Int 10 Fn 04  - Video - Read Light Pen Position (except VGA)               [V]

   AH = 04h

Return: AH = light pen trigger flag
       00h not down/triggered
       01h down/triggered
       DH,DL = row,column of character light pen is on
       CH = pixel row (graphics modes 04h-06h)
       CX = pixel row (graphics modes with >200 rows)
       BX = pixel column
Desc:  determine the current position and status of the light pen (if
     present)

Notes: on a CGA, returned column numbers are always multiples of 2 (320-
     column modes) or 4 (640-column modes)
   returned row numbers are only accurate to two lines