That shows me what I was looking for- the board is ready to accept RPM and X, Y, Z, U from the factory, but the serial is not populated. There is a header for USB, its tx traces probably go to the I/O controller, meaning it could be fed from a bluetooth module or USB, but that does no good since I can't find firmware on the Ditron site anyway. Not that there's anything wrong with mine, I just want to add features as they become available. Good to know I can tie in an RPM module if I wanted, that's something I have been wondering about. I would really like to see cutter SFM from inputted diameter along with feed speed on the display, but that's wishful thinking.