Are Virtex/-E I/Os 5V-tolerant? If I use a 100-ohm resistor, can a bidirectional bus interface to 5V?
When you place a 100-ohm resistor in a series with a Virtex-E pin, only the "input configured only" pin is 5V tolerant. You cannot configure the pin as an INOUT or as an OUTPUT with 5V driving that trace line. The resistor in series drops the Voh output voltage. As a result, it might not meet the input specifications of the interfacing device.
NOTES: 1. For PCI 5.0V systems, use Virtex devices or reference (Xilinx Answer 11904). 2. Never directly apply 5V to a Virtex-E pin.