HT56RB688_13 datasheet(30/164 Pages) HOLTEK

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location of these registers within the Data Memory begins at the address ²00H². Any unused Data

Memory locations between these special function registers and the point where the General Purpose

Memory begins is reserved for future expansion purposes, attempting to read data from these locations

will return a unknow value.

Indirect Addressing Registers - IAR0, IAR1

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

for RAM data manipulation uses 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 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 Addressing Registers indirectly will return a result of ²00H² 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 address and track data. When any operation to the relevant

Indirect Addressing Registers 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.

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

; 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.

Bank Pointer - BP

The Data Memory is divided into a total of 32 banks. Selecting the required Data Memory area is

achieved using the Bank Pointer. If data in Bank 0 is to be accessed, then the BP register must be

loaded with the value 00H, while if data in Bank 1 is to be accessed, then the BP register must be

Rev. 1.10

April 15, 2013

HT56RB688

TinyPowerTM A/D type Smart Card OTP MCU

with LCD, DAC, ISO 7816 and USB Interfaces

HT56RB688 Datasheet(PDF) 30 Page - Holtek Semiconductor Inc

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