2.5VCCIO and 1.8V logic

[Altera_Forum]

Hi, 

  I am designing a board using the EP3C40F324C6N device. The A/D converter that I am using has an LVDS data bus and 1.8V control logic. If I have VCCIO connected to 2.5V (which is required for LVDS), can the same IO bank accept 1.8V logic? The app notes that I have found all deal with the incoming logic voltage being higher than VCCIO not lower than VCCIO.   Thanks   Bob

[Altera_Forum]

Look at page 1-11 of volume 2 chapter 1 of the CyIII device handbook (http://www.altera.com/literature/hb/cyc3/cyc3_ciii52001.pdf) It looks like the 2.5 I/O bank will work of with 1.8V inputs. However, be aware that this I/O bank will output 2.5V, which may or may not play well with the external device (A/D?).

[Altera_Forum]

--- Quote Start ---   If I have VCCIO connected to 2.5V (which is required for LVDS), can the same IO bank accept 1.8V logic?   --- Quote End ---    It could work but you have to keep a few things in mind: - Like Ironmoose wrote: be aware that the output will be 2.5V - The minimum Vih of a 2.5V bank is 1.7V - The Voh of your external device will be close to 1.8V in practice, but your datasheet will probably specify 0.7*Vcc or so. So not enough - A pull-up resistor to 2.5V on the input signals could give these a last step. - The noise margin (difference between Voh and Vih) will be very small - The use of a schmitt trigger input will improve the noise insensitivity  Good luck, Ton  PS Maybe the bus hold functionality could be use, but I don't have any experience with it

[Altera_Forum]

Thanks for the advice!