/assembly-codes

CSE 316

Primary LanguageAssembly

8086 Assembly Language

Internal Architecture of 8086 Microprocessor

General Purpose Resisters:

The 8086 microprocessor has 8 registers AH, AL, BH, BL, CH, CL, DH, DL.
Individually, these registers can store 8-bit(1 byte) data, and in pairs, they can store 16-bit(2 byte) data.
AX, BX, CX, DX

  • AX = Accumulator register (Used for I/O)
  • BX = Base register (used to store the starting base address of the memory field)
  • CX = Counter resister
  • DX = Data resister

Segment Resisters:

8086 microprocessor has 4 segment buses i.e. CS, DS, SS & ES

  • CS = Code Segment Register
  • DS = Data Segment Register
  • SS = Stack Segment Register
  • ES = Extra Segment Register

Special Purpose Resister:

  • IP = Instruction pointer

Basic Template

.MODEL SMALL
.STACK 100H

.DATA 
CR EQU 0DH
LF EQU 0AH

.CODE
MAIN PROC
    ;DATA SEGMENT INITIALIZATION, COPY DATA TO DS
    MOV AX,@DATA
    MOV DS, AX


    ;DOS EXIT
    MOV AH, 4CH
    INT 21H

MAIN ENDP
END MAIN

Exiting

keep 4CH on AH and call interupt routine 21H

;DOS EXIT
MOV AH, 4CH
INT 21H

Defining a data

  • DB stands for defined byte. (1 byte)
  • DW stands for define word. (2 byte)
  • X DB 65 sets the value of X = 'A'
  • Y DB ? sets the value of Y undefined
  • 'Hello world!!$' is a string where each letter is 1 byte/2 bytes defined by DB/DW
HW DB 'Hello world!!$'
BW DB 'Bye World!!$'
X DB 65     
Y DB ?

Printing a string

lea dx, hw
mov AH, 9 
int 21h

lea stands for load effective address.It states the start of the string to be printed.
for value 9 in AH, interupt routine 21h prints things in DX.

Printing a Character

MOV DL, CL
MOV AH, 2
INT 21H

for value 2 in AH, interupt routine 21h prints a character from DL.

Printing new line

MOV DL, CR
MOV AH, 2
INT 21H 
MOV DL, LF
INT 21H

Inputing a character

MOV AH, 1
INT 21H
MOV Y, AL

While keeping 1 at AH, Interupt routine 21H takes input from the keyboard and puts it to AL.