HT82K74EE datasheet(13/56 Pages) HOLTEK

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HT82K74E/HT82K74EE

Rev. 1.00

December 15, 2009

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 Registers

- IAR

The IAR register, located at Data Memory address

²00H², is not physically implemented. This special regis-

ter allows what is known as indirect addressing, which

permits data manipulation using a Memory Pointer in-

stead of the usual direct memory addressing method

where the actual memory address is defined. Any ac-

tions on the IAR register will result in corresponding

read/write operations to the memory location specified

by the Memory Pointer MP. Reading the IAR register in-

directly will return a result of

²00H² and writing to the

Memory Pointer

- MP

One Memory Pointer, known as MP, is physically imple-

mented in the Data Memory. The Memory Pointer can

be written to and manipulated in the same way as nor-

mal registers providing an easy way of addressing and

tracking data. When using any operation on the indirect

addressing register IAR, it is actually the address speci-

fied by the Memory Pointer that the microcontroller will

be directed to.

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 IAR

; clear the data at address defined by MP

inc mp

; 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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HT82K74EE 数据表(PDF) 13 Page - Holtek Semiconductor Inc

HT82K74EE 数据表(HTML) 13 Page - Holtek Semiconductor Inc

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