DE-2 5V tolerance

[Altera_Forum]

Somebody can confirm if the DE-2 I/O expansion headers are 5V tolerant?

[Altera_Forum]

DE-2 has 47 ohm series sersistors and BAT54 schottky clamps at all GPIO pins. They basically provide a safe voltage limitation, if operating it from 5 V logic. Considering the voltage drop at the driver, the current would be limited to about 20 mA for each pin. Two problems should be considererd, however: 

 - Driving many inputs to 5V with an idle FPGA could possibly raise the 3.3V supply voltage to an dangerous level.  - With an octal driver chip, the maximum VCC current could be exceeded  A simple solution would be to use additional series resistors with slow or medium speed signals.

[Altera_Forum]

Many thanks Franck. 

 So if I understand you correctly, three or four pins should be ok, more could be risky.

[Altera_Forum]

Yes, or using additional series resistors.