Step and enable outputs (not the direction outputs) are via fast (<1μs) opto-isolators, and all finally emerge finally via cmos buffers powered from the cnc domain 5V, which is directly linked to the ...

The limit switch pairs go in the square loops in the diagram (one shown open circuit = triggered) D1, 2 and 3 are the internal opto-isolator leds, and the opto-isolator output transistors (not shown) ...