HT82B42RE datasheet(44/84 Pages) HOLTEK

44 / 84 page

Rev. 1.10

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Rev. 1.10

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HT82B42R/HT82B42RE

I/O MCU with USB Interface

Oscillator

Theclocksourceforthesedevicesisprovidedbyanintegratedoscillatorrequiringnoexternal

components.Thisoscillatorhastwofixedfrequenciesofeither6MHzor12MHz,theselectionof

whichismadebytheSYSCLKbitintheSCCregister.

Watchdog Timer Oscillator

TheWDToscillatorisafullyself-containedfreerunningon-chipRCoscillatorwithatypicalperiod

of32μsat5Vrequiringnoexternalcomponents.WhenthedeviceentersthePowerDownMode,

thesystemclockwillstoprunningbuttheWDToscillatorcontinuestofree-runandtokeepthe

watchdogactive.However,topreservepowerincertainapplicationstheWDToscillatorcanbe

disabledviaaconfigurationoption.

Power Down Mode and Wake-up

Power Down Mode

AlloftheHoltekmicrocontrollershavetheabilitytoenteraPowerDownMode.Whenthedevice

entersthismode,thenormaloperatingcurrent,willbereducedtoanextremelylowstandbycurrent

level.ThisoccursbecausewhenthedeviceentersthePowerDownMode,thesystemoscillator

isstoppedwhichreducesthepowerconsumptiontoextremelylowlevels,however,asthedevice

maintainsitspresentinternalcondition,itcanbewokenupatalaterstageandcontinuerunning,

withoutrequiringafullreset.Thisfeatureisextremelyimportantinapplicationareaswherethe

microcontrollermusthaveitspowersupplyconstantlymaintainedtokeepthedeviceinaknown

conditionbutwherethepowersupplycapacityislimitedsuchasinbatteryapplications.

Entering the Power Down Mode

ThereisonlyonewayforthedevicetoenterthePowerDownModeandthatistoexecutethe

"HALT"instructionintheapplicationprogram.Whenthisinstructionisexecuted,thefollowingwill

occur:

• Thesystemoscillatorwillstoprunningandtheapplicationprogramwillstopatthe"HALT"

instruction.

• TheDataMemorycontentsandregisterswillmaintaintheirpresentcondition.

• TheWDTwillbeclearedandresumecountingiftheWDTclocksourceisselectedtocomefrom

theWDTorRTCoscillator.TheWDTwillstopifitsclocksourceoriginatesfromthesystem

clock.

• TheI/Oportswillmaintaintheirpresentcondition.

• Inthestatusregister,thePowerDownflag,PDF,willbesetandtheWatchdogtime-outflag,TO,

willbecleared.

HT82B42RE Datasheet(PDF) 44 Page - Holtek Semiconductor Inc