HT45F56 datasheet(41/90 Pages) HOLTEK

41 / 90 page

Rev. 1.11

April 11, 2017

Rev. 1.11

April 11, 2017

HT45F56

Shock Detector Flash MCU

HT45F56

Shock Detector Flash MCU

Power-on Reset

Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedto

themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirst

memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown

conditions.AlltheI/Oportandportcontrolregisterswillpowerupinahighconditionensuring

thatallpinswillbefirstsettoinputs.

VDD

Power-on Reset

SST Time-out

tRSTD

Note:tRSTDispower-ondelaywithtypicaltime=50ms

Power-On Reset Timing Chart

RES Pin Reset

AlthoughthemicrocontrollerhasaninternalRCresetfunction,iftheVDDpowersupplyrisetimeis

notfastenoughordoesnotstabilisequicklyatpower-on,theinternalresetfunctionmaybeincapable

ofprovidingproperresetoperation.ForthisreasonitisrecommendedthatanexternalRCnetwork

isconnectedtotheRESpin,whoseadditionaltimedelaywillensurethattheRESpinremainslowfor

anextendedperiodtoallowthepowersupplytostabilise.Duringthistimedelay,normaloperation

ofthemicrocontrollerwillbeinhibited.AftertheRESlinereachesacertainvoltagevalue,thereset

delaytimetRSTDisinvokedtoprovideanextradelaytimeafterwhichthemicrocontrollerwillbegin

normaloperation.TheabbreviationSSTinthefiguresstandsforSystemStart-upTimer.

FormostapplicationsaresistorconnectedbetweenVDDandtheRESpinandacapacitorconnected

betweenVSSandtheRESpinwillprovideasuitableexternalresetcircuit.Anywiringconnected

totheRESpinshouldbekeptasshortaspossibletominimizeanystraynoiseinterference.For

applicationsthatoperatewithinanenvironmentwheremorenoiseispresenttheEnhancedReset

Circuitshownisrecommended.

MoreinformationregardingexternalresetcircuitsislocatedinApplicationNoteHA0075Eonthe

Holtekwebsite.

VDD

RES

10kO~

100kO

0.01µF**

1N4148*

VSS

0.1µF~1µF

300O*

Note:“*”ItisrecommendedthatthiscomponentisaddedforaddedESDprotection.

“**”Itisrecommendedthatthiscomponentisaddedinenvironmentswherepowerlinenoise

issignificant.

External RES Circuit

HT45F56 Datasheet(PDF) 41 Page - Holtek Semiconductor Inc

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