VOGONS


First post, by mpe

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Going through my VGA collection I keep thinking about the VGA feature connector.

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It seem so widespread on contemporary VGA cards. I am yet to see a pre-AGP card without one.

On the other hand, I've hardly seen any devices that connected to this connector.

It sound like a goo concept but even obvious choices like early MPEG accelerators or some other devices used different way of integration. Either external pass through or proprietary ports. Was it not suitable for 3Dfx or other things for some reason? Was it bandwidth or compatibility that limited its use?

Do you own any devices connecting to the feature connector? If so could you show them?

Last edited by mpe on 2020-04-12, 12:47. Edited 1 time in total.

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Reply 1 of 17, by derSammler

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Early VR headsets used it, as well as some companion cards for graphics acceleration. I think the 3DO Blaster needed it as well.

There were some MPEG decoder cards for it too, but most companies made their own proprietary MPEG decoder add-ons, so they could make additional money.

Reply 2 of 17, by Tiido

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That connector is supposed to only support paletted 256 color modes which limited its usefulness a lot.

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Reply 4 of 17, by Tiido

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That article doesn't give any actual information. All that I have found has suggested that only the advanced feature connector can do high resolutions with high color depths but it is a completely different beast with many more pins to accomodate 24bit video.
The normal feature connector has only 8bits of pixel data that connects straight to palette input of a RAMDAC, when normal input gets disabled. I haven't been able to find any actual usage and programming info though, just pinouts.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 7 of 17, by vlask

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Got this one, like that cable has dual version connector, for old as well as new one.....
http://vgamuseum.info/images/vlask/avance/alg … wgfcreative.jpg

Not only mine graphics cards collection at http://www.vgamuseum.info

Reply 8 of 17, by mpe

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Yes. Video Blaster ISA.

There were several standards. EGA and then VGA. I believe the VGA edge is compatible to the 26pin one.

Datasheets mention 80-pin VAFC (VESA Advanced Feature Connector) with 16bit interface but none of my cards has one.

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Reply 9 of 17, by yawetaG

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vlask wrote on 2020-04-13, 14:41:

Got this one, like that cable has dual version connector, for old as well as new one.....
http://vgamuseum.info/images/vlask/avance/alg … wgfcreative.jpg

Why does the cable have an additional connector?

Reply 12 of 17, by vlask

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yawetaG wrote on 2020-04-16, 06:05:
vlask wrote on 2020-04-13, 14:41:

Got this one, like that cable has dual version connector, for old as well as new one.....
http://vgamuseum.info/images/vlask/avance/alg … wgfcreative.jpg

Why does the cable have an additional connector?

Because you can choose between new interface (connected one, 2 row of pins on card) or old interface used on older ISA cards. Old one looks like this.
http://vgamuseum.info/images/pepino/ati/ati_2 … _basic-16_f.jpg

Not only mine graphics cards collection at http://www.vgamuseum.info

Reply 13 of 17, by rasz_pl

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There were a few Vesa to very old LCD projects around 2003-5, main one was probably at tweakers.net
https://web.archive.org/web/20071219202302/ht … messages/799377

all I could find on todays web is this with 2 somewhat detailed PDFs, one in German, other Polish:

https://www.maltepoeggel.de/?site=tft2pc&p=3&lang=de

TLDR: 8 bit only bus so sending indexes direct to ramdac. I guess You were supposed to snoop on the ISA bus for the VGA palette register writes. Problematic with parallel RGB screens, 16 color modes can be made to work ok. Problems with clock frequencies - shifted screens, losing sync in some modes. I dont think anyone bothered to play with reprogramming VGA CRTC at the time. Strange considering it wasnt black magic, there were already DOS programs reprogramming VGA into 15KHz mode for SCART RGB operation as early as ~1996. I used TV as main VGA screen with scart cable for over a year on my first PC. Dos text modes, DOOM, UFO, Privateer, Colonization all ran fine with reprogrammed clocks.

Reply 14 of 17, by appiah4

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I have a Dell XPS D333, it is the top of the time model that shipped with a DVD-ROM in late 1997 and it came with a Riva128 AGP that is connected to a DVD/MPEG2 Decoder PCI card via the Feature connector header. Amazingly cool system.

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Reply 15 of 17, by furan

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rasz_pl wrote on 2020-04-29, 12:04:
There were a few Vesa to very old LCD projects around 2003-5, main one was probably at tweakers.net https://web.archive.org/web/ […]
Show full quote

There were a few Vesa to very old LCD projects around 2003-5, main one was probably at tweakers.net
https://web.archive.org/web/20071219202302/ht … messages/799377

all I could find on todays web is this with 2 somewhat detailed PDFs, one in German, other Polish:

https://www.maltepoeggel.de/?site=tft2pc&p=3&lang=de

TLDR: 8 bit only bus so sending indexes direct to ramdac. I guess You were supposed to snoop on the ISA bus for the VGA palette register writes. Problematic with parallel RGB screens, 16 color modes can be made to work ok. Problems with clock frequencies - shifted screens, losing sync in some modes. I dont think anyone bothered to play with reprogramming VGA CRTC at the time. Strange considering it wasnt black magic, there were already DOS programs reprogramming VGA into 15KHz mode for SCART RGB operation as early as ~1996. I used TV as main VGA screen with scart cable for over a year on my first PC. Dos text modes, DOOM, UFO, Privateer, Colonization all ran fine with reprogrammed clocks.

Things don't always work the way we expect. Pixel Data Bus is 8 bit yes, and in 8 bit mode, it is an index into the palette LUT on the DAC. In higher bit depths, it clocks out 8 bits of the color at a time. I wondered how I could use 16 bit color with the 3DO Blaster and took a look in depth with a logic analyzer - this is how. It is using the pixel data bus pins, and when not in palette mode, it is just sending 8 bits of the current pixel per pixel clock, sequentially. More interesting to me was finding that this was the design of several RAMDACs with full color support as well - they had an 8 bit pixel data bus, and only 8 bits at a time were sent, even for 24bpp - 3 clocks per 1 24 bit pixel.

I've been thinking about doing a video about all of the different modes of the VFC because folks keep getting it wrong. Yes, VAFC had a wider pixel data bus later, but it was not required.

Reply 17 of 17, by majestyk

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mpe wrote on 2020-04-14, 09:24:

Yes. Video Blaster ISA.

There were several standards. EGA and then VGA. I believe the VGA edge is compatible to the 26pin one.

Datasheets mention 80-pin VAFC (VESA Advanced Feature Connector) with 16bit interface but none of my cards has one.

Here´s an example of an 80-pin VAFC connector on a FIC PSK-2000 mainboard with S3 onboard graphics:

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Looks a bit like the common 80-pin SCSI connector.