AH = 03h
        AL = 0: reset typematic (PCjr)
        AL = 1: increase initial delay (PCjr)
        AL = 2: increase continuing delay (PCjr)
        AL = 3: increase both delays (PCjr)
        AL = 4: turn off typematic (PCjr)
        AL = 5: Set typematic rate (AT or PS/2)
          BH = 00 - 03 for delays of 250ms, 500ms, 750ms, or 1s
          BL = 00 - 1F for typematic rates of 30cps down to 2cps
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