Question
I plan to power port 1 at 3.3V. But I need to interface to a Xilinx Virtex-6
FPGA. I wonder if setting a 2.5V voltage for the SCL, SDA signals in port 1
would work or if it would produce overcurrents somewhere.
Answer
This configuration will not damage any parts on the bus. As long as the VIL is
compatible with your output, you can do it. The pull-ups would simply be
referenced to the 2.5V supply.