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  Interrupt:   16h     Functions:  02h and 12h
 
  Title:       Get Keyboard Flags
 
  See also:    Keyboard Data Memory
 
  Description:                                          [PC] [AT] [PS/2]
 
     Returns flag data that describes the state of the various keyboard
     toggles and shift keys. Use Function 02h if the code must work
     with any keyboard. Use Function 12h if the code must handle the
     additional keys of the enhanced keyboard (such as right CTRL and
     ALT). You can use the keyboard data byte at 0000:0496h to determine
     if the extended keyboard is available.
 
     The low byte returned by 02h and 12h is the same as the keyboard
     flags byte stored at 0000:0417h. The high byte returned by
     Function 12h is similar to (but not exactly the same as) the byte
     stored at 0000:0418h.
 
     Input                       Output
 
     AH = 02h for shift flags    AL = Flags (both 02h and 12h)
        = 12h for extended
          shift flags             7 6 5 4 3 2 1 0
                                 ┌─┬─┬─┬─┬─┬─┬─┬─┐
                                 │ │ │ │ │ │ │ │ │
                                 └─┴─┴─┴─┴─┴─┴─┴─┘
                                  │ │ │ │ │ │ │ │
                                  │ │ │ │ │ │ │ └─ Right SHIFT key is down
                                  │ │ │ │ │ │ └─── Left SHIFT key is down
                                  │ │ │ │ │ └───── CTRL key is down
                                  │ │ │ │ └─────── ALT key is down
                                  │ │ │ └───────── SCROLL LOCK on
                                  │ │ └─────────── NUM LOCK on
                                  │ └───────────── CAPS LOCK on
                                  └─────────────── INS on
 
                                 AH = Extended flags (12h only)
 
                                  7 6 5 4 3 2 1 0
                                 ┌─┬─┬─┬─┬─┬─┬─┬─┐
                                 │ │ │ │ │ │ │ │ │
                                 └─┴─┴─┴─┴─┴─┴─┴─┘
                                  │ │ │ │ │ │ │ │
                                  │ │ │ │ │ │ │ └─ Left CTRL key is down
                                  │ │ │ │ │ │ └─── Left ALT key is down
                                  │ │ │ │ │ └───── Right CTRL key is down
                                  │ │ │ │ └─────── Right ALT key is down
                                  │ │ │ └───────── Scroll key is down
                                  │ │ └─────────── NUM LOCK key is down
                                  │ └───────────── CAPS LOCK key is down
                                  └─────────────── SYSREQ key is down
                                    -♦-