How To Print Text In 8086 Assembly : Code Explained

This program prints simple text on screen in 8086 assembly language. Click to download the code

Printing a text in assembly language is very easy.

In assembly language we need to build a logic and then write a program. In this program we only need to print a simple message for which we have written this code.

1. First we write the title of program so that we can understand the purpose of program

TITLE TEXT_MESSAGE

2. Then we define the model, model is the part of program which tells assembler which model we need to use for our program. In this program we are using SMALL, but there are many like TINY, SMALL and LARGE

.MODEL SMALL

3. Then we define the stack of program. STACK usually tells assembler that how much bytes we need to use for our DATA SEGMENT (explained later). In this program we have used 100 bytes in hexadecimal

.STACK 100H

4. Now comes the DATA SEGMENT, which, we define as .DATA. in DATA SEGMENT we store our variables and temporary data. For example our temporary bytes. In this program we have stored an array of characters containing our message.

That’s how you define a array of characters (string) in assembly.

NAME	TYPE	“MESSAGES$”
MSG	DB	0AH, 0DH, "TEXT MESSAGE$"

MSG is the name of message you can have any name, DB is DEFINE BYTE (will be explained further in variables section) and then our text message. You notice 0AH and 0DH these bytes are for carriage return and line feed, now the message which is in quotes, be careful for dollar sign ($), which is string terminator, do not forget to add it after every message.

5. After setting up DATA SEGMENT, CODE SEGMENT starts, which tells assembler that our program has been started. We define CODE SEGMENT same as we defined DATA SEGMENT.

.CODE

In the code segment first we define a label from which our program starts, in this program we have defined MAIN: with colon. Then we move starting address of DATA SEGMENT by using AX register in to DS register (will be explained later programs). First move address to AX register then mov it back to DS register.

MOV AX, @DATA

MOV DS, AX

6. To print the message we need to move its address to DX register there are two way to do it but we will use OFFSET command to do it. After moving address to DX register we store 09H byte in AH register to tell assembler that we want to print a string. Now we invoke interrupt service routine by using INT 21H

MOV DX, OFFSET MSG

MOV AH, 09H

INT 21H

7. Now that we have completed the task of string printing we need to tell assembler that where to end the program for this we simply define another label name EXIT: with colon and move 4CH byte in AH register and invoke INT 21H after this we use END MAIN (without colon)

EXIT:

MOV AH, 04CH

INT 21H

END MAIN

Here is the complete program.

TITLE TEXT_MESSAGE 
.MODEL SMALL 
.STACK 100H 
.DATA 
    MSG DB 0AH, 0DH, "TEXT
MESSAGE$"
.CODE 
    MAIN: 
        MOV AX, @DATA 
        MOV DS, AX
         
        MOV DX, OFFSET MSG 
        MOV AH, 09H 
        INT 21H        
         
  ;     LEA DX, MSG 
  ;     MOV AH, 09H 
  ;     INT 21H 
         
             
         
    EXIT:     
        MOV AH, 04CH 
        INT 21H 
    END MAIN