Hi you all!
> Oberleithner Wolfgang <[EMAIL PROTECTED]> wrote:
>
> Does anybody know how the Video-Ram-contents is changed
> depending on the settings of the moderegisters?
>
> mode registers:
> M5/1 - Screen select
> 00000 Screen 1
> 00001 Screen 0 (WIDTH 40)
> 00010 Screen 3
> 00100 Screen 2
> 01000 Screen 4
> 01001 Screen 0 (WIDTH 80)
> 01100 Screen 5
> 10000 Screen 6
> 10100 Screen 7
> 11100 Screen 8
>
As far as I know, there is NO DIRECT influence from these VDP mode
registers on the VRAM, they only control how the VDP handles it
(display, command execution). So changing these does not do anything
with the VRAM, set these bits back, and the VRAM is still the same.
2 remarks here:
-Ofcourse it might have an influence on an already running
VDP-command. Sounds a like a good way to screw up VRAM contents:
start some VDP block command, and then toggle some of those mode
bits, while it's running. Might be a nice way to produce all kinds of
beautifull screen patterns....
-For most screens, there is a relationship between the exact VRAM
address, and the VRAM page/pixel-coordinates that is about what you
would expect. In some screen modes (I think Graphic 5 & 6 modes, that
is, SCREEN 6 & 7), this relationship is different, so the contents of
for instance 2 SCREEN 5-pages is not visible in one SCREEN 7-page,
but 're-arranged' somehow (does anyone know how exactly?). In SCREEN
8, this is 'back to normal'.
>
> Is there any relation between the _SINGLE_ bits and the vdp-behaviour?
>
> f.e. bit 1 set: maximum 256 colors (unset: 16 colors)
> bit 2 set: display 128 bytes per line (unset: 256 bytes)
> ...
Hey, I guess there must be, because it's all implemented in hardware
somehow...
V9938 databook doesn't tell, so this is 'undefined'. Only way to find
out is to investigate a real V9938, and no guarantees it will work
the same in for instance a V9958 (or other compatible?)
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx
http://www.twente.nl/~cce
****
MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put
in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the
quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
****
