When reading the NoCash NES-specs documentation I read this concerning PPU scrolling:
"after line 255 it will wrap to line 0, but without producing a carry-out to the name table address".
What does that mean, especially the last part of the sentence?
Normally: You go from scroll 239 on NT $2000 to scroll 0 on NT $2800
But if you have a scroll over 239, then you go from 255 on NT $2000 to scroll 0 on NT $2000 (not $2800, which would be logical)
Ok thanks. I was a bit confused.. Some games (Golf comes to mind) sets Y-scroll to $FF all the time. I wonder why it didn't set $00 and set the nametable it should be displaying instead, since it never scrolls anyway..(?)
Well we didn't program the game so we can't know. One reason might be so that vertical sprite offset that are rounds numbers are aligned to tiles the background. Writing $ef would be more "correct", but it will only affect the first scanline which is often considered overscan.
Slalom, TMNT, and SMB3 use negative scrolling. And probably many others.
oRBIT2002 wrote:
Some games (Golf comes to mind) sets Y-scroll to $FF all the time.
It probably pushes the background down to be aligned with the sprites, which get pushed down a line anyway.