HT45F39 datasheet(29/102 Pages) HOLTEK

29 / 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

Special Function Register Description

MostoftheSpecialFunctionRegisterdetailswillbedescribedintherelevantfunctionalsection,

howeverseveralregistersrequireaseparatedescriptioninthissection.

Indirect Addressing Registers – IAR0, IAR1

TheIndirectAddressingRegisters,IAR0andIAR1,althoughhavingtheirlocationsinnormalRAM

registerspace,donotactuallyphysicallyexistasnormalregisters.Themethodofindirectaddressing

forRAMdatamanipulationusestheseIndirectAddressingRegistersandMemoryPointers,in

contrasttodirectmemoryaddressing,wheretheactualmemoryaddressisspecified.Actionsonthe

IAR0andIAR1registerswillresultinnoactualreadorwriteoperationtotheseregistersbutrather

tothememorylocationspecifiedbytheircorrespondingMemoryPointer,MP0orMP1.Actingas

apair,IAR0withMP0andIAR1withMP1,cantogetheraccessdatafromtheDataMemory.As

theIndirectAddressingRegistersarenotphysicallyimplemented,readingtheIndirectAddressing

Registersindirectlywillreturnaresultof"00H"andwritingtotheregistersindirectlywillresultin

nooperation.

Memory Pointers – MP0, MP1

TwoMemoryPointers,knownasMP0andMP1areprovided.TheseMemoryPointersare

physicallyimplementedintheDataMemoryandcanbemanipulatedinthesamewayasnormal

registersprovidingaconvenientwaywithwhichtoaddressandtrackdata.Whenanyoperationto

therelevantIndirectAddressingRegistersiscarriedout,theactualaddressthatthemicrocontroller

isdirectedto,istheaddressspecifiedbytherelatedMemoryPointer.MP0,MP1togetherwith

IndirectAddressingRegister,IAR0,IRA1areusedtoaccessdata.Notethatbit7oftheMemory

Pointersisnotrequiredtoaddressthefullmemoryspace.Whenbit7oftheMemoryPointersfor

thesedevicesisread,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

mov

a, offset adres1 ; Accumulator loaded with first RAM address

mov

mp0, a

; setup memory pointer with first RAM address

loop:

clr

IAR0

; clear the data at address defined by MP0

inc

mp0

; increment memory pointer

sdz

block

; check if last memory location has been cleared

jmp

loop

continue:

Theimportantpointtonotehereisthatintheexampleshownabove,noreferenceismadetospecific

DataMemoryaddresses.

HT45F39 Datasheet(PDF) 29 Page - Holtek Semiconductor Inc

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