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Rev. 2.50 40 June 22, 2017 Rev. 2.50 41 June 22, 2017

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

A/D Flash MCU with EEPROM

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

A/D Flash MCU with EEPROM

Accumulator – ACC

TheAccumulatoriscentraltotheoperationofanymicrocontroller andiscloselyrelatedwith

operationscarriedoutbytheALU.TheAccumulatoristheplacewhereallintermediateresults

fromtheALUarestored.WithouttheAccumulatoritwouldbenecessarytowritetheresultof

eachcalculationorlogicaloperationsuchasaddition,subtraction,shift,etc.,totheDataMemory

resultinginhigherprogrammingandtimingoverheads.Datatransferoperationsusuallyinvolve

thetemporarystoragefunctionoftheAccumulator;forexample,whentransferringdatabetween

oneuserdefinedregisterandanother,itisnecessarytodothisbypassingthedatathroughthe

Accumulatorasnodirecttransferbetweentworegistersispermitted.

Program Counter Low Register – PCL

Toprovideadditionalprogramcontrolfunctions,thelowbyteoftheProgramCounterismade

accessibletoprogrammersbylocatingitwithintheSpecialPurposeareaoftheDataMemory.By

manipulatingthisregister,directjumpstootherprogramlocationsareeasilyimplemented.Loading

avaluedirectlyintothisPCLregisterwillcauseajumptothespeciedProgramMemorylocation,

however,astheregisterisonly8-bitwide,onlyjumpswithinthecurrentProgramMemorypageare

permitted.Whensuchoperationsareused,notethatadummycyclewillbeinserted.

Look-up Table Registers – TBLP, TBHP, TBLH

Thesethreespecialfunctionregistersareusedtocontroloperationofthelook-uptablewhichis

storedintheProgramMemory.TBLPandTBHParethetablepointerandindicatesthelocation

wherethetabledataislocated.Theirvaluemustbesetupbeforeanytablereadcommandsare

executed.Theirvaluecanbechanged,forexampleusingthe"INC"or"DEC"instructions,allowing

foreasytabledatapointingandreading.TBLHisthelocationwherethehighorderbyteofthetable

dataisstoredafteratablereaddatainstructionhasbeenexecuted.Notethatthelowerordertable

databyteistransferredtoauserdenedlocation.

Holtek HT66F30 User Manual

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