This thread is an offshoot from a thread on Photonlexicon where we'd been discussing the forthcoming FB4 and the protocol over cat5. Bill responded with the following to one of my questions: Ultimately, I want to know if there is a spare pair in the FB4 implementation to carry my estop signal. I currently run my estop over pins 4/17 of the ILDA cable, and each projector has relays connected to the safety board and also onto the pass through connector, so I can have a single estop work effectively on a chain of projectors. I have 7 projectors with this configuration and I'm not looking to change it. If I can run my estop over spare pair on the cat5 I can break it out at the stage and build an ILDA breakout box for each DAC output, which has a separate relay on each output, controlled by the single input from the cat5. As I stated in the thread on PL, I'm only really interested in FB4 for cat5 at all if I can utilize the cat5 for estop. I don't really want to swap multiple ILDa runs for multiple cat5 runs. I've looked at the Startech USB extenders but I believe they use their own proprietary protocol which leaves no pair spare.