huge image display problem

[RockinB]

I want to display a 704x448 pixel image using double interlace and high resolution.

It works fine using a bitmap scroll of size 1024x512 with 8bpp color palette. Unfortunately this consumes the whole VDP2 VRAM (well, almost: lines 448-511 unused -> 64kByte free). Storing the image consecutively using linescroll and vertical cell scroll feature does not work, since vertical cell scroll can't be used in hires mode.

Okay, so I'm using the tile method. But it seems that the number of cells (88x56 + 1) is too much, as the image is not displayed correctly.

So I increased the pattern name data size from 1 word to 2 words resulting in more of the image diplayed correctly. Then I switched character size from 1x1 to 2x2 and now about 65 percent of the image (top half) shows correct. Removing duplicate characters improves it, too.

Obviously there must be a cell address overflow, but I don't understand how the address is computed by the VDP2.

Is there any solution to display a scroll with (up to) 4928 different cells?

Possibly I could use 2 scrolls, but I don't want to.

BTW: the MapEditor does by far not allow to use this much characters, but BGCON can create it

 

[RockinB]

Could it be a problem if character pattern data fills not only bank A completely, but bank B partially, too?

 

[RockinB]

Okay, it works now. I could determine that only VRAM bank A0 content was displayed and so I supplied some hand-made VRAM cycle patterns and now it looks fine .