COE205

1

• COE-205
• Computer Organization Assembly Language
• Section 56
• Experiment3

2
Outline

• Review
• Basic Input/Output

3
Assembly Language Syntax(Directives)
4
Review
TITLE prog.asm .MODEL SMALL .STACK
200 .Data NUM1 DB 2 NUM2 DB 4 .CODE MOV
AX,_at_DATA MOV DS,AX MOV AL,NUM1 MOV
BL,NUM2 MOV AX,4C00H INT 21H END

0B01
STACK
0A3C
DATA
MOV AX,_at_DATA MOV DS,AX MOV AL,NUM1 MOV
BL,NUM2 MOV AX,4C00H INT 21H
0A3B
OCDE
5
Review

STACK
0A3C
DATA
MOV AX,_at_DATA MOV DS,AX MOV AL,NUM1 MOV
BL,NUM2 MOV AX,4C00H INT 21H
0A3C
OCDE
6
ASCII Table
7
How is doing it?

• Do you think that the program does I/O itself?

Program
OS
BIOS, Drivers
HW
8
INT 21H

• Do you remember ?
• MOV AH,4CH
• INT 21H
• That was one function(4CH) of INT 21H, to exit
  the program.

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Other INT 21H Functions
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Function 01H

• MOV AH,01H
• INT 21H
• Now, AL contains the ASCII code of the read
  character

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Function 08H

• MOV AH,08H
• INT 21H
• Now, AL contains the ASCII code of the read
  character, but no echo on the screen

12
Function 02H/06H

• MOV DL,A or MOV DL,41H or MOV DL,010000001B
• MOV AH,02H
• INT 21H
• Now, the character is now on the screen

13
Function 09H

• .DATA
• MSG DB Hello,0DH,0AH,
• .CODE
• LEA DX,MSG or MOV DX,OFFSET MSG
• MOV AH,09H
• INT 21H
• Now, the String is on the screen

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Function 0AH

• Before you read a String you must prepare the
  buffer for it.
• Buffer size the max string to be read1
• Actual size the actual of char read.

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Function 0AH (Read Student ID)

• .DATA
• Id DB 7,8 DUP(?)
• .CODE
• LEA DX, Id or MOV DX,OFFSET Id
• MOV AH,0AH
• INT 21H
• Now, the String is in memory pointed by Std_ID

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Function 0AH (Read Student ID)

• .If the use input 201456