Sega Mega Drive/Scrolling

The Sega Mega Drive is able to scroll the background and foreground (planes B & A) independently, both horizontally and vertically.

Horizontal scrolling

Horizontal scrolling is controlled by a table located in VRAM. The address for the table is set by VDP register $0D, while the format is set by register $0B. There are three possible settings for this register:

Type	Space in VRAM	Format	Code
Whole screen	4 bytes	FFFF BBBB 1st word controls foreground 2nd word controls background	move.w #$8B00,($c00004).l
8 pixel strips	112 ($70) bytes (NTSC) 120 ($78) bytes (PAL)	FFFF BBBB FFFF BBBB FFFF BBBB... Alternating words control foreground and background strips	move.w #$8B02,($c00004).l
Per scanline	896 ($380) bytes (NTSC) 960 ($3C0) bytes (PAL)	FFFF BBBB FFFF BBBB FFFF BBBB... Alternating words control foreground and background scanlines	move.w #$8B03,($c00004).l