Holtek HT66F30 - Page 41

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.