HT82B42RE datasheet(39/84 Pages) HOLTEK

39 / 84 page

Rev. 1.10

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Rev. 1.10

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HT82B42R/HT82B42RE

I/O MCU with USB Interface

USB Interrupt

TheUSBinterruptsaretriggeredbythefollowingUSBeventscausingtherelatedinterruptrequest

flag,USBF,tobeset.

• AccessofthecorrespondingUSBFIFOfromPC

• AUSBsuspendsignalfromthePC

• AUSBresumesignalfromthePC

• AUSBResetsignal

Whentheinterruptisenabled,thestackisnotfullandtheUSBinterruptisactive,asubroutine

calltolocation04Hwilloccur.Theinterruptrequestflag,USBF,andtheEMIbitwillbeclearedto

disableotherinterrupts.

WhenthePCHostaccessestheFIFOofthedevice,thecorrespondingrequestbit,USR,isset,and

aUSBinterruptistriggered.SotheusercaneasydeterminewhichFIFOhasbeenaccessed.When

theinterrupthasbeenserved,thecorrespondingbitshouldbeclearedbyfirmware.Whenthedevice

receiveaUSBSuspendsignalfromHostPC,thesuspendline(bit0ofUSC)issetandaUSB

interruptisalsotriggered.

AlsowhendevicereceiveaResumesignalfromHostPC,theresumeline(bit3ofUSC)issetanda

USBinterruptistriggered.

Serial Interface Interrupt

TheSerialInterfaceInterrupt,alsoknownastheSPIinterrupt.ASPIInterruptrequestwilltakeplace

whentheSPIInterruptrequestflag,SIF,isset,whichoccurswhenabyteofdatahasbeenreceived

ortransmittedbytheSPIinterface.Toallowtheprogramtobranchtoitsrespectiveinterruptvector

address,theglobalinterruptenablebit,EMI,andtheSerialInterfaceInterruptenablebit,ESII,must

firstbeset.Whentheinterruptisenabled,thestackisnotfullandabyteofdatahasbeentransmitted

orreceivedbytheSPIinterface,asubroutinecalltotherespectiveInterruptvector,willtakeplace.

WhentheSerialInterfaceInterruptisserviced,theEMIbitwillbeautomaticallyclearedtodisable

otherinterrupts,andtheinterruptrequestflag,SIF,willbealsoautomaticallycleared.

Reset and Initialisation

Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicecanbeset

tosomepredeterminedconditionirrespectiveofoutsideparameters.Themostimportantreset

conditionisafterpowerisfirstappliedtothemicrocontroller.Inthiscase,internalcircuitrywill

ensurethatthemicrocontroller,afterashortdelay,willbeinawelldefinedstateandreadyto

executethefirstprograminstruction.Afterthispower-onreset,certainimportantinternalregisters

willbesettodefinedstatesbeforetheprogramcommences.OneoftheseregistersistheProgram

Counter,whichwillberesettozeroforcingthemicrocontrollertobeginprogramexecutionfromthe

lowestProgramMemoryaddress.

Inadditiontothepower-onreset,situationsmayarisewhereitisnecessarytoforcefullyapply

aresetconditionwhenthemicrocontrollerisrunning.Oneexampleofthisiswhereafterpower

hasbeenappliedandthemicrocontrollerisalreadyrunning,theRESlineisforcefullypulledlow.

Insuchacase,knownasanormaloperationreset,someofthemicrocontrollerregistersremain

unchangedallowingthemicrocontrollertoproceedwithnormaloperationaftertheresetlineis

allowedtoreturnhigh.AnothertypeofresetiswhentheWatchdogTimeroverflowsandresetsthe

microcontroller.Alltypesofresetoperationsresultindifferentregisterconditionsbeingsetup.

AnotherresetexistsintheformofaLowVoltageReset,LVR,whereafullreset,similartotheRES

resetisimplementedinsituationswherethepowersupplyvoltagefallsbelowacertainthreshold.

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