On Cyclone II FPGAs can I apply voltage directly on input pins, maybe taking it from a Vcc pin? Or should I use a resistor? The Altera DE2 board's schematics below looks like some input switches don't use resistors.
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In general, all modern devices have high-impedance inputs so they will draw very little current from the source. Therefore, a series resistor is unneeded if the pin is always an input. The danger is if you might accidentally program the pin as an output, set low. In this case, with no resistor, the result is high current flow through the pin and potential damage to the device.
Placing a series resistor protects the device in case of mis-programming.
I should also note that on many FPGAs, an I/O bank may have a different voltage than Vcc, so you would connect to the appropriate Vio instead of Vcc.
