HT45F2020 datasheet(20/85 Pages) HOLTEK

20 / 85 page

Rev. 1.00

April 11, 2017

Rev. 1.00

April 11, 2017

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

Special Function Register Description

MostoftheSpecialFunctionRegisterdetailswillbedescribedintherelevantfunctionalsection,

howeverseveralregistersrequireaseparatedescriptioninthissection.

Indirect Addressing Registers – IAR0, IAR1

TheIndirectAddressingRegisters,IAR0andIAR1,althoughhavingtheirlocationsinnormalRAM

registerspace,donotactuallyphysicallyexistasnormalregisters.Themethodofindirectaddressing

forRAMdatamanipulationusestheseIndirectAddressingRegistersandMemoryPointers,in

contrasttodirectmemoryaddressing,wheretheactualmemoryaddressisspecified.Actionsonthe

IAR0andIAR1registerswillresultinnoactualreadorwriteoperationtotheseregistersbutrather

tothememorylocationspecifiedbytheircorrespondingMemoryPointers,MP0orMP1.Actingasa

pair,IAR0andMP0cantogetheraccessdatafromBank0whiletheIAR1andMP1registerpaircan

accessdatafromanybank.AstheIndirectAddressingRegistersarenotphysicallyimplemented,

readingtheIndirectAddressingRegistersindirectlywillreturnaresultof“00H”andwritingtothe

registersindirectlywillresultinnooperation.

Memory Pointers – MP0, MP1

TwoMemoryPointers,knownasMP0andMP1areprovided.TheseMemoryPointersare

physicallyimplementedintheDataMemoryandcanbemanipulatedinthesamewayasnormal

registersprovidingaconvenientwaywithwhichtoaddressandtrackdata.Whenanyoperationto

therelevantIndirectAddressingRegistersiscarriedout,theactualaddressthatthemicrocontroller

isdirectedtoistheaddressspecifiedbytherelatedMemoryPointer.MP0,togetherwithIndirect

AddressingRegister,IAR0,areusedtoaccessdatafromBank0,whileMP1andIAR1areusedto

accessdatafromallbanksaccordingtoBPregister.DirectAddressingcanonlybeusedwithBank

0,allotherBanksmustbeaddressedindirectlyusingMP1andIAR1.Notethatforthedevice,bit7

oftheMemoryPointersisnotrequiredtoaddressthefullmemoryspace.Whenbit7oftheMemory

Pointersforthedeviceisread,avalueof“1”willbereturned.

ThefollowingexampleshowshowtoclearasectionoffourDataMemorylocationsalreadydefined

aslocationsadres1toadres4.

Indirect Addressing Program Example

data .section ´data´

adres1 db ?

adres2 db ?

adres3 db ?

adres4 db ?

block db ?

code .section at 0 ´code´

org 00h

start:

mov a,04h

; setup size of block

mov block,a

mova,offsetadres1 ;AccumulatorloadedwithfirstRAMaddress

movmp0,a;setupmemorypointerwithfirstRAMaddress

loop:

clrIAR0;clearthedataataddressdefinedbymp0

inc mp0

; increment memory pointer

sdz block

; check if last memory location has been cleared

jmp loop

continue:

Theimportantpointtonotehereisthatintheexampleshownabove,noreferenceismadetospecific

DataMemoryaddresses.

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