I was able to chase down a PDF on mine (older model) you should be able to do the same.
Look at your "ports and pins" in Mach3. It will be obvious if you have any inputs spare. There are only five available. 10 - 13 and 15
Usually just looking at the BoB will give a good indication. Look for white printing on the board.
Just as an example here is a pic of the older model taken from the PDF. Note the white printing.
Greg |