The 28.xxxx crystal might drive CGa scan rates

And according to Per yes it can
http://www.vcfed.org/forum/showthread.php?197 … ow-res-CGA-mode

But no VGA in CGA mode

Beyond running through all the settings you could try to trace out the switches

From memory those things could drive mda and should do cga, I’ve never had one that was functional

Thanks!

The settings URL that Per referenced at the end of that thread is a dead link. But upon retrieving it with the Way Back machine, I saw that it's identical to another TVGA 8800CS card mentioned on Stason (https://stason.org/TULARC/pc/graphics-cards/U … -16-BIT-VE.html). This card is similar to mine, but it has 3 jumpers instead of 2. I tried those switch settings regardless, but still no luck.

Another thing worth mentioning perhaps, is the following:
- pin 7 is unused in the CGA standard and mode 1 EGA, AFAIK. But I actually had to physically disconnect it, because otherwise my 1084S-D1 produces a garbled image with my CGA card.
- I also pre-emptively disabled pin 2 (= second ground pin) because the two grounds on the 1084S-D1 are connected, which could short out an EGA card (as mentioned on Wikipedia's EGA page).
Not sure if this could have an effect.

What do you mean by tracing out the switches?

It would be beyond my skills for sure, but at least in theory, wouldn't it be possible to hack a CGA monitor to bypass the TTL logic, so it can take an RGB signal straight from a VGA card? Somewhere inside the monitor, the discrete logic in the monitor ends up converting the digital color information to analog RGB signals anyway, right? Yes, I know, there's the horizontal sync to take into account, and the the fact that it wouldn't support high resolution VGA, but 320x200 in 256 colors (as supported in most games) could be made to work with such a modification, right?

Yeah, I know, it's sacrilege to mod increasingly rare CGA monitors, I get that. But it can be done in a way that would leave the TTL compatibility in tact, right? Give it a 15-pin port right next to the existing 9-pin port (or fixed cable).

digger wrote on 2021-04-06, 23:11:

It would be beyond my skills for sure, but at least in theory, wouldn't it be possible to hack a CGA monitor to bypass the TTL logic,

Yeah, I know, it's sacrilege to mod increasingly rare CGA monitors, I get that. But it can be done in a way that would leave the TTL compatibility in tact, right? Give it a 15-pin port right next to the existing 9-pin port (or fixed cable).

It would be easier to mod the card to do 15khz vga scan rates with combined sync given his monitor is already RGBS analog compatible.

Some CGA analog screens already exist (like his)
mainly to support C64/Amiga and home micros
Most Magnavox and Phillips screens already support RGB analog along side ttl (CGa)

The trouble is they are 15khz and combined sync

In terms of modifying TTL to analog is that everything inside is different unless the screen was already designed to be easily configured for targa/analog which is just an adapter cable and a circuit to combine the HV syncs.

There is a very simple circuit that can up analog voltage to 8 color TTL but it is almost useless for anything but text.

https://www.repairfaq.org/sam/vidconv.htm

Modding would probably be overkill in my case 😀 I could pick up an EGA card that supports CGA monitors from Ebay. They are also not easy to find, but a lot easier than an EGA monitor. I know that Paradise, Prisma, ATI and others support it. In fact, my 8800CS card seems to be an exception in not supporting CGA monitors.

If anyone has an EGA card for sale, please ping me 😀

Regarding the modding option: the 1084S-D1 supports analog (e.g. for the Amiga). However you would need something like a scan "de-doubler" to go from 31Khz to 15Khz if you'd take in a VGA signal. Going from EGA to analog seems a lot harder.

This brings up a strange question

There are literally more 15khz RGBS Analog monitors in existence than all bog standard CGA and EGA screens combined

Why then didn’t Those moderately common multi standard VGA cards support RGB Analog?

I know for a fact RGB Analog is 100% compatible with everything VGA at half the refresh and pixel clock.

You could even display 640x480 @ 60i as I have a Futura 100 that does display that resolution in RGB analog on a Magnavox monitor.

Gotta wonder if any of them did have undocumented support .

Also gotta wonder if one couldn’t just swap crystals on a vga card and wire HV sync pins together to drive a commodore 1084 in its native 256,000 colors

Oh and an averkey will de-double vga for use on your screen just need a 15-9 pin converter