Input logic level on Spartan 3?

I?m wondering if its possible to directly input a 0 ? 5 volt logic level signal to a input pin on a Spartan 3?

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Yes you can even input 1000MegaVolts to problem (o;

No seriously..the Spartan 3 chips only allow 3.3V IO voltage max. Have you read any datasheets yet?


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logic level

There have been other threads on this. The short answer is no - at least not directly. Xilinx says you can use a series resistor and let the Vcco clamp diode limit the input voltage. Other approaches include using a MOSFET buffer ("Quickswitch") or a resistor divider.

Also when you say 0 - 5 volt, remember that the output of 5 volt logic doesn't usually drive to the Vcc rail. CMOS devices like FCTxxxT indicate "TTL compatible" meaning both input threshold and output drive. You may be able to get away without a resistor on these since they can be very wimpy above 3.5 volts, but it's much safer to put in the resistor in case you get the chip with a slightly higher Voh or have power-on sequencing issues (5V coming up first).

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