Spartan3 I/O question

There are diodes on each I/O that will prevent that I/O from going above VCCO or below GND by more than a "diode drop".

If the resistor is large enough you won't do any damage, but you won't get the high level voltage you're expecting.

Bob

Hi,

I was thiking that I use these outputs as static signals but even with a week pullup (100KOhm), it seem that the high voltage will still not reach to 3.3V unless, I use external voltage translator from 1.8 to

Thanks.

CP

The output may not need to reach 3.3V depending on the load. 3.3V logic often has a Vih (min) of 2.0V like TTL. The additional diode drop on top of 1.8V can get you to about 2.3V, but you'll need a smaller pullup than 100K to get there.

on the other hand, a single-gate logic device in SOT23 or similar package can do the job nicely without the stress on the protection diodes. Your choice (obviously).

regards, Gabor