EMC - minimill IO - Spindle forward IO mapping

To which pin on the parallel port is spindle forward mapped (default) with
minimill IO? I only have 1 parallel port and currently only use 4 outputs
for 2 stepper motors (x and y). I am building a plasma table and want to use
the spindle forward to turn the torch on.

What exactly does this entry in the .ini file do?

SPINDLE_FORWARD_INDEX = 1


Thanks,
Terry