HT82A620R datasheet(13/72 Pages) HOLTEK

13 / 72 page

HT82A520R/HT82A620R

Rev.1.00

October 23, 2009

Special Purpose Data Memory

This area of Data Memory is where registers, necessary

for the correct operation of the microcontroller, are

stored. Most of the registers are both readable and

writable but some are protected and are readable only,

the details of which are located under the relevant Spe-

cial Function Register section. Note that for locations

that are unused, any read instruction to these addresses

will return the value

²00H².

Special Function Registers

To ensure successful operation of the microcontroller,

certain internal registers are implemented in the Data

Memory area. These registers ensure correct operation

of internal functions such as timers, interrupts, etc., as

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

location of these registers within the Data Memory be-

gins at the address 00H. 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 00H.

Indirect Addressing Register

- IAR0, IAR1

The IAR0 and IAR1 register, although having their loca-

tions in normal RAM register space, do not actually

physically exist as normal registers. The method of indi-

rect addressing for RAM data manipulation uses these

Indirect Addressing Registers and Memory Pointers, in

contrast to direct memory addressing, where the actual

memory address is specified. Actions on the IAR0 and

IAR1 registers will result in no actual read or write opera-

tion to these registers but rather to the memory location

specified by their corresponding Memory Pointer, MP0

or MP1. Acting as a pair, IAR0 and MP0 can together

only access data from Bank 0, while the IAR1 and MP1

Bank 1. As the Indirect Addressing Registers are not

physically implemented, reading the Indirect Ad-

dressing Registers indirectly will return a result of

²00H²

and writing to the registers indirectly will result in no op-

eration.

Memory Pointer

- MP0, MP1

For all devices, 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 pro-

viding a convenient way with which to address and track

data. When any operation to the relevant Indirect Ad-

dressing Registers is carried out, the actual address that

the microcontroller is directed to, is the address speci-

fied by the related Memory Pointer.

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 ad-

dresses.

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