Assembly Programming

1. COMPUTER ORGANIZATION
& ASSEMBLY LANGUAGE
LECTURE ON 21H WEEK 13 PRACTICAL
BY MUHAMMAD JAFER
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2. INT 21H
• BIOS-ROM based
• DOS INT 21H function Calls
• Appendix D contains all of the functions
• Displaying & Inputting Function
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3. CHARACTER DISPLAY
• Option 09
• DATA1 = ‘This earth is but one country’,’$’
• AH = 09
• DX = OFFSET DATA1
• INT 21H
• Importance of $
• Option 02
• AH = 02
• DL = ‘J’
• INT 21H
• Single Character
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4. CHARACTER INPUT
• Option 01
• AH = 01
• INT 21H
• Result : AL= input Character
• Echoing
• Option 0AH
• DATA1 DUP 6,?,6 (FF)
• AH = 0AH
• DX = OFFSET DATA1
• INT 21H
• Buffer Concepts
• 1st Byte = Size of Buffer
• 2nd Byte = No of Characters
• 3rd Bytes onwards = Data
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5. CHARACTER INPUT (CONT)
• Option 07
• AH = 07
• INT 21H
• Result : AL= input Character
• No Echo
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6. LABEL DIRECTIVE
• Name LABEL Attribute
• JOE LABEL Byte
• WORD,DWORD,FWORD,QWORD,TBYTE
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7. CHAPTER REVIEW
• The x86 PC Assembly Language, Design &
Interfacing
• Chapter # 4
• BIOS INT 21H PROGRAMMING
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