HT66F25D datasheet(53/177 Pages) HOLTEK

53 / 177 page

A/D Flash Type 8-bit MCU with EEPROM

HT66F24D/HT66F25D

Rev. 1.00

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Rev. 1.00

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Reset Functions

Therearefivewaysinwhichamicrocontrollerresetcanoccur,througheventsoccurringboth

internallyandexternally:

Power-on Reset

Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedto

themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirst

memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown

conditions.AlltheI/Oportandportcontrolregisterswillpowerupinahighconditionensuringthat

allpinswillbefirstsettoinputs.

RE S

VD D

In te r nal R es et

0. 9 V DD

t RS TD + t SST

Power-On Reset Timing Chart

Note:tRSTDispower-ondelay,typicaltime=50ms

Low Voltage Reset – LVR

Themicrocontrollercontainsalowvoltageresetcircuitinordertomonitorthesupplyvoltageofthe

device.TheLVRfunctionisalwaysenabledwithaspecificLVRvoltageVLVR.Ifthesupplyvoltage

ofthedevicedropstowithinarangeof0.9V~VLVRsuchasmightoccurwhenchangingthebattery,

theLVRwillautomaticallyresetthedeviceinternallyandtheLVRFbitintheCTRLregisterwill

alsobesetto1.ForavalidLVRsignal,alowsupplyvoltage,i.e.,avoltageintherangebetween

0.9V~VLVRmustexistforatimegreaterthanthatspecifiedbytLVRintheA.C.characteristics.Ifthe

lowsupplyvoltagestatedoesnotexceedthisvalue,theLVRwillignorethelowsupplyvoltageand

willnotperformaresetfunction.TheactualVLVRvaluecanbeselectedbytheLVSbitsintheLVRC

LVRwillresetthedeviceafter2~3LIRCclockcycles.Whenthishappens,theLRFbitintheCTRL

registerwillbesetto1.Afterpowerontheregisterwillhavethevalueof01010101B.Notethatthe

LVRfunctionwillbeautomaticallydisabledwhenthedeviceentersthepowerdownmode.

LV R

In te r nal R es et

t RS TD + t SST

Low Voltage Reset Timing Chart

Note:tRSTDispower-ondelay,typicaltime=100ms

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