HT82K75R datasheet(14/66 Pages) HOLTEK

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HT82M75R/HT82M75RE

HT82K75R/HT82K75RE

Rev. 1.10

June 11, 2010

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 Indirect Addressing Registers, IAR0 and IAR1, al-

though having their locations in normal RAM register

space, do not actually physically exist as normal regis-

ters. The method of indirect addressing for RAM data

manipulation uses these Indirect Addressing Registers

and Memory Pointers, in contrast to direct memory ad-

dressing, where the actual memory address is speci-

fied. 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 specified by their corre-

sponding 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 register pair can ac-

cess data from all of the data banks if the Data Memory

is divided into 2 or more banks. As the Indirect Ad-

dressing Registers are not physically implemented,

reading the Indirect Addressing Registers indirectly will

return a result of

²00H² and writing to the registers indi-

rectly will result in no operation.

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. MP0 can only ac-

cess data in Bank 0 while MP1 can access all data

banks if the Data Memory is divided into 2 or more

banks.

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 mp,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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