Two types of Dreamcast RGB

[antron]

Does anyone know what the difference is between the two types of RGB signals that the DC can output?

The select pins are 6 and 7. Ground either one for two kinds of 15kHz RGB, ground both for VGA

http://www.gamesx.com/wiki/doku.php?id=av:dreamcastav

is it Jap vs EU scart pinouts?

[viletim!]

if it helps at all...

My cheapo 3rd party DC SCART lead has pin 6 connected to ground and perfectly normal RGB video comes out.

[Endymion]

I remember pestering Lawrence about this when I first saw the info here. When asked, nobody seems to know what the different modes are, or why they are even there. One mode for European RGB and another for Japanese RGB is certainly plausible, but from an engineering standpoint I do not think it is entirely necessary either as the only real difference is the pinout with gaggles of grounds on the Japanese one. It is also not very known what effect activating these different RGB modes would have on certain games, i.e. would some games work on one RGB mode and not the other. It would be interesting to know, and possibly helpful as well because there are several games I love playing that do not support RGB (or VGA) properly, but it would appear nobody has really delved into this much.

[antron]

from matt over at shmups

The mode select pins are tricky on the DC. Normally, pin 6 is grounded on DC RGB cables, and both pins 6 and 7 on VGA boxes. But, there are a few games that don't run at 15khz in this configuration (eg Skies of Arcadia) but can be tricked into working by switching off pin 7 after the game boots. They may be referring to something along these lines.

[Guest]

I not sure if I understand what you are asking, but:

The select pins are 6 and 7. Ground either one for two kinds of 15kHz RGB, ground both for VGA. Note that the Dreamcast outputs VGA, the box or cable does not �upscan�, so Dreamcast VGA boxes cannot be used for converting low-res RGB to VGA on other consoles.

15KHz = arcade type monitor
30KHz = computer type monitor.



right?

[Endymion]

That's correct Guest. The thing is, apparently the Dreamcast can have two different modes enabled for 15KHz RGB.

If what Matt says is true though, then having two 15KHz modes will still do nothing for the games that have problems with doing either 15 or 30 KHz RGB, as the cable-swap and VGA box-switching experiments have shown. Oh well.

[Darklegion]

What Matt is talking about, is tricking the dreamcast into thinking it is in VGA mode while booting but then switching it into RGB after.The VGA swap trick in reverse, basically.
I once built a cable that could switch between the 2 RGB modes, and IIRC using the second mode resulted in lower compatiblity with most games, so that seems to suggest at the least, that the modes are different.I can't seem to remember if using this second RGB mode actually fixed any of the non-RGB games though, or that it is even needed when most games can be fixed with a cable swap, or by patching the games.
I no longer have a display that supports 15KHZ rgb so I can't go and test this all again, but if any of you want to try testing this mode yourself, its an easy addition if you've already a built a cable.

[EC]

It's been a long time since I dealt with the 2 DC RGB modes but there are definitely titles which don't work in one mdoe and do work in the other and vice versa. pop'n music, Revive (IIRC) and White Illumination springs to mind as examples. Also, if you put Fighting Vipers 2 in, you'll see that the output degrades in some odd way (sorry, don't remember the details, been years!).

[Guest_SMC]

This is a little OT, but I figured it would be OK for an older thread.  I've read that not all games are VGA compatible for the Dreamcast, but I was wondering what this meant exactly.  Does it mean that some games simply don't take advantage of the higher res or does it mean that they won't run at all?

[kendrick]

For the Dreamcast to output VGA, the game has to have the software flag that allows that output type. Many of the 2D games (fighters and what not) had VGA mode disabled, and the assumption is that the developers didn't want these games displayed in a 640x480 screen since the graphics would be unnecessarily scaled up. To make matters worse, Dreamcast games that do natively support VGA mode are supposed to have that label on the back, but not all of them do. I'm sure someone out there has a definitive list of what games do and do not produce VGA, but I'm too lazy to go looking for it.

-KKC, who wasted the whole afternoon on PSU and now has to go back to work.

[blackevilweredragon]

I do a trick, that works, but is VERY hard to do..  It's a swap trick..  Start up the dreamcast with no video plug in it, wait to hear the GD-ROM beep, then plug it in...

Racketboy has a nice list..  Their site is VERY slow right now, but that's the list I go by.

http://www.racketboy.com/retro/2006/05/dre...ility-list.html

[Guest_SMC]

Thanks, both of you.  

[kendrick]

I'm closing this topic due to some spam intrusion. Please feel free to start a new one if additional discussion is desired.

-KKC