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As I mentioned earlier I'll need to use a voltage translator in order to work with 3.3V logic (correct me if I'm wrong).
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You need to review the Cyclone V data sheet for the electrical characteristics of the I/Os.
http://www.altera.com/literature/hb/cyclone-v/cv_51002.pdf Look at p11, "Table 14. Single-Ended I/O Standards for Cyclone V Devices", note that a 2.5V I/O bank has a VIL(max) = 1.7V and VIH(max) = 3.6V.
Look at p3, "Table 2. Maximum Allowed Overshoot During Transitions for Cyclone V Devices", the 100% duty cycle limit is 3.7V.
According to these parameters, you can drive the 2.5V logic inputs with 3.3V. So long as your inputs are "well-behaved" (no overshoot or ringing that violates Table 2), then you do not need buffers.
That being said, it is sometimes "better to be safe than sorry", so its your call.
Cheers,
Dave
Honored Contributor
