HT82B42R datasheet(13/86 Pages) HOLTEK

13 / 86 page

Rev. 1.00

October 27, 2011

Rev. 1.00

October 27, 2011

HT82B42R/HT82B42RE

I/O MCU with USB Interface

System Architecture

Akeyfactorinthehigh-performancefeaturesoftheHoltekrangeofmicrocontrollersisattributed

totheinternalsystemarchitecture.Therangeofdevicestakeadvantageoftheusualfeaturesfound

withinRISCmicrocontrollersprovidingincreasedspeedofoperationandenhancedperformance.

Thepipeliningschemeisimplementedinsuchawaythatinstructionfetchingandinstruction

executionareoverlapped,henceinstructionsareeffectivelyexecutedinonecycle,withthe

exceptionofbranchorcallinstructions.An8-bitwideALUisusedinpracticallyalloperations

oftheinstructionset.Itcarriesoutarithmeticoperations,logicoperations,rotation,increment,

decrement,branchdecisions,etc..Theinternaldatapathissimplifiedbymovingdatathroughthe

AccumulatorandtheALU.CertaininternalregistersareimplementedintheDataMemoryand

canbedirectlyorindirectlyaddressed.Thesimpleaddressingmethodsoftheseregistersalong

withadditionalarchitecturalfeaturesensurethataminimumofexternalcomponentsisrequiredto

provideafunctionalI/OandA/Dcontrolsystemwithmaximumreliabilityandflexibility.

Clocking and Pipelining

Thesystemclockisderivedfromaninternaloscillatorandissubdividedintofourinternally

generatednon-overlappingclocks,T1~T4.TheProgramCounterisincrementedatthebeginning

oftheT1clockduringwhichtimeanewinstructionisfetched.TheremainingT2~T4clockscarry

outthedecodingandexecutionfunctions.Inthisway,oneT1~T4clockcycleformsoneinstruction

cycle.Althoughthefetchingandexecutionofinstructionstakesplaceinconsecutiveinstruction

cycles,thepipeliningstructureofthemicrocontrollerensuresthatinstructionsareeffectively

executedinoneinstructioncycle.Theexceptiontothisareinstructionswherethecontentsofthe

ProgramCounterarechanged,suchassubroutinecallsorjumps,inwhichcasetheinstructionwill

takeonemoreinstructioncycletoexecute.

Forinstructionsinvolvingbranches,suchasjumporcallinstructions,twomachinecyclesare

requiredtocompleteinstructionexecution.Anextracycleisrequiredastheprogramtakesone

cycletofirstobtaintheactualjumporcalladdressandthenanothercycletoactuallyexecutethe

branch.Therequirementforthisextracycleshouldbetakenintoaccountbyprogrammersintiming

sensitiveapplications.

Program Counter

Duringprogramexecution,theProgramCounterisusedtokeeptrackoftheaddressofthenext

instructiontobeexecuted.Itisautomaticallyincrementedbyoneeachtimeaninstructionis

executedexceptforinstructions,suchas"JMP"or"CALL"thatdemandajumptoanon-consecutive

ProgramMemoryaddress.Itmustbenotedthatonlythelower8bits,knownastheProgram

CounterLowRegister,aredirectlyaddressablebyuser.

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