Which VGA to RGB converter?

[keropi]

Hello!

In an attempt to save space on my desk I had the idea of connecting my DOS PC to a Commodore 1084 monitor I use for my amiga/consoles. The 1084 needs 15khz R-G-B and C-Sync signals to display an image.
The PC will output the standard VGA resolutions like 320x200/70hz , 640x480/60hz and everything that is typically used in DOS/gaming and displays fine in crt/lcd monitors.

I see on eBay there are plenty cheap Extron converters that I think do what I need, like the Extron RGB 109xi / RGB 118 / RGB 150xi / RGB 192 ones. Anyone here has a recommendation?
Or maybe these devices are not suitable at all and introduce huge conversion lag or have other issues?

Thanks in advance for any help!

[Fudoh]

These interface are no converters. You want a scan converter that takes your 31khz signal and does output a 15khz signal instead. The main problem I see if the 70Hz refresh rate you get for most low-res DOS applications. Scan converters will convert this to a 60Hz signal. At the same time you get a 480i or 240p output signal which is problematic if you want a 200p source signal mapped to this output timing.

Overall not the best plan.

[keropi]

I was kind of hoping you'd reply Fudoh and I am glad you did.
So what should I look for? Is there a solution for this reverse problem other than finding a dual-sync monitor or keep my current setup? I did google but couldn't find anything definitive, I did stumble on this page that made me look for the Extrons I mentioned: http://retrorgb.com/emotia.html - problem is that it says "vga 640x480" and not 320x200 ... I should have known it wasn't gonna be that easy

[Fudoh]

These are your options: http://scanlines.hazard-city.de/

The Emotias will take both 640x480p60 and 640x400p70 (which is the timing you get when you're displaying 320x200 MCGA/VGA games), but your 70Hz input will get converted to 60Hz. You'll lose smooth scrolling compared to a CRT actually running at 70Hz.

[keropi]

thanks Fudoh, I have some reading to do now that I have a direction.

[mikejmoffitt]

I have an Extron VSC-100, which is fine if you are okay with 480i output. Let me know if you want it.

[keropi]

thanks, still considering my options at this point - not a huge fan of 70->60hz conversion

[werk91]

Does your Commodore 1084 have RGB scart connection ? Maybe a UMSA Scart Adapter can do the job ?

[keropi]

I have created a female scart adapter cable for the 1084s , it was just a matter of making the right connections.
UMSA won't work for me, the problem I have is that the 1084 is a 15khz device and vga is 31khz... UMSA doesn't do any conversion so I won't get a usable image on the 1084

[werk91]

For some reason I thought the UMSA converts 31khz VGA to 15khz Scart

[yxkalle]

Are you guys sure a 1084 can't display a 15KHz 200p signal? Mine can do both 288p @ 50Hz and 240p @ 60Hz.

[Fudoh]

Are you guys sure a 1084 can't display a 15KHz 200p signal?

where would you get a 200p 15khz signal ?

[yxkalle]

Are you guys sure a 1084 can't display a 15KHz 200p signal?

where would you get a 200p 15khz signal ?

From a PC running in 320x200 (CGA?) resolution, I think.

[Fudoh]

Usually you're using a VGA card, so you get 640x400p70 instead for 320x200 games.

[keropi]

yep I wrote in the 1st post that I am interested in displaying vga signal to the 1084 , cga is no problem because it's one of the 1084s that have ananog and ttl rgb so cga just works on it. I use it for my XT-class machine that has an ibm cga installed, works great without any extra converters.

Since there is no easy/available way to display on the 1084 low-res 70hz vga stuff I am abandoning the idea... thank you all for contributing and helping in the thread , really appreciate it

[Fudoh]

Since there is no easy/available way to display on the 1084 low-res 70hz vga stuff I am abandoning the idea

only recently we a similar thread in which a few software solutions for DOS were discussed. This heavily depends on VGA chipset though, but might be an alternative - at least for some of the software you're using. Can't offer a link right now, but maybe you can find it.

[NightSprinter]

Fudoh: I've been trying this regularly on my Win98 computer feverently (as I'm trying to livestream DOS games from real hardware). It's nowhere near as simple as it sounds. Most games that uses Mode13h or the default Mode-X timings are fine. Some (like the pinball games from DICE in low-res mode) might display at 30Hz (at least, for cards that don't do interlace) on 350-line modes, have screen cut-off (main menu of Jazz Jackrabbit, or all of Turrican II), or even start displaying at horizontal scan rates the display can't handle (Pac-PC II and Ms. Pac-PC in Full-Screen mode, Epic Pinball and Jazz Jackrabbit in-game, all of Supercars International or many VESA modes up to 480p60). It didn't matter which utility I used (either VGATV for ATI Mach64-based cards or S3, AdvanceCab's utilities for numerous supported cards, or Mon-Arc Plus for my Voodoo3), as I always had to deal with some form of incompatibility with the various games I have.

This was all tested on my NEC XM2960, which for low-res can unofficially handle Extended Resolution up to 16.5KHz. So I hate to say this, given how differently some DOS games work, even an Emotia might not always work depending on the game. I don't even know how it would handle EGA-resolution games, given those went up to 640x350p.