I want to set up bg 2 in mode 1 to create a scrollable background. The bg is
made from a complete image so there
is no tile repetion and it is divided it in tiles only to be usable it in
this mode. The bg is also horizontally wrappale.
The background image is 256x120 so with 256 unique tiles I can only cover an
area of 256x64 pixels, 32x8tiles.

But I've found a rom that use 2 different char base blocks (block 2 and 3)
on the same bg (well int the bg register
only block 3 is addressed... but the final result requires the tile data
from both) and I've no idea how to setup a
thing like that (and from the documentation I've read a thing like that is
not possible).

I've dumped the the screen base block used by bg 2 (7). The first part look
like that

0x6003800: 00 01 02 ........................ 0F
0x6003810: 10 11 12 ........................ 1F
and so on..
0x60038F0: F0 F1 F2 ........................ FF

and that's clear beacuse it's addressing every tile in a linear way.
The second part is equal to the first but reach only the line in D0 D1 ...
then turn to FF FF FF.. till address 0x6003c00

What's strange is that the first part address tiles in char block 2 and the
second in char block 3!

Please, help!!