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Rev. 2.50 38 June 22, 2017 Rev. 2.50 39 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

Special Function Register Description

MostoftheSpecialFunctionRegisterdetailswillbedescribedintherelevantfunctionalsection,

howeverseveralregistersrequireaseparatedescriptioninthissection.

Indirect Addressing Registers – IAR0, IAR1

TheIndirectAddressingRegisters,IAR0andIAR1,althoughhavingtheirlocationsinnormalRAM

forRAMdatamanipulationusestheseIndirectAddressingRegistersandMemoryPointers,in

contrasttodirectmemoryaddressing,wheretheactualmemoryaddressisspecied.Actionsonthe

IAR0andIAR1registerswillresultinnoactualreadorwriteoperationtotheseregistersbutrather

tothememorylocationspeciedbytheircorrespondingMemoryPointers,MP0orMP1.Actingasa

pair,IAR0andMP0cantogetheraccessdatafromBank0whiletheIAR1andMP1registerpaircan

accessdatafromanybank.AstheIndirectAddressingRegistersarenotphysicallyimplemented,

readingtheIndirectAddressingRegistersindirectlywillreturnaresultof"00H"andwritingtothe

registersindirectlywillresultinnooperation.

Memory Pointers – MP0, MP1

TwoMemoryPointers,knownasMP0andMP1areprovided.TheseMemoryPointersare

physicallyimplementedintheDataMemoryandcanbemanipulatedinthesamewayasnormal

registersprovidingaconvenientwaywithwhichtoaddressandtrackdata.Whenanyoperationto

therelevantIndirectAddressingRegistersiscarriedout,theactualaddressthatthemicrocontroller

isdirectedto,istheaddressspeciedbytherelatedMemoryPointer.MP0,togetherwithIndirect

AddressingRegister,IAR0,areusedtoaccessdatafromBank0,whileMP1andIAR1areusedto

accessdatafromallbanksaccordingtoBPregister.DirectAddressingcanonlybeusedwithBank0,

allotherBanksmustbeaddressedindirectlyusingMP1andIAR1.NotethatfortheHT66F20and

HT66F30devices,bit7oftheMemoryPointersisnotrequiredtoaddressthefullmemoryspace.

Whenbit7oftheMemoryPointersforHT66F20andHT66F30devicesisread,avalueof"1"will

bereturned.

ThefollowingexampleshowshowtoclearasectionoffourDataMemorylocationsalreadydened

aslocationsadres1toadres4.

Holtek HT66F30 User Manual

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