoltage

Reset,LVR,whereafullreset,isimplementedinsituationswherethepowersupplyvoltagefalls

belowacertainthreshold.

Reset Functions

Thereareseveralwaysinwhicharesetcanoccur,eachofwhichwillbedescribedasfollows.

Power-on Reset

Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedto

themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirst

memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown

conditions.AlltheI/Oportandportcontrolregisterswillpowerupinahighconditionensuringthat

allI/Oportswillbefirstsettoinputs.

VDD

Powe�-on Reset

SST Ti�e-out

tRSTD

Power-On Reset Timing Chart

Low Voltage Reset – LVR

Themicrocontrollercontainsalowvoltageresetcircuitinordertomonitorthesupplyvoltageof

thedevice.TheLVRfunctionisalwaysenabledwithaspecificLVRvoltage,VLVR.Ifthesupply

voltageofthedevicedropstowithinarangeof0.9V~VLVRsuchasmightoccurwhenchanging

thebattery,theLVRwillautomaticallyresetthedeviceinternally.TheLVRincludesthefollowing

specifications:ForavalidLVRsignal,alowvoltage,i.e.,avoltageintherangebetween0.9V~VLVR

mustexistforgreaterthanthevaluetLVRspecifiedintheLVRElectricalCharacteristics.Ifthelow

voltagestatedoesnotexceedtLVR,theLVRwillignoreitandwillnotperformaresetfunction.The

actualVLVRvaluecanbeselectedbytheLVS7~LVS0bitsintheLVRCregister.IftheLVS7~LVS0

bitsarechangedtosomecertainvaluesbytheenvironmentalnoiseorsoftwaresetting,theLVRwill

resetthedeviceafter2~3LIRCclockcycles.Whenthishappens,theLRFbitintheSMOD1register

willbesetto1.Afterpowerontheregisterwillhavethevalueof01010101B.NotethattheLVR

functionwillbeautomaticallydisabledwhenthedeviceentersthepowerdownmode.

LV R

In te r nal R es et

t RS TD + t SST

Low Voltage Reset Timing Chart

HT45F3W Datasheet(PDF) 65 Page - Holtek Semiconductor Inc

HT45F3W Datasheet(HTML) 65 Page - Holtek Semiconductor Inc

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