HT66F019 datasheet(52/175 Pages) HOLTEK

52 / 175 page

Rev. 1.00

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Rev. 1.00

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HT66F019

A/D Flash MCU with EEPROM

HT66F019

A/D Flash MCU with EEPROM

Reset and Initialisation

Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicecanbeset

tosomepredeterminedconditionirrespectiveofoutsideparameters.Themostimportantreset

conditionisafterpowerisfirstappliedtothemicrocontroller.Inthiscase,internalcircuitrywill

ensurethatthemicrocontroller,afterashortdelay,willbeinawell-definedstateandreadyto

executethefirstprograminstruction.Afterthispower-onreset,certainimportantinternalregisters

willbesettodefinedstatesbeforetheprogramcommences.OneoftheseregistersistheProgram

Counter,whichwillberesettozeroforcingthemicrocontrollertobeginprogramexecutionfromthe

lowestProgramMemoryaddress.

AnothertypeofresetiswhentheWatchdogTimeroverflowsandresetsthemicrocontroller.All

typesofresetoperationsresultindifferentregisterconditionsbeingsetup.Anotherresetexistsinthe

formofaLowVoltageReset,LVR,whereafullresetisimplementedinsituationswherethepower

supplyvoltagefallsbelowacertainthreshold.

Reset Functions

Thereareseveralwaysinwhichamicrocontrollerresetcanoccur,througheventsoccurring

internally.

Power-on Reset

Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedto

themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirst

memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown

conditions.AlltheI/Oportsandportcontrolregisterswillpowerupinahighconditionensuring

thatallI/Oportswillbefirstsettoinputs.

VDD

Powe�-on Reset

SST Ti�e-out

tRSTD

Power-On Reset Timing Chart

Low Voltage Reset – LVR

Themicrocontrollercontainsalowvoltageresetcircuitinordertomonitorthesupplyvoltageofthe

device.TheLVRfunctionisalwaysenabledwithaspecificLVRvoltageVLVR.Ifthesupplyvoltage

ofthedevicedropstowithinarangeof0.9V~VLVRsuchasmightoccurwhenchangingthebattery,

theLVRwillautomaticallyresetthedeviceinternallyandtheLVRFbitintheCTRLregisterwill

alsobesethigh.ForavalidLVRsignal,alowsupplyvoltage,i.e.,avoltageintherangebetween

0.9V~VLVRmustexistforatimegreaterthanthatspecifiedbytLVRintheLVD/LVRElectrical

Characteristics.Ifthelowsupplyvoltagestatedoesnotexceedthisvalue,theLVRwillignorethe

lowsupplyvoltageandwillnotperformaresetfunction.TheactualVLVRvaluecanbeselected

bytheLVS7~LVS0bitsintheLVRCregister.IftheLVS7~LVS0bitsarechangedtosomecertain

valuesbytheenvironmentalnoiseorsoftwaresetting,theLVRwillresetthedeviceafteradelay

time,tSRESET.Whenthishappens,theLRFbitintheCTRLregisterwillbesethigh.Afterpoweron

theregisterwillhavethevalueof01010101B.NotethattheLVRfunctionwillbeautomatically

disabledwhenthedeviceenterstheSLEEPorIDLEmode.

LVR

Inte�nal Reset

tRSTD + tSST

Low Voltage Reset Timing Chart

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