2013
PPU scrolling - Nesdev wiki
by sylvainulgGames scroll to show an area much larger than the 256x240 pixel screen [...] Write the starting page (high order bit of X and Y) to bits 0 and 1 of PPUCTRL ($2000) [...] you write that to VRAM before you set the scroll, as seen in the animation below.
2008
1
(2 marks)