Did some CGA cards have a two-RCA feature connector?

Discussion about old graphics cards, monitors and video related things.

Did some CGA cards have a two-RCA feature connector?

Postby keenerb » 2018-1-29 @ 14:28

I picked up this same card on Ebay for dirt cheap:

Image

Can't quite find this same model on totalhardware (or other web sites), although this is EXTREMELY close:

http://www.uncreativelabs.de/th99/v/E-H/52421.htm

It has two RCA-style connectors, but no other CGA card I can find has two RCA jacks on back panel. I typically associate those with EGA feature connector.

Is it possible it's an external light pen interface + composite out?
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Re: Did some CGA cards have a two-RCA feature connector?

Postby reenigne » 2018-1-30 @ 08:54

It's not EGA: 16kB of RAM, 6845 CRTC, a character ROM and discrete logic means its got to be CGA. The second RCA jack could be for a light pen but those usually had a button on them and also required power - the RCA jack doesn't have enough lines for that.

So, I'm going to suggest the second jack is for a second composite output. And indeed there does seem to be a second DAC (2N3904 transistor and some resistors) way over on the other side of the board. There is a third 2N3904 as well with some unpopulated resistors - not sure what that's for (a third, internal composite connector maybe?). I'm guessing this extra feature was added as a marketing point and because it was cheap and easy to do rather than because it was particularly useful, but perhaps some people had applications for driving multiple composite monitors from a single CGA card such as public information display screens in airports and railway stations.
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Re: Did some CGA cards have a two-RCA feature connector?

Postby derSammler » 2018-1-30 @ 09:45

The lower one is composite out, the upper one is connected to the feature connector, that's it. So yes, for a lightpen option, for example.
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Re: Did some CGA cards have a two-RCA feature connector?

Postby keenerb » 2018-1-30 @ 14:04

Thanks. I figured as much after looking over the card more closely last night, seemed to be connected to the light pen interface.

I haven't seen many CGA cards with both connectors on the back, glad at least one might be composite output.
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