HT68F03 datasheet(20/139 Pages) HOLTEK

20 / 139 page

HT66F03/HT66F04/HT68F03/HT68F04

Rev. 1.00

April 16, 2010

Special Function Register Description

Most of the Special Function Register details will be de-

scribed in the relevant functional section, however sev-

eral registers require a separate description in this

section.

Indirect Addressing Registers

- 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 Pointers, MP0 or MP1. Acting as a

pair, IAR0 and MP0 can together access data from Bank

0 while the IAR1 and MP1 register pair can access data

from any bank. 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 Pointers

- MP0, MP1

Two Memory Pointers, known as MP0 and MP1 are pro-

vided. 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. MP0, together with Indirect

Addressing Register, IAR0, are used to access data

from Bank 0, while MP1 and IAR1 are used to access

data from all banks according to BP register. Direct Ad-

dressing can only be used with Bank 0, all other Banks

must be addressed indirectly using MP1 and IAR1. Note

that for this series of devices, the Memory Pointers,

MP0 and MP1, are both 8-bit registers and used to ac-

cess the Data Memory together with their corresponding

indirect addressing registers IAR0 and IAR1.

The following example shows how to clear a section of

four Data Memory locations already defined as loca-

tions adres1 to adres4.

· 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:

The important point to note here is that in the example shown above, no reference is made to specific RAM addresses.

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