My XEM3005 is producing a square wave at around 2 Mhz on one of the GP IO pins (JP4-63). The XEM is plugged into the BRK3005 breakout board. My oscilloscope is registering a lot of ringing on the rising and falling edges with overshoot up to ± 2 V. Is there some immediate way to suppress this?
FPGAs produce very fast edges. There are several documents available from Xilinx that discuss signal integrity issues and I would refer you to them for details.
You also adjust the ourput slew rate (SLOW will help) and drive current (choose a lower drive current). Then try terminating the end of the line with a reasonable resistance to dampen overshoot.