A Question about Dreamcast 15KHz via VGA

dmauro · Post by **dmauro** » Mon Aug 18, 2008 5:51 pm

I know I can't get Bangai-o running at 31KHz VGA, but is there a way I can force the system into 15KHz without modifying the VGA box to play Bangai-o on a tri-sync monitor?

iatneH · Post by **iatneH** » Mon Aug 18, 2008 7:49 pm

The Dreamcast A/V port has a RGB enable line, and a VGA enable line. Most VGA boxes tie the two lines together, so you cannot toggle them independently without replacing the switch.

I am guessing a SCART cable has the RGB line pulled low and VGA select disconnected, so you could use a SCART cable with a custom cable end for whatever monitor you use.

dmauro · Post by **dmauro** » Mon Aug 18, 2008 8:00 pm

So what you're saying is I could use a SCART cable that terminates in a VGA connector? Would this still be capable of 31KHz? The goal is a VGA connector that can do 15 or 31KHz depending on what the game wants to run at.

edit: I suppose I could also mod the vga box with a manual 15/31KHz switch right?

iatneH · Post by **iatneH** » Mon Aug 18, 2008 9:08 pm

dmauro wrote:So what you're saying is I could use a SCART cable that terminates in a VGA connector? Would this still be capable of 31KHz? The goal is a VGA connector that can do 15 or 31KHz depending on what the game wants to run at.

edit: I suppose I could also mod the vga box with a manual 15/31KHz switch right?

A simple SCART cable ending in a VGA connector should work, but I am not exactly sure which of the original Hsync and Vsync pins should be connected to Csync. It would also no longer be capable of 31 KHz.

If your VGA box has a slide switch of some sort, chances are it is a DPST. Replacing the single DPST with two SPST switches will allow you to toggle RGB select and VGA select independently. However, there is still the issue of where to send Csync in RGB mode. I don't know if the Dreamcast automatically re-routes it, so the mod could be a bit more involved.

Keep in mind I am in Canada and have never owned a RGB monitor, as such I have never done any 15 KHz RGB stuff so I am just guessing here...

dmauro · Post by **dmauro** » Mon Aug 18, 2008 10:14 pm

Yes, it has a switch to go from the VGA out to the composite out. Does anyone know how to do this mod so that the VGA box could switch between the two? I've seen people post about doing a mod to make the VGA permanently 15KHz, but how about a switch?

D · Post by D » Mon Aug 18, 2008 11:07 pm

My 2 sense?

The 15 Khz you are talking of would be 480i. Which just blows. Leave it be. Besides the question if it would be accepted by your designated screen device.
How many dc games are not 31Khz?
Those titles or better sequals were probably also ported to other systems.
want true lo res Bangai-Oh, get the n64 version, true 240p lo res.

Or I could be wrong about the whole thing, ask around.

zakk · Post by **zakk** » Tue Aug 19, 2008 12:01 am

Which VGA box do you have? There was one that actually had a 'hidden' 15khz RGB setting, although it came out of the standard VGA connector.

If yours is sort of a large-ish black box with a switch on the side that is labeled PC and TV it's actually a three way switch and the middle position is 15khz RGB

dmauro · Post by **dmauro** » Tue Aug 19, 2008 12:12 am

I'm not sure what box I have, it's in a tangle of wires so I can't get at it easily, but it's white, and I'm pretty sure the switch only goes two ways.

D, I think Bangai-o run at 240p on the Dreamcast. Can anyone confirm this?

edit: I think this post answered my question actually. The first reply says you can add a switch to the wire to go from 15KHz to 31KHz.
http://forum.arcadecontrols.com/index.php?topic=82255.0
(I don't have that same VGA Box, but I imagine it works the same way)

Post by **Dave_K.** » Tue Aug 19, 2008 12:26 am

Any Dreamcast VGA box can be modded to output 15khz (or switchable between 15khz and 31khz) via the VGA port. This works beautifully with a Tri-Sync arcade monitor. All thats needed is a SPST mini toggle switch and some wire cutters (ok maybe some soldering too if you want to be a perfectionist

).

The mod is pretty much as iatneH described. I also wrote this FAQ on BYOAC back in the day (2002):
http://arcadecontrols.com/arcade_consol ... #dc2arcade

[Stupid note: you can get Bangai-o to run at 31khz by flipping the VGA switch on your DCVGA box about a few seconds after it starts booting (just before the Sega Logo screen appears). Only probably is the cut scenes are totally screwed up. I think the game screen may not be full size either. Probably best in lowres anyway.

]

GaijinPunch · Post by **GaijinPunch** » Tue Aug 19, 2008 3:03 am

D wrote:My 2 sense?

The 15 Khz you are talking of would be 480i.

No it's not. Bangaioh supports 240p.

This works beautifully with a Tri-Sync arcade monitor.

This is what I have. I have a custom job made by the RGB Hospice (too bad he's not around). It's generally a homemade box, with an AV-Multi (RGB) output. I've gotten 240p & 480p out of it, but for the life of me can't remember what the hell I had to do. Won't the games (to an extent) detect what's available and default to one?

dmauro · Post by **dmauro** » Tue Aug 19, 2008 3:05 am

I would rather play it in 15KHz definitely. Thanks for the tips!

GaijinPunch · Post by **GaijinPunch** » Tue Aug 19, 2008 3:07 am

This is what I have:
http://dempa.jp/rgb/drug/dcava01dx.html

It has a toggle, as pictured.

D · Post by D » Tue Aug 19, 2008 6:38 am

wtf?
Dreamcast can suddenly do 240p?
huh?
Which games?
Sorry for the misinfo, I only know what I know.

EDIT:
Oh yeah, SFIII TS has this video option right?
What other Dreamcast games run @ 240p?
Emulators perhaps.

rtw · Post by **rtw** » Tue Aug 19, 2008 6:57 am

iatneH wrote:A simple SCART cable ending in a VGA connector should work.

Not recommended, the SCART output voltage is a lot highter than the VGA output voltage. You would most likely saturate the image.

rtw

Post by **Dave_K.** » Tue Aug 19, 2008 5:35 pm

dmauro · Post by **dmauro** » Tue Aug 19, 2008 7:22 pm

Yeah, thanks a lot for all the links and pictures. This is all very helpful. I'm going to dig my VGA adapter out of the tangle of wires so that I can open it up and examine it, but I imagine I'll even be able to wire the thing up so that the switch that's already in the case can go between 31KHz and 15KHz rather than VGA and composite.

Post by **Dave_K.** » Tue Aug 19, 2008 8:05 pm

D wrote: What other Dreamcast games run @ 240p?

Not many, or at least none of the Naomi ports.

dmauro wrote:I imagine I'll even be able to wire the thing up so that the switch that's already in the case can go between 31KHz and 15KHz rather than VGA and composite.

Not a bad idea, but be aware some games don't even support RGB so you would simply get a blank screen. I think the SFIIX and Vampire Chronicle fighter games are two examples of this. Probably not any games you would play anyway. You also would not be able to force games into VGA (that don't normally support it) using the switch trick mentioned above.

Endymion · Post by **Endymion** » Fri Aug 22, 2008 4:26 pm

GaijinPunch wrote:This is what I have:
http://dempa.jp/rgb/drug/dcava01dx.html

It has a toggle, as pictured.

This box actually has two dipswitches. The VGA is turned on with both are closed (pin 6 & 7) and traditionally, VGA boxes turn off the VGA mode by simply opening pin 6. With two switches it's possible to open up pin 7 and leave pin 6 closed. I have been trying to find out for years just what this might be useful for. Have you found any games that function with one switch closed and not the other? Or any different effects with any games? I'm thinking I am just going to have to mod a box and start going down a list of titles to see what happens.

dmauro · Post by **dmauro** » Wed Dec 17, 2008 4:59 am

I got this up and running on my cabs with a 15/31 switch. I'm going to post a rundown of how I did it on arcadeotaku and I'll link it here, but the short of it is a) Bangai-O looks fantastic in 240p b) Naomi games look shit in 480i and c) I can't even get video on Third Strike in 15KHz. I thought I had heard that 3S could be forced to 240p, but maybe it's because I'm using the Toodles Capcom Fighter Collection disc?

Oh and I accidentally destroyed my first VGA box in doing this somehow. It was a crappier one that actually connected pins 6 and 7 immediately in the cable rather than in the box, and in the process of figuring that out I must have done something to ruin it. The new VGA box I got makes things much easier, and since it's the VGA box that seems to be very popular, showing how to add a switch for that one will probably be more helpful for others.

Blinx123 · Post by **Blinx123** » Wed Dec 17, 2008 5:09 am

Isn't there a bootlader disc around that is capable of forcing nearly any game into VGA mode? I think it was the CD-X one, made by Datel.

dmauro · Post by **dmauro** » Wed Dec 17, 2008 5:17 am

Yeah, almost every game can be forced into VGA mode, but it's very tricky to force Bangai-O and then you'll get graphical glitches, and the game is native 320x240 anyways, and I was hoping I would be able to run 3S on my low-res monitor. I think I saw something about holding Y+Start during boot, so I'll try that out.

dmauro · Post by **dmauro** » Wed Dec 17, 2008 5:07 pm

Guide is up at the ArcadeOtaku forums.

brokenhalo · Post by **brokenhalo** » Thu Dec 18, 2008 6:32 pm

At the Capcom logo, hold L + Start to switch to a low resolution mode. To switch back to high resolution interlaced mode, hold Start + X at the Capcom logo.

^^^stolen from neoseeker.

dmauro · Post by **dmauro** » Thu Dec 18, 2008 6:53 pm

Awesome, thanks! Still very curious that I'm getting a dark screen in 15KHz though. Hopefully that trick will fix it though.

dmauro · Post by **dmauro** » Mon Jan 12, 2009 5:10 pm

I can't seem to run Third Strike in 15KHz via VGA without simply getting a black screen.
edit: someone else seems to have had the same problem, but there is no solution there.

edit: AHA!

A patch is just a small part of code that is replaced by another in order to change some features in a program. In your case, you need a RGB fix because some DC games have some kind of protections against european DC so that if you play with a RGB cable, you'll get a black screen or your game will reboot.

My Dreamcast is PAL, so I need to patch the disc.