Honored Contributor
Honored ContributorPX devices are said to support 50 MHz down to 2.3 V, but they are not fully compatible to EPCS respectively M25Pnn devices, e.g. missing the electronic signature expected by the Quartus programmer. There may be ways to use it as AS configuaration memory though. I have no urgent need for 2.5V AS devices now, however. I simply stay with 3.3V operation for part of the IO banks.
P.S.: As Altera is permanently emphasizing the problems of 3.3V VCCIO with 65 nm devices, they should be more motivated to find a suitable solution for 2.5V AS configuration, I think.
