HT82M75R_1011 Datasheet, PDF (14/66 Pages) Holtek Semiconductor Inc – I/O Type 8-Bit OTP MCU

HT82M75R/HT82M75RE
HT82K75R/HT82K75RE
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 Register - 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 Pointer, MP0 or MP1. Acting as a
pair, IAR0 and MP0 can together only access data from
Bank 0, while the IAR1 and MP1 register pair can ac-
cess data from all of the data banks if the Data Memory
is divided into 2 or more banks. As the Indirect Ad-
dressing Registers are not physically implemented,
reading the Indirect Addressing Registers indirectly will
return a result of ²00H² and writing to the registers indi-
rectly will result in no operation.
Memory Pointer - MP0, MP1
For all devices, 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 pro-
viding a convenient way with which to address and track
data. When any operation to the relevant Indirect Ad-
dressing Registers is carried out, the actual address that
the microcontroller is directed to, is the address speci-
fied by the related Memory Pointer. MP0 can only ac-
cess data in Bank 0 while MP1 can access all data
banks if the Data Memory is divided into 2 or more
banks.
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 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 Data Memory ad-
dresses.
Rev. 1.30
14
November 24, 2010