I just noticed that my emulator behaves strangely with the NROM games Galaga and Dig Dug. Both of these games are vertical mirrored. Both of them put the real screen at $2000 and the rest of the nametable memory is filled with the 0 character. Galaga eventually sets the scroll to x=$F8, y=$E0. Dig Dug sets it to x=$F8, y=$08. They then set the nametable to 0 or 2 in $2000.
I thought the nametables were laid out like this:
So what ends up happening is I get 0 characters as my background instead of the correct background graphic tiles. I'm not sure why...it seems like everything is right to me. If the nametable is set to 0 or 2 and the X scroll is set to $F8 shouldn't the majority of nametable 1 or 3 be visible? Unfortunately nametable 1 and 3 are filled with zeros.
SMB and many other NROM games work flawlessly. SMB is also vertically mirrored.
Here's Dig Dug...
I thought the nametables were laid out like this:
Code:
NT0 $2000 | NT1 $2400
----------+----------
NT2 $2800 | NT3 $2C00
----------+----------
NT2 $2800 | NT3 $2C00
So what ends up happening is I get 0 characters as my background instead of the correct background graphic tiles. I'm not sure why...it seems like everything is right to me. If the nametable is set to 0 or 2 and the X scroll is set to $F8 shouldn't the majority of nametable 1 or 3 be visible? Unfortunately nametable 1 and 3 are filled with zeros.
SMB and many other NROM games work flawlessly. SMB is also vertically mirrored.
Here's Dig Dug...