HT45F39 datasheet(15/102 Pages) HOLTEK

15 / 102 page

Rev. 1.10

July 01, 2016

Rev. 1.10

July 01, 2016

HT45F39/HT45F391

Ultrasonic Distance Measurement 8-bit Flash MCU

HT45F39/HT45F391

Ultrasonic Distance Measurement 8-bit Flash MCU

Fe tc h In st . 1E xe cu te I ns t. 1

Fe tc h In st . 2

Fl us h Pi pel in e

DE LA Y:

MO V A, [1 2H ]

CA LL D EL AY

CP L [ 12H ]

NO P

Ex ec ut e In st . 2

Fe tc h In st . 3

Fe tc h In st . 6

Ex ec ut e In s t. 6

Fe tc h In st . 7

Instruction Fetching

Program Counter

Duringprogramexecution,theProgramCounterisusedtokeeptrackoftheaddressofthe

nextinstructiontobeexecuted.Itisautomaticallyincrementedbyoneeachtimeaninstruction

isexecutedexceptforinstructions,suchas"JMP"or"CALL"thatdemandajumptoanon-

consecutiveProgramMemoryaddress.However,itmustbenotedthatonlythelower8bits,known

astheProgramCounterLowRegister,aredirectlyaddressablebyuser.

Whenexecutinginstructionsrequiringjumpstonon-consecutiveaddressessuchasajumpinstruction,

asubroutinecall,interruptorreset,etc.,themicrocontrollermanagesprogramcontrolbyloading

therequiredaddressintotheProgramCounter.Forconditionalskipinstructions,oncethecondition

hasbeenmet,thenextinstruction,whichhasalreadybeenfetchedduringthepresentinstruction

execution,isdiscardedandadummycycletakesitsplacewhilethecorrectinstructionisobtained.

Program Counter

High Byte

Low Byte (PCL Register)

PC10~PC8

PCL7~PCL0

ThelowerbyteoftheProgramCounter,knownastheProgramCounterLowregisterorPCL,is

availableforprogramcontrolandisareadableandwriteableregister.Bytransferringdatadirectly

intothisregister,ashortprogramjumpcanbeexecuteddirectly.However,asonlythislowbyteis

availableformanipulation,thejumpsarelimitedtothepresentpageofmemorythatis256locations.

Whensuchprogramjumpsareexecuted,itshouldalsobenotedthatadummycyclewillbeinserted.

ThelowerbyteoftheProgramCounterisfullyaccessibleunderprogramcontrol.Manipulatingthe

PCLmightcauseprogrambranching,soanextracycleisneededtopre-fetch.Furtherinformation

onthePCLregistercanbefoundintheSpecialFunctionRegistersection.

HT45F39 Datasheet(PDF) 15 Page - Holtek Semiconductor Inc

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