Activating Clamping Diodes

[Altera_Forum]

Hi you all, 

Does anybody know how to activate the clamping diodes in quartus II? I am trying to configurate a Cyclone EP1C6 and I need to turn on that option since I want to interface my FPGA with a 5V device.  I also would like to know if the clamping diodes are available for all I/O pins, or if it is only available for those I/O Banks that allow the PCI I/O standard.  Thanks diriver63

[Altera_Forum]

Hello, 

 to my knowledge, PCI clamp diode is available for all Cyclone pins, the same with Cyclone II: It can be enabled in Assignment Editor or Pin Planner (after activating the PCI-IO column). But I never used it, mainly for the following restriction, that makes the option effectively useless in interfacing 5V signals to my opinion:    --- Quote Start ---  Because 5.0-V tolerance in Cyclone devices require the use of the PCI clamping diode, and the clamping diode is only available after configuration has finished, be careful not to connect 5.0-V signals to the device. (From Cyclone devive handbook)  --- Quote End ---    I suggest to use resistive dividers or 74LVC buffers instead.  Regards, Frank