INT 0x10 - 0x04 - Read Light Pen Position

Not available on VGA

Request/Call:

reg	value	descr
AH	0x04

reg	descr
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)
on a CGA, returned column numbers are always multiples of 2 (320-column modes) or 4 (640-column modes)
vertical accuracy within 2 lines
PS/2's don't support the light pen interface