HT83F02 datasheet(16/64 Pages) HOLTEK

16 / 64 page

HT83F02

Rev. 1.20

November 19, 2010

well as external functions such as I/O data control. The

location of these registers within the Data Memory be-

gins at the address

²00H². Any unused Data Memory lo-

cations between these special function registers and the

point where the General Purpose Memory begins is re-

served and attempting to read data from these locations

will return a value of

²00H².

Indirect Addressing Register

- IAR0

The Indirect Addressing Registers, IAR0, although hav-

ing their locations in normal RAM register space, do not

actually physically exist as normal registers. The

method of indirect addressing for RAM data manipula-

tion uses these Indirect Addressing Registers and Mem-

ory Pointers, in contrast to direct memory addressing,

where the actual memory address is specified. Actions

on the IAR0 registers will result in no actual read or write

operation to these registers but rather to the memory lo-

cation specified by their corresponding Memory Pointer,

MP0. As the Indirect Addressing Registers are not phys-

ically implemented, reading the Indirect Addressing

Registers indirectly will return a result of

²00H² and writ-

ing to the registers indirectly will result in no operation.

Memory Pointer

- MP0

For all devices, two Memory Pointers, known as MP0 is

provided. These Memory Pointers are physically imple-

mented in the Data Memory and can be manipulated in

the same way as normal registers providing a conve-

nient way with which to address and track data. When

any operation to the relevant Indirect Addressing Regis-

ters is carried out, the actual address that the

microcontroller is directed to, is the address specified by

the related Memory Pointer.

The following example shows how to clear a section of four Data Memory locations already defined as locations adres1

to adres4.

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:

The important point to note here is that in the example shown above, no reference is made to specific Data Memory

addresses.

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