HT46R0664 datasheet(21/92 Pages) HOLTEK

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HT46R0664

Enhanced A/D+LCD 8-Bit OTP MCU

Special Function Register

Most of the Special Function Register details will be described in the relevant functional section.

However several registers require a separate description in this section.

Indirect Addressing Registers – IAR0, IAR1

The Indirect Addressing Registers, IAR0 and IAR1, although having their locations in normal RAM

for RAM data manipulation is using 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 operation to these registers but rather

to the memory location specified by their corresponding Memory Pointers, MP0 or MP1. Acting as a

pair, IAR0 and MP0 can together access data from Bank0 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 Addressing Registers indirectly will return a result of “00H” and writing to the

registers indirectly will result in no operation.

Memory Pointers – MP0, MP1

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 providing a convenient way with which to indirectly address and track data. MP0 can

only be used to indirectly address data in Bank 0 while MP1 can be used to address data in Bank 0,

Bank 1 and Bank 2. When any operation to the relevant Indirect Addressing Registers is carried out,

the actual address that the microcontroller is directed to, it is the address specified by the related

Memory Pointer.

Indirect Addressing Program Example

data . section ‘data’

adres1

adres2

adres3

adres4

block

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 addresses.

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