Connecting system bit by bit, I have just connected parallel cable and USB lead to breakout board, I have a "?" in Mach3 in Device manager also on breakout board the long terminal block has 5v going to TB6600 stepper drivers but cant find any reference to the connection next to this 5v the "GND" going anywhere, have you any idea if this should connect to the general 0volt of the power supplies or is it a PC only ground, and is opto coupled on the breakout board.
Regards John