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Advanced Features of Keyboard Processing

Advanced Features of Keyboard Processing. Suthida Chaichomchuen std@kmitnb.ac.th. Introduction. Shift status byte Scan code Keyboard buffer area. INT 21H FUNCTIONS. 01H : Keyboard input with echo 06H : Direct console I/O 07H : Direct keyboard input without echo

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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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