I've worked out the rest of the X positioning code, but I'll post and comment on it later.Y position is a little trickier. First, there are two partial zones at the top and the bottom of the screen. Second, the partial zones will affect the effective Y position of the other sprites.Last night I rediscovered how to do vertical motion on the 7800 again (0,0 is the top left corner) and realized I had to add any Y adjustments to the sprite in order to make the DL index calculation work. This means the Y adjustment is the height of the last zone and an increasing Y adjustment appear to move towards the bottom of the background. (So, again 0,0 is the top left corner of the background.)I have a nasty feeling that the partial zones are going to make wrap around mucho difficult, but that's a task for another day.I'm also cross-posting much of this to http://www.livejournal.com/users/spacewar_a78, although I'll leave out the in-depth code discussions over there.