Honored Contributor
Honored ContributorAltera's suggestions for your configuration are summed up in Figure 9-30 (at page 9-60 of most recent device handbook release V3.3).
There have been previous forum discussions, why the suggestions are so, and if you have to follow it strictly. Personally, I don't, but if you don't see any contradicting reasons, you simply can, because they are supposed to work. Without repeating this discussions, I want to mention two aspects: VCCA rather than VCCIO is used to set the MSEL configuration, because VCCA is monitored by the POR circuitry. The objective is to read a correct and stable configuration when POR is released. With Cyclone III, Altera is worried about the risk of damaging I/O pins by signal overshoots. This is e.g. reflected when supplying the JTAG interface by 2.5 V. There are howver alternatives like using an effective clamping circuit.
