I'm developing a basic cable continuity tester. Essentially, the circuit drives a test vector onto the cable and reads back the output vector. The output has MOSFETs for buffers/drivers but the input is connected directly to the ICs (CPLD, in my case). My concern is ESD. Unfortunately, I have very little experience in this area and am seeking advice on how to protect my devices from ESD. One thing I saw while browsing was TVS Diodes. Reading the literature on these only confused me more. I'm not sure what the highest voltage will develop that I need protection against. I do know my CPLD will be damaged if the the IO pins see more than 4V, so that's the voltage I can tolerate. Other than that, I'm a bit confused and seeking help here. Any advice on choosing a TVS diode or, heck, another device for ESD Protection? NOTE: I am aware that a continuity tester may not be enough and I should be measuring resistances. We have a separate machine for that so we're not bothering with including that in this machine.