Sorry for double posting but I didn't understand something.
Lets say I set a map plane A location, how big will it be? Does it end where the next one (ie map window) starts? Or maybe it depends on how much data I put there?
This register you should be concerned with...
Register 10 (90) - "Map Plane Size":
W and X bits are used together respectively, and so are Y and Z bits.
Now the way to understand this is by seeing a graphical example:
The red and green squares represent the Map Planes, while the blue rectangle represents the screen, here's the rule, the screen can move anywhere within the plane area (The red square), if the screen crosses any of the red lines, the other side of the plane will present, basically looping/wrapping itself.
If the screen goes out one side, it'll enter the other side is the simplest way to put it.
This register controls how big the plane size is.
If WX is 00, then the vertical plane size is 32 cells/tiles big (32 x 8 pixels).
If WX is 01, then the vertical plane size is 64 cells/tiles big (64 x 8 pixels).
If WX is 11, then the vertical plane size is 128 cells/tiles big (128 x 8 pixels).
10 is prohibited for WX.
If YZ is 00, then the horizontal plane size is 32 cells/tiles big (32 x 8 pixels).
If YZ is 01, then the horizontal plane size is 64 cells/tiles big (64 x 8 pixels).
If YZ is 11, then the horizontal plane size is 128 cells/tiles big (128 x 8 pixels).
10 is prohibited for YZ too.
No matter what size you have the planes, they will always wrap in a loop should the screen advance out of the boundary area.
if for example WX is 00 and YZ is 01 then the map plane size is "Vertical x Horizontal" 32 x 64 tiles large (20 x 40 in hex), each tile's map is worth two bytes, so the simple math here is: "Vertical x Horizontal = S x 2 = A" (20 x 40 = 800 x 2 = 1000
1000 bytes would be the size, so if you have the plane A location set to C000, the map area would be between C000 and CFFF.
Also what kind of data is in there (I assume enigma mappings)?
No, Enigma is the name given to a decompression algorithm used frequently by SEGA, it is used to reduce the size of data in the MC68 rom, this map data is decompressed from Enigma into a ram space somewhere and then sent to V-Ram as uncompressed, the VDP in the megadrive is not able to decompress Enigma's algorithm.
And, are the registers all you had to explain for vdp and that's it, from here on its just questions we ask?
It wouldn't be called "The VDP Questions Topic" otherwise =P