ACEX 1K family device 5V compatible input

Hi All,

I am having problem with a ACEX 1K device (EP1K50) for a legacy design. In the ACEX 1K family datasheet. It specified that PCI clamping diode must be DISABLED on an input which is driven with a voltage higher than VCCIO...In my case, the input has a pull-up to 5V and the VCCIO is 3.3V..So to my understanding that I need to DISABLE the PCI clamping diodes. Recently we have several boards all failed on this IO (shorted to GND) and I couldn't find any more detailed information regarding to how the clamping diode works inside the ACEX 1K family. However, on Altera FPGA devices (for example Cyclone II), a similar diode exists, but here in Cyclone II handbook, it suggested that for such inputs, the diode should be ENABLED with a series resistor to limit the current flow through the diode.

Am I getting conflict information here or I am comparing apple with orange? Also, since the original design was done by someone else, how can I check (in Quartus II), if these clamping diodes are indeed enabled or disabled?

Thanks

E