Dual monitors, dual link DVI, et al.

Headcase_Fargone

Limp Gawd
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I've been running two 1080p monitors for a while now, both with separate DVI-D cables connected to one of two Crossfired Radeon 6970s. I recently picked up one of the Qnix 1440p displays which comes with a dual link cable and I can't seem to make it work with another monitor.

The Qnix only works on one of the two ports on this video card. If I plug it into the other I get no signal. Plugging it into the "correct" port I get a signal and everything works fine so long as the Qnix is the only monitor plugged in. If I attempt to plug a second monitor into the other DVI port on that same video card with a DVI-D cable THAT monitor will then get a signal but the Qnix loses its.

What do I need to make these monitors work together?
 

falkenbd

Limp Gawd
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Dec 11, 2013
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The 1080p monitors really only use DVI - so they don't utilize DVI-D. The Qnix does, so its not able to have another on the other DVI if you utilize DVI-D.

Does the video card have HDMI or display port? I'd check the manual of the graphics card to be certain, but it probably says you can't use DVI-D and DVI together.

In my situation, I had to get an active display port adapter
 

falkenbd

Limp Gawd
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Ack, I was afraid of that. It does have DP ports, yes. Aren't those adapters really expensive?

Check your manual to see which ports you can use simultaneously first.

Maybe you can get by with HDMI->DVI or something. If you need DP adapters, check monoprice - passive isn't too expensive, but I'm not sure what you'll need.

I got an active adapter on monoprice for $15.
 

Headcase_Fargone

Limp Gawd
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I looked up the cards I'm running and they're actually 6950s. I unlocked them to run as 6970s, but that's neither here nor there.

So according to the HIS site they have one dual link and one single link DVI port, as well as an HDMI and two mini DisplayPorts. The manual states that these cards support up to six monitors through any number of port combinations, including "native" on both DVI connectors.

So what am I doing wrong here?
 

falkenbd

Limp Gawd
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I think basically your DVI-D (dual link) uses up both DVI ports when you are running >1080p

native on both DVI probably doesn't account for the 1440p resolution.

Same thing happened on my 7950. You need to use the HDMI or mini display ports for one of the monitors. (1440 is only supported by dual link dvi or DP)
 

Headcase_Fargone

Limp Gawd
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So displayport adapter it is then. Any difference between active and passive for this purpose? Recommendations for a decent one?
 

kasakka

2[H]4U
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So displayport adapter it is then. Any difference between active and passive for this purpose? Recommendations for a decent one?

I believe you need active for DP -> dual link DVI. A better solution would be to hook up your second monitor via Displayport, then you can use a much cheaper passive adapter if your second display is only 1080p.
 

TESLA

Gawd
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Just to clarify some language...

DVI-D = Digital pins only
DVI-I = Analog and digital pins
DVI-A = Analog pins only

Any variant of DVI which carries a digital signal (be it DVI-D or DVI-I) may have a single set of digital pins (single link) or two sets of digital pins (dual link):

Single link DVI-D
Single link DVI-I
Dual link DVI-D
Dual link DVI-I
DVI-A

Anyway, the 6950/70 has a connection layout as follows:
Upper single link DVI-D shared with HDMI (you cannot use both at the same time)
Lower dual link DVI-I (only dual link if this is the only DVI or HDMI connection, otherwise this is a single link connection)
2x mDP (two total displays)

In other words, for the upper and lower DVI ports and the HDMI port, connection options are limited to:

One single OR dual link monitor connected to the lower DVI port
OR
One analog monitor connected to the lower DVI port
OR
Two single link monitors connected to the HDMI and lower DVI ports
OR
Two single link monitors connected to the upper and lower DVI ports
OR
One analog monitor connected to the lower DVI port and one single link monitor connected to the upper DVI port
OR
One analog monitor connected to the lower DVI port and one single link monitor connected to the HDMI port

Those are your possible combinations for these three ports.

As for the two mini DisplayPort ports, I believe these are dual-mode ports, so they will support passive mDP to single link DVI cables (and passive mDP to HDMI adapters although I did not confirm audio support). But mDP to dual link DVI cables would need to be active.

If using native mDP or DP monitors, then you need not worry about single link versus dual link. DisplayPort's bandwidth exceeds that of even dual link DVI.

As such, you can use as many as four displays with this particular card. Up to two single link displays may be connected to the DVI/HDMI ports, and up to two displays may be connected to the mDP ports (limited to single link displays if using passive adapters).

Hope this helps.
 
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Headcase_Fargone

Limp Gawd
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Very informative, yes. Would you recommend what the above poster said in regards to a passive DVI to DP adapter for the second (1080 only) monitor? It only has DVI input as well, like the Qnix.
 

falkenbd

Limp Gawd
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So displayport adapter it is then. Any difference between active and passive for this purpose? Recommendations for a decent one?

I recommend monoprice active. Works well for my 1440 monitor.

You should be able to use that, and then hook up 1-2 other DVI (1080p) monitors then.

I'm not 100% sure but I think a passive would work only for 1080p (which i guess you could use on your 2nd monitor)
 
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Headcase_Fargone

Limp Gawd
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I recommend monoprice active. Works well for my 1440 monitor.

You should be able to use that, and then hook up 1-2 other DVI (1080p) monitors then.

I'm not 100% sure but I think a passive would work only for 1080p

Was it this one? It's out of stock and has some bad reviews stating it doesn't support over 1200.
 

TESLA

Gawd
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Yes to using the mDP to DVI adapter, but I checked again and I do not believe the mini DisplayPort outputs to be dual-mode. (I initially thought they would be.)

Anyway, still use the adapter, but just make sure that it is active. A passive adapter will not work without dual-mode support.
 

falkenbd

Limp Gawd
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Was it this one? It's out of stock and has some bad reviews stating it doesn't support over 1200.

Link is blocked for me (ads) but if its PID 9425 then it is.

Not sure why I didn't have those issues but some people seemed to. I can't recommend a different one as this is the only one I've used.
 

TESLA

Gawd
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Was it this one? It's out of stock and has some bad reviews stating it doesn't support over 1200.

That is a single link adapter. Above 1920x1200 requires a dual link adapter. These are much more expensive, around $50-100, and do not work all that well.

Anyway, use the native dual link DVI port (lower DVI port) to connect your higher resolution monitor and use a mDP to (single link) DVI active adapter (the one you linked should be OK, the bad reviewers are from uninformed reviewers) for your older, lower resolution, monitor.

To connect two 2560x1440 or above monitors, at least one of the monitors must have native DisplayPort or you would need to purchase an (again, notably unreliable) dual link DVI active adapter.
 

Headcase_Fargone

Limp Gawd
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Link is blocked for me (ads) but if its PID 9425 then it is.

Not sure why I didn't have those issues but some people seemed to. I can't recommend a different one as this is the only one I've used.

That's the one. It appears to be DP to single DVI, not dual. At any rate, it's out of stock until May (!?). I'm actually having a hard time finding one that specifies it supports over 1200 resolutions. The ones on Amazon specifically say up to 1200.

Edit: After reading the rest of the recent posts I'll be taking Tesla's advice and using a DP to single DVI adapter for the smaller 1080p monitor. Thanks much everyone, learned a lot about DVI today.
 

falkenbd

Limp Gawd
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I will have to look at my setup again. I must be mistaken on how I was using that.

Yes, you should use the adapter on the lower res monitor, dvi-d on the 1440
 
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