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HT46R92

A/D Type 8-Bit MCU with 16
16 High Current LED Driver

Holtek Semiconductor 

HT46R92

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

writeable 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 and

A/D converter operation. The location of these registers

within the Data Memory begins at the address 00H. Any

unused Data Memory locations between these special

function registers and the point where the General Pur-

pose Memory begins is reserved for future expansion

purposes, attempting to read data from these locations

will return a value of 00H.

Indirect Addressing Registers - IAR0, IAR1

The IAR0 and IAR1 registers, located at Data Memory

addresses 00H and 02H, are not physically imple-

mented. These special function registers allows what is

known as indirect addressing, which permits data ma-

nipulation using Memory Pointers instead of the usual

direct memory addressing method where the actual

memory address is defined. Any actions on the IAR0

and IAR1 registers will result in corresponding

read/write operations to the memory locations specified

by the Memory Pointers MP0 and MP1. Reading the

IAR0 and IAR1 registers indirectly will return a result of

²00H² and writing to the register indirectly will result in

no operation.

Memory Pointer - MP0, MP1

Two Memory Pointers, known as MP0 and MP1, are

physically implemented in Data Memory. The Memory

Pointer can be written to and manipulated in the same

way as normal registers providing an easy way of ad-

dressing and tracking data. When using any operation

on the indirect addressing register IAR0 or IAR1, it is ac-

tually the address specified by the Memory Pointer that

the microcontroller will be directed to.

The following example shows how to clear a section of four RAM 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

inc mp0

sdz block

jmp loop

; clear the data at address defined by MP0

; increment memory pointer

; check if last memory location has been cleared

continue:

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

Rev. 1.10

12

November 5, 2008

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