"INT 21H" in 8086 microprocessor

There are four different functions of INT 21H:

1. MOV AH, 01H

INT 21H

These two instructions together will accept one single charactor from keyboard and store it in AL register

1. MOV AH, 02H INT 21H

These two instructions will display a single charactor stored in DL register

Ex:

MOV DL41H

MOV AH, 02H

INT 21H 3. MOV AH, 09H

INT 21H

These two instructions will display an entire string stored in memory location. For this 2 conditions are must:

1. The OFFSET address of the string has to be stored in DX register 2. The string must be terminated by a $ symbol.

Ex:

LEA DX, X

MOV AH, 09H

INT 21H

Where X is a variable and string ends with the 5 sign.

4, MOV AH,4CH INT 21H

These two instructions will terminate the the program execution. But INT 3H is commonly used for this operation.