Hi!

I was wondering what happens if you set the V9938 to screen 7 or 8 and show the various pages. Or what happens when you show pages 2 and 3 of screen mode 5... The same thing with all MSX2 modes when you have only 16kB VRAM on your V9938 like in the Yamaha CX5MII/128 and the SVI-738.... Any info on this?

If someone has such a machine, let me know, so I can ask you to do some tests on it!

Thanks in advance for the info.

That sounds really weird... IIRC the MSX-standard specifies at least 64kB VRAM for the v9938! IIRC 16kB is purely meant for MSX1!

well.. I just googled around, and some articles say the SVI-738 has a videochip with 16Kb. And the strange thing about it, it has a width80 option...

And the Msx1 vdp's doen't have that.

Only thing that bothers me though.. A screen 5 page is ~32Kb and a screen 7/8 is ~64kb... So those screens probably won't work... (but that's just a guess though)

maybe only half a screen?

Screen 6 is 32kB as well, so wolf_'s suggestion may count for that as well

In any case, screen 0 @ width 80 only takes 2kB off the 16 you have, and screen 0 @ width 40 only 1kB. So it makes sense that width 80 is possible on a SVI-738.

Oh, this was sooo long ago... :-) There was few different programs to enable width 80 and some programs to alter color pallette, but otherways I've not seen V9938 specific MSX1 software.

You can use screen 5 (page 0) in 256*128 resolution. I don't remember how it works on screen 6 / 7 (not very usefull anyway) but in screen 8 you get whole screen wide 128*128 resolution. Rest of the screen is filled with 8 pixel wide stripes. Color of the stripes is defined by first pixels on the screen. There is also something else, that I can't define, but it is scrolling down very fast. I think, that it is good idea to switch off screen when there is no data to display. You can center the "window" by using VDP reg 23. In screen 8 there is also possibility to get whole screen wide 64*212 resolution, but that is quite a useless as well...

Remember that MSX1 bios can't handle V9938 extended features, so software boot is not enough to get everything back working after messing up with registers. You have to do that on your program.

To view screen 5 pictures on 16KB VRAM, you can use this software that I made:
http://www.msx.org/modules.php?op=modload&name=Downloads&file=index&req=visit&lid=513

screen7/8 need interleaved vram. That's the whole problem.
It's currently unknown how 64K VRAM MSX2's are designed.

IMO it's the most logical they have 32K interleaved, so have 1 page of SCREEN7/8... I vaguely remember reading this a long long time ago.

Even if that would be verified and true, the question remains, what happens if you set page 2?

Afaik the manual says screen 7 and 8 are only available on VDP's with 128k of RAM. This suggests that a 64k environment does not consist out of two interleaved 32k chips but just a single 64k one. If you'd select screen 7 or 8 on a VDP like that, my guess is that you will just get a blank screen. Though of course this is all speculation .

~Grauw

I think, that with 64KB VRAM you will get two pages of screen 8 with 128*212 resolution.

The MSX2 version of Hydlide seems to support 64k vram, don't know what happens with it. Maybe a translation of the text on this flyer gives an idea what happens.

I think it says something like it switches to screen 5 (256x212x16) in case of 64k vram.

It looks like it indeed. WOW! I never knew ^_^
Would be great to see how it looks in SCREEN5

At least it's a further testament that SCREEN8 isn't usable on 64K VRAM at all.

Quote:

At least it's a further testament that SCREEN8 isn't usable on 64K VRAM at all.

If screen 8 is "usable" with 16KB VRAM (see my earlyer post), then I can't see, why it would work different with 64KB VRAM. You will just lose every other pixel... It might act differently on different computers, but at least in SVI-738 that every other pixel is a copy of pixel at left. (That is, why I say 128*212 with 2 pages is realistic.)

I meant "normally usable"...

Ok, here is the question of the day: was there any mass production MSX2 machines with 64KB VRAM? I don't think so.