When the keyboard forces a hardware interrupt, it passes a Scan Code to
the INT 09H interrupt handler.  The handler converts this to an ASCII or
Extended ASCII value.  For compatibility across the various keyboards, it
is wise to avoid using scan codes and stick to the BIOS translation of a
keystroke.

  Original PC/XT Keyboard  
When a key is released, the keyboard sends the same value, ORed with 80H
(e.g., [Ctrl] sends 1dH when pressed and 9dH when released).

                                                                            
Hex Dec Key  Hex Dec Key   Hex Dec Key     Hex Dec Key     Hex Dec Key
                                                                            
01   1  Esc  12  18  E     23  35  H       34  52  . >     45  69  NumLock
02   2  1 !  13  19  R     24  36  J       35  53  / ?     46  70  ScrollLck
03   3  2 @  14  20  T     25  37  K       36  54  Shft(R) 47  71  Home [7]
04   4  3 #  15  21  Y     26  38  L       37  55  * PrtSc 48  72       [8]
05   5  4 $  16  22  U     27  39  ; :     38  56  Alt     49  73  PgUp [9]
06   6  5 %  17  23  I     28  40  " '     39  57  space   4a  74  K -
07   7  6 ^  18  24  O     29  41  ` ~     3a  58  CapsLck 4b  75       [4]
08   8  7 &  19  25  P     2a  42  Shft(L) 3b  59  F1      4c  76       [5]
09   9  8 *  1a  26  [ {   2b  43  \ |     3c  60  F2      4d  77       [6]
0a  10  9 (  1b  27  ] }   2c  44  Z       3d  61  F3      4e  78  K +
0b  11  0 )  1c  28  Enter 2d  45  X       3e  62  F4      4f  79  End  [1]
0c  12  - _  1d  29  Ctrl  2e  46  C       3f  63  F5      50  80       [2]
0d  13  + =  1e  30  A     2f  47  V       40  64  F6      51  81  PgDn [3]
0e  14  bksp 1f  31  S     30  48  B       41  65  F7      52  82  Ins  [0]
0f  15  Tab  20  32  D     31  49  N       42  66  F8      53  83  Del  [.]
10  16  Q    21  33  F     32  50  M       43  67  F9      
11  17  W    22  34  G     33  51  , <     44  68  F10     
                                                                            
K indicates a key on the numeric keypad  (when not in NumLock mode)

  84-key AT Keyboard  
The 84-key keyboard sends the same scan codes as the 83-key (original PC)
keyboard with the addition that

[SysReq] sends scan code 54H (84 decimal).

However, the BIOS never lets an application program see this scan code.
Instead, it invokes INT 15H 85H on make or break of the SysReq key.

The 'break' (release of a key) is handled differently.  Upon a break, the
keyboard sends a two-byte sequence:  0f0H, followed by the 'make' scan
code.  See AT Keyboard Functions for information on programming this
keyboard.

  101-key Keyboard  
This keyboard has three separate mappings of the scan codes, selected by
communication through port 64H.  The keyboard comes to life with scan code
set 2 (which is wildly different from the 84-key mapping.  However, the
scan codes are translated by the hardware keyboard interface before they
are made available to programs that read the keyboard.

The result is that all of the scan codes identified in the above table are
valid when the 101-key 'board comes up naturally.  The following table
lists the additional scan-codes that are sent by the 101-key 'board.  Note
that all keys mentioned here refer to the keys that are unique to this
keyboard; e.g., [Insert] is the dedicated insert key (not KeyPad Ins).

                                                                        
Key                       Hex Sequence        Key           Hex Sequence
                                                                        
F11 ..................... 57                  Home ........ e0 47
F12 ..................... 58                  Shft-Home ... e0 aa e0 47
Right-Alt ............... e0 38               End ......... e0 4f
Right-Ctrl .............. e0 1d               Shft-End .... e0 aa e0 4f
PrintScreen ............. e0 2a e0 37           ........... e0 48
Shft-PrintScreen (SysReq) e0 37               Shft-  ...... e0 aa e0 48
Ctrl-PrintScreen (SysReq) e0 37                 ........... e0 50
Alt-PrintScreen ......... 54                  Shft-  ...... e0 aa e0 50
Pause ................... e1 1d 45 e1 9d c5   PageUp ...... e0 49
Ctrl-Pause (Break) ...... e0 46 e0 c6         Shft-PageUp . e0 aa e0 49
Insert .................. e0 52               PageDown .... e0 51
Shft-Insert ............. e0 aa e0 52         Shft-PageDown e0 aa e0 51
Delete .................. e0 53                 ........... e0 4d
Shft-Delete ............. e0 aa e0 53         Shft-  ...... e0 aa e0 4d
  ....................... e0 4b               K Enter ..... e0 1c
Shft-  .................. e0 aa e0 4b         K / ......... e0 35
  Shft-K / .... e0 aa e0 35
                                                                        
K indicates a key on the numeric keypad 

Note that in cases where a key is similar to another (pre-101) key, the
second scan code byte is the same as the original key.  Thus, some
programs that work at the scan-code level can get away with simply
ignoring the e0H prefix.

See Also: INT 09H
- -

Keyboard Scan Codes