I think I may have answered my own question -- the "SIO Tips and Tricks in PSoC® 3 / PSoC 5LP" doc says that when using a threshold other than CMOS/LVTTL that this qualifies as differential input, and not GPIO as I thought mistakenly. So - the Vih and Vil are the SIO reference +/- 0.2V.
So, I think what I actually want to do is set the threshold to 0.5*Vref (which would be 0.9V) and then Vil-Vih are 0.7-1.1V.
Can someone confirm?
You are right into the pin configuration of the SIO : you can use a threshold of Vref or 0.5*Vref (it's not the case for a basic GPIO)
The Vref could be set into your TopDesign. This value can be the output of VDAC or the internal Vref 1024V.
- Vih range : your selected threshold to VCCIO
- Vil range : 0V to your selected threshold