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Advanced Features of Keyboard Processing

Learn about keyboard processing, including shift status, scan codes, key types, and functions available through INT 21H and INT 16H. Understand keyboard input, buffer operations, control keys, and shift status bytes.

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Advanced Features of Keyboard Processing

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  1. Advanced Features of Keyboard Processing Suthida Chaichomchuen std@kmitnb.ac.th

  2. Introduction • Shift status byte • Scan code • Keyboard buffer area

  3. INT 21H FUNCTIONS • 01H : Keyboard input with echo • 06H : Direct console I/O • 07H : Direct keyboard input without echo • 08H : Keyboard input without echo • 0AH : Buffered keyboard input • 0BH : Check keyboard status • 0CH : Clear buffer & invoke function

  4. INT 16H FUNCTIONS • 00H : Read a character • 01H : Determine if character present • 02H : Return current shift status • 05H : Keyboard write • 10H : Read keyboard character • 11H : Determine if character present • 12H : Return current shift status

  5. Basic key types • Standard characters • A-Z, 0-9, Characters: % $ # • Extended function keys • Program function keys: <F1>, <Shift>+<F1> • Numeric keypad keys with NumLock toggled off: <Home>, <End>, <Arrows> • <Alt>+alphabetics, <Alt>+program-function keys • Control keys • <Alt>, <Ctrl>, <Shift>

  6. Keyboard shift status • Segment of data area is 40[0]H • First byte of current keyboard shift status at 40:17H • Bits set to 1 indicate following • 7 : Insert active • 6 : CapsLock state active • 5 : NumLock state active • 4 : ScrollLock state active • 3 : <Alt> pressed • 2 : <Clrt> pressed • 1 : <Left Shift> pressed • 0 : <Right Shift> pressed

  7. Keyboard shift status • Second byte for the enhanced keyboard at 40:18H • Bits set to 1 indicate following • 7 : Insert pressed • 6 : CapsLock pressed • 5 : NumLock pressed • 4 : ScrollLock pressed • 3 : Ctrl/NumLock (pause) active • 2 : SysReq pressed • 1 : Left Alt pressed • 0 : Left Ctrl pressed

  8. INT 21H Function 01H • Keyboard input with echo • Response to a <Ctrl>+<Break> request • AH = 01H • Value return • AL <> 0 : ASCII character • AL = 0 : user has pressed an extended function key • Example • MOV AH,01H • INT 21H

  9. INT 21H Function 06H • Direct console I/O • Input : load 0FFH into DL • Output : load ASCII character into DL • AH = 06H • Example • MOV AH,06H • INT 21H

  10. INT 21H Function 07H • Direct keyboard input without echo • Not response to a <Ctrl>+<Break> request • AH = 07H • Example • MOV AH,07H • INT 21H

  11. INT 21H Function 08H • Keyboard input without echo • Work like function 01H • AH = 08H • Example • MOV AH,08H • INT 21H

  12. INT 21H Function 0AH • Buffered keyboard input • Inability to accept extended function keys • AH = 0AH • Example • MOV AH,0AH • LEA DX,msg • INT 21H

  13. INT 21H Function 0BH • Check keyboard status • AH = 0BH • Return value to AL • AL = FFH : character is available • AL = 00H : no character is available • Example • MOV AH,0BH • INT 21H

  14. INT 21H Function 0CH • Clear keyboard buffer and invoke function • AH = 0CH • AL = required function • Example • MOV AH,0CH • MOV AL,function • MOV DX,kbarea • INT 21H

  15. INT 16H Function 00H • Read a character • AH = 00H • Example • MOV AH,00H • INT 16H

  16. INT 16H Function 01H • Determine whether a character is present • AH = 01H • Example • MOV AH,01H • INT 16H

  17. INT 16H Function 02H • Return the current <Shift> status • AH = 02H • AL = value return • Example • MOV AH,02H • INT 16H

  18. INT 16H Function 05H • Keyboard write • Insert characters in the keyboard buffer • AH = 05H • CH = load ASCII character • CL = load scan code • Example • MOV AH,05H • INT 16H

  19. INT 16H Function 10H • Read a keyboard character • AH = 10H • Example • MOV AH,10H • INT 16H

  20. INT 16H Function 10H • Key pressed • Regular ASCII character • AL = ASCII character • AH = scan code • Extended function key • AL = 00H • AH = scan code • Extended duplicate control key • AL = E0H • AH = scan code

  21. INT 16H Function 11H • Determine whether a character is present • Same as function 01H • accept the extended functions • AH = 11H • Example • MOV AH,11H • INT 16H

  22. INT 16H Function 12H • Return the current keyboard shift status • Similar to function 02H • AH = 12H • Example • MOV AH,12H • INT 16H

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