The switch circuit in the PBP manual shows the input pin pulled up through a 10k. That 10k then gets grounded through a switch causing a low on the input. I have noticed that the capacitance of the pin interacting with the trace inductance causes some very fast ringing. I am seeing -2Volts for about 25ns. Why is this ok? I assume it is since this is a very common method for reading switch inputs on micros and various other IC's but it violates the minimum voltage of the pin.