On my vg8235/00 I once had a screen 8 in 32x212 resolution. Each 8 pixels had the color of the first of 8. I will try to replicate this again.
Fascinating. Has nobody played around with this before? Almost can't be. Also very interesting to see what will happen on a 9958.
Probably it is but few people share their findings. There has also been a lot of information lost over the years.
@gdx, you are correct. In demoscene you do not really share tricks. Some info is not shared, so some info is lost.
I will check all possibilities related to M1 to M5, and unused or noted as 0 bits in the mode registers, as well as vram select.
In basic I understand when the screen goes white, the mode is invalid. In this case I do not trust Basic, will test in assembly.
Note: V9958 only, but expect V9938 behaves identical.
Get back with results, it will take some time... So don't stay up for results..
Some small update...
After analyzing the different screen modes I came to the following preliminary conclusion.
The screen modes of TMS99x8/9A and V99x8 are linked by pairs.
The ratio is always 1:4, what does this mean:
M1 & M2 (Screen 0 and Screen 3) are linked:
M1 set can can have 2 colors on X direction and Y direction (font & background). (1)
M2 has blocks of 4 x 4, 2 colors on 8 pixels, X and Y. (4)
The following modes are also linked:
M5 M4 M3
0 0 0 Screen 1 Relation not checked, TBA
0 0 1 Screen 2 Relation not checked, TBA
0 1 0 Screen 4 (2 colors in 8 pixels, 256px) (1)
0 1 1 Screen 5 (8 colors in 8 pixels, 256px) (4)
1 0 0 Screen 6 (4 colors, M5 set, M4 unset = 512) (1)
1 0 1 Screen7 (16 colors M5 set, M4 unset = 512) (4)
1 1 0 Undocumented original screen 8,
(expected 256px, 64 colors, but 256 cannot find mode to organize color bits, maybe reason to disable) (1)
1 1 1 Screen 9 (implemented as 8) 256px, 256 colors (4)
Finished routines to check possibilities I will post at: My VDP Github page
Currently only 1, to determine the amount of VRAM of the machine, MSX1+ (not V9990), can be used to determine TMS9918/28/29
Working on detecting the white screen of invalid and checking configurations of VRAM select (MSX1 and MSX2 and up), VDP R#1, R#2, R#4, R#8, R#9
Will inform updates..