Holtek HT66F002 - Reset Functions; Power-on Reset; RES Pin Reset

Rev. 1.71 50 April 11, 2017 Rev. 1.71 51 April 11, 2017
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
Reset Functions
Thereareseveralwaysinwhichamicrocontrollerresetcanoccur,througheventsoccurringboth
internallyandexternally:
Power-on Reset
Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisrstappliedto
themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromtherst
memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown
conditions.AlltheI/Oportandportcontrolregisterswillpowerupinahighconditionensuringthat
allpinswillberstsettoinputs.


    


          

Note:t
RSTD
ispower-ondelay,typicaltime=50ms
Power-On Reset Timing Chart
RES Pin Reset
AlthoughthemicrocontrollerhasaninternalRCresetfunction,iftheV
DD
powersupplyrisetime
isnotfastenoughordoesnotstabilisequicklyatpower-on,theinternalresetfunctionmaybe
incapableofprovidingproperresetoperation.Forthisreasonitisrecommendedthatanexternal
RCnetworkisconnectedtotheRESpin,whoseadditionaltimedelaywillensurethattheRESpin
remainslowforanextendedperiodtoallowthepowersupplytostabilise.Duringthistimedelay,
normaloperationofthemicrocontrollerwillbeinhibited.AftertheRESlinereachesacertain
voltagevalue,theresetdelaytimet
RSTD
isinvokedtoprovideanextradelaytimeafterwhichthe
microcontrollerwillbeginnormaloperation.TheabbreviationSSTintheguresstandsforSystem
Start-upTimer.
FormostapplicationsaresistorconnectedbetweenV
DD
andtheRESpinandacapacitorconnected
betweenVSSandtheRESpinwillprovideasuitableexternalresetcircuit.Anywiringconnected
totheRESpinshouldbekeptasshortaspossibletominimizeanystraynoiseinterference.For
applicationsthatoperatewithinanenvironmentwheremorenoiseispresenttheEnhancedReset
Circuitshownisrecommended.
















 



Note:“*”ItisrecommendedthatthiscomponentisaddedforaddedESDprotection
“**”Itisrecommendedthatthiscomponentisaddedinenvironmentswherepowerlinenoise
issignicant
External RES Circuit