INT 10,4 - Read Light Pen Position

AH = 04

on return:

AH = 0 light pen switch not triggered

= 1 light pen triggered

BX = pixel column (0-319 or 0-639, mode dependent)

CH = raster line (0-199) (CGA and EGA modes 4, 5 and 6)

CX = raster line (EGA modes except 4, 5 and 6)

DH = row (0-24)

DL = column (0-79 or 0-79 mode dependent)

- data returned as a byte coordinate, leaving horizontal

accuracy to within 2 pixels (320) or 4 pixels (640)

- vertical accuracy within 2 lines

- PS/2's don't support the light pen interface