HT45FM2C datasheet(18/171 Pages) HOLTEK

18 / 171 page

Rev. 1.10

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Rev. 1.10

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HT45FM2C

Brushless DC Motor Flash Type 8-Bit MCU

HT45FM2C

Brushless DC Motor Flash Type 8-Bit MCU

Preliminar�

System Architecture

Akeyfactorinthehigh-performancefeaturesoftheHoltekrangeofmicrocontrollersisattributed

totheirinternalsystemarchitecture.Therangeofdevicestakeadvantageoftheusualfeaturesfound

withinRISCmicrocontrollersprovidingincreasedspeedofoperationandenhancedperformance.

Thepipeliningschemeisimplementedinsuchawaythatinstructionfetchingandinstruction

executionareoverlapped,henceinstructionsareeffectivelyexecutedinonecycle,withthe

exceptionofbranchorcallinstructions.An8-bitwideALUisusedinpracticallyallinstructionset

operations,whichcarriesoutarithmeticoperations,logicoperations,rotation,increment,decrement,

branchdecisions,etc.TheinternaldatapathissimplifiedbymovingdatathroughtheAccumulator

andtheALU.CertaininternalregistersareimplementedintheDataMemoryandcanbedirectly

orindirectlyaddressed.Thesimpleaddressingmethodsoftheseregistersalongwithadditional

architecturalfeaturesensurethataminimumofexternalcomponentsisrequiredtoprovidea

functionalI/OandA/Dcontrolsystemwithmaximumreliabilityandflexibility.Thismakesthis

devicesuitableforlow-cost,high-volumeproductionforcontrollerapplications.

Clocking and Pipelining

Themainsystemclock,derivedfromeitheraHIRCorLIRCoscillatorissubdividedintofour

internallygeneratednon-overlappingclocks,T1~T4.TheProgramCounterisincrementedatthe

beginningoftheT1clockduringwhichtimeanewinstructionisfetched.TheremainingT2~T4

clockscarryoutthedecodingandexecutionfunctions.Inthisway,oneT1~T4clockcycleforms

oneinstructioncycle.Althoughthefetchingandexecutionofinstructionstakesplaceinconsecutive

instructioncycles,thepipeliningstructureofthemicrocontrollerensuresthatinstructionsare

effectivelyexecutedinoneinstructioncycle.Theexceptiontothisareinstructionswherethe

contentsoftheProgramCounterarechanged,suchassubroutinecallsorjumps,inwhichcasethe

instructionwilltakeonemoreinstructioncycletoexecute.

Forinstructionsinvolvingbranches,suchasjumporcallinstructions,twomachinecyclesare

requiredtocompleteinstructionexecution.Anextracycleisrequiredastheprogramtakesone

cycletofirstobtaintheactualjumporcalladdressandthenanothercycletoactuallyexecutethe

branch.Therequirementforthisextracycleshouldbetakenintoaccountbyprogrammersintiming

sensitiveapplications.

Fe tc h In st . ( PC )

Ex ec ut e In st . (P C- 1)

Fe tc h In st . (P C+ 1)

Ex ec ut e In st . (P C)

Fe tc h In st . (P C+ 2)

Ex ec ut e In st . (P C+ 1)

PC +1

PC +2

f SY S

(S yst em C lo ck)

P has e Cl o ck T1

Pr ogr am C oun te r

P has e Cl o ck T2

P has e Cl o ck T3

P has e Cl o ck T4

Pi pe lin in g

System Clocking and Pipelining

HT45FM2C Datasheet(PDF) 18 Page - Holtek Semiconductor Inc

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