Connection between Cyclone III with ATXmega or HC series logic device

First - thank you for your reply.

At this moment this is just prototype of student project. I am afraid, that i set pins of both devices (Xmega and Cyclone) as outputs with different logic states. Data bus is bidirectional. I wonder if 120 Ohm resistors (just like on development boards) are enough. With 3V difference it can deliver 40mA into FPGA on single pin, and data bus contains 16 pins. Maybe i should use buffer (like 74hc245)?

This 40mA current is the reason, why i didn't use 0,063W resistor ladder while connecting buttons into fpga.