Undocumented Mode 1 + 2 : Poll/Discussion

Enlighted (6935)

26-02-2007, 18:48

Let's poll.

Who thinks this mode should be freely used for developing MSX games ?

For those who do not know what I am asking about:
http://bifi.msxnet.org/msxnet/tech/tms9918a.txt
:P

I remember someone collected some data about how many msx users
cannot see this mode on ther HW.
What was the conclusion?

By SLotman

Paragon (1242)

26-02-2007, 19:28

There are already lot's of games that use it. Mostly adventure games, that use text on bottom of the screen, and graphics on middle-top... I dont see why not used it.

If some computers cant show it, too bad

By jltursan

Prophet (2619)

26-02-2007, 23:25

This mode is very much like Mode 1; the difference is that there can be three
different pattern tables, and control register #4 has a different meaning.

The pattern table now has 3 x 256 patterns; the screen is divided in three
parts (the top 8 character rows, the middle 8, the bottom 8). Each part can
use a different part of the pattern generator table (the first 256, the second
256, the last 256). The top part always uses the first 256 patterns in the PG.

Control register #4:
bit 7 - 3 : ignored
bit 2 : PG13; if set, PG = 2000h otherwise 0
bit 1 : if set, the last 8 rows use the 3rd pattern table otherwise 1st.
bit 0 : if set, the middle 8 rows use the 2nd pattern table otherwise 1st.

This undocumented mode is not available in the V9938 as far as I know.

Funny; but in fact it works flawlessly!

I've just re-tested some games that I believe they use the in-famous mix mode (only one set of patterns) and they work as expected on a NMS8245. The games are "Picture Puzzle" and "Stratos".

AFAIK the MSX2/2+ VDP processor are free of the common quirks of the MSX1 VDPs.

Since now, the only "fake" VDP I've found is the Toshiba T6950

Look at this [url=http://www.msxgamesbox.com/karoshi/index.php?topic=566.0]thread[/thread]

There are already lot's of games that use it. Mostly adventure games, that use text on bottom of the screen, and graphics on middle-top...

Comercial ones?, do you remember the titles?

By dvik

Prophet (2200)

26-02-2007, 23:38

First of all, I wouldn't call this a hybrid screen mode if you're only playing with R3 and R4 (as I think this topic is talking about). The screen mode bits are the three M bits in R0 and R1. The R3 and R4 bits controls addressing and this so called hybrid mode is just plain screen 2 with mirroring (not a hybrid). You can check out this topic to see real hybride screen modes.

I'm using R4 mirroring it in the GnG port :)

By dvik

Prophet (2200)

26-02-2007, 23:50

The real hybrid modes are MSX1 only. The V9938 does not support these screen modes. My guess is that on a TMS9918, each of the M1-M3 bits controls a specific feature, like if its 1 or three parts on the screen or whether to use 40/32 chars per scanline. On V9938 I think the M bits are used more like a table lookup so the undocumented combinations are not supported at all.

By ARTRAG

Enlighted (6935)

26-02-2007, 23:57

Ok we can agree that the s.c. mode 1+2 isn't actually a new mode, but rather a way to force
mode 2 to address 3 times the same bank of tiles.
This name comes from the document from Sean Young, who was one of the first that documented it.
But now, the question stay the same how many users cannot see it ?

It seems that all the msx2 and upper support it, and, AFAIK, the large majority of msx1 models.
Is only the T6950 that misses this "mode"?
How many users have this chip in their msx, nowaday (when all of us use emulators ;-)

By dvik

Prophet (2200)

27-02-2007, 00:20

I heard that almost all MSX1 models has a VDP that supports this mirroring. The concern I have is that I would like to use both R3 and R4 mirroring but that seems to screw up the sprites somehow. I didn't really understand how the mirroring of the sprites work.

I don't think its any problem at all assuming that all MSXes support R4 mirroring (just ignore the rare machine(s) where its not working).

Someone said that there are some problems with R3 mirroring and I would love to hear more about that (can't remember who said it, I think someone at the karoshi forum but I can't find it).

By jltursan

Prophet (2619)

27-02-2007, 01:28

Maybe here? (url screwed up in my last post :P)

By PlainSpooky

Resident (53)

27-02-2007, 02:16

I've been using this trick since 1992 on TMS99x8, v9938 and V9958 and I didn't have any problems. On early MSX emulators, it didn't work properlly, but now their bug has been solved.

Here's a sample, at MSXRio's website: http://msxrio.cipsga.org.br/files/ffym2_dsk.lha (brazilian portuguese only)

By ARTRAG

Enlighted (6935)

27-02-2007, 09:32

Hi PlainSpooky, which program in your DSK uses the trick?

By cax

Prophet (3740)

27-02-2007, 09:57

I have somewhere font generation tool that saves a MSX-BASIC program with the colorful font you've created and sets the "1+2" mode. Basic thinks it's in SCREEN1, so you can even continue editing your program while being in this mode.
A lot of games and educational programs were written in USSR using this mode and the mentioned tool. Having such a symbols as building blocks you can make very compact graphical screens, and manipulating them is easy even in Basic.