Here is my parallax scrolling engine that i've implemented, into my Mega Man II port on the Super Nintendo.
For vertical scroll, I simply have bg1 $210E sent to bg2 $2110 so they match. Right now bg2 is simply a manual paste of tiles into the SNES vram, tilemap is 64x32.
Just imagine what this will look like with updated gfx and cgram down the road.
Enjoy my playthrough. 🙂