VOGONS


First post, by b_rros

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Hi, I got a new old PC, it is an old 486 with a DX2-66 processor, the case is filled with rust so I will have to deal with that. But right now I would like to know a little bit more about the graphics card, it's a Western Digital card (I didn't even know that WDC made graphics cards) with some kind of dip switches on the back, does anyone know what those switches are?

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Reply 2 of 8, by Old Thrashbarg

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Just a guess, but the switches are probably for toggling between NTSC/PAL video mode. It could be that an RCA CVBS output is on those pin headers.

That's... not even anywhere in the ballpark.

The switches are for setting the refresh rates for the various resolutions. The pin header is just a regular VESA feature connector. Here is a complete description of the various settings.

Reply 3 of 8, by Stiletto

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Old Thrashbarg wrote:

Just a guess, but the switches are probably for toggling between NTSC/PAL video mode. It could be that an RCA CVBS output is on those pin headers.

That's... not even anywhere in the ballpark.

The switches are for setting the refresh rates for the various resolutions. The pin header is just a regular VESA feature connector. Here is a complete description of the various settings.

And here is the datasheet for the WD90C31A video controller (well, the WD90C31):
http://www.vgamuseum.info/images/stories/doc/wd/wd90c31.pdf

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Stiletto

Reply 5 of 8, by keropi

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Auzner wrote:

Then I actually was in the ballpark, since NTSC and PAL are different refresh rates.

Not really, there is also different color encoding, timing , blah blah blah. PAL/NTSC is not just a 50/60hz difference. But that's not for discussion here...

The switches are indeed for selecting refresh rates in higher resolutions as well as selecting to have them interlaced.
What is interesting is the fact that there are 2 WD chips on this VGA, what do they write on them? One is the WD90C31A and the other? It could be a case that one is an accelerator for high-res stuff

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Reply 7 of 8, by Old Thrashbarg

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That second chip is probably just for the VLB interface... IIRC, the 90C31 didn't natively support local bus.

The 90c31 was an 'all-in-one' chip with both standard VGA and acceleration functions built-in, similar to the ET4000w32 and Cirrus 542x series. It was a pretty decent performer for its time too, so it wouldn't have needed a second accelerator chip.