Assembly Language Help (alang.hlp) (Table of Contents; Topic list)
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Int 10h Function 04h
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  Interrupt:   10h     Function:   04h
 
  Title:       Get Light Pen Position
 
  Description:                                        [CGA] [PCjr] [EGA]
 
     Obtains the current status and position of the light pen.
 
     Input        Output
 
     AH = 04h     AH = 00h (if light pen not down/not triggered)
                     = 01h (if light pen down/triggered)
                  BX = Pixel column (graphics x coordinate)
                  CH = Pixel row
                       (graphics y coordinate, modes 04h-06h)
                  CX = Pixel row
                       (graphics y coordinate, modes 0Dh-10h)
                  DH = Character row (text y coordinate)
                  DL = Character column (text x coordinate)
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