Turning these video signals into VGA

[MattHollands]

I think I got the one with two VGAs, but its from ebay so can't be sure! Just gotta wait for delivery now.

[miguelvp]

If you want to fine tune it, you should download the documents from that "GBS 8200/8220 CFW Project",
He has a google drive with all kinds of datasheets and programming guides:

https://drive.google.com/folderview?id=0B9y2RH4Lb3MZLUYtWGFOMUFVdlE&usp=sharing

[miguelvp]

Well, after reading the documentation and all that jazz and since I do have several retro game consoles I did a search and found the dual header (GBS-8220) at Amazon, so I got one that should be here in a couple of days (no I didn't pay extra, actually free shipping because my wife is an Amazon Prime member).

It's pretty cheap in there so I just couldn't help myself:
http://www.amazon.com/Andoer-Portable-GBS-8220-Definition-Converter/dp/B00XKWX0SY

Sorry I didn't find this before hand.

The reason I did get it is because if you look closely on the chip, it does have digital input OR output (not both) for maybe doing HDMI out as well since VGA on TVs are pretty much phasing out and the composite video from game consoles do suck a lot.

If I get mine before yours I'll see if it works with my repro signal.
One thing I did find on video reviews etc is that the menu usually defaults to Chinese. If that is the case for you, press the Menu button and select option 4, that's the language selection and you should see English on that submenu as option 1.

Also by looking at the input voltages you might not need to alter the output voltage at all, specially since they have pots to adjust the level for all red green an blue channels which you probably want to drive all three with your video signal and adjust them to get your preferred foreground color.

[miguelvp]

Well, gotta love Amazon, got my board already.

Good news/Bad news.

Bad news is that out of the box applying the signal similar to yours I can't get it to lock.

Good news, well not that good, is that I can see something on the screen.

I think it's because for the 25KHz signal it needs to use the RGBS, meaning that the HSync and VSync have to be combined.
Also since there is plenty of documentation maybe we can coerce the video processor (TVIA TrueView 5725) to work with your signal since we have access to all that documentation on that google drive.

Since I can reproduce your signal and I have the board I can keep on helping but I hope I didn't make you waste ~$30 and sorry if you paid more.

[Ian.M]

The first thing I'd try would be XORing the H and V sync signals to get what should closely resemble a correct C sync signal.   As they don't go all the way to 5V, use 74HCT or real TTL.  One gate from a 74HCT86 or 74LS86 should do the job.

[MattHollands]

Hmm mine still hasn't arrived! That's annoying. No worries, I'm sure we will figure out a way to get this to work.

I'll check my components to see if I have any HCT or LS series. I feel like I won't because I'm studying abroad for the year so don't have all of my kit with me 

[Ian.M]

An XOR can be built from four NAND gates, so you could also use all the gates of a 74LS00 or 74HCT00.


Other 'flavours' of CMOS logic would probably work, but your sync pulse high level is only about 4V which is a bit marginal for a logic '1' in most families if powered from 5V.

[miguelvp]

This link I think it will be of use, posting it here for future reference:
https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-vga

Look at the combined sync section.

[Ian.M]

@miguel:  *EXCELLENT* find!

[MattHollands]

My board came today! Turns out it's the version with only one vga output. I'll try to find some time in the next couple of days to experiment.

Also by looking at the input voltages you might not need to alter the output voltage at all, specially since they have pots to adjust the level for all red green an blue channels which you probably want to drive all three with your video signal and adjust them to get your preferred foreground color.

Sorry for being slow. How can I find whether or not the voltages need adjusting?

[miguelvp]

It's ok, I'm taking a trip to Spain in a couple of days and I won't be back for over a week after that. I'll take my tablet but I won't be able to look at this for another two weeks.

But I'll keep my eye on the thread.

[Tantratron]

This link I think it will be of use, posting it here for future reference:
https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-vga

Look at the combined sync section.

Does anybody has a copy or an update link ?
Thank you, Albert

[squadchannel]

Our waybackmachine!
https://web.archive.org/web/20220127084244/https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-vga