Ben1l

macrumors regular
Original poster
Nov 30, 2006
236
2
I have a Mac Pro 2013 (trash can) with 2 x D500 graphics cards.

I currently have two Dell HD monitors connected to the Mac Pro via an DVI to Thunderbolt adapters. I'd like to connect a third monitor in the same configuration or by it's HDMI port direct to the Macs HDMI port.

I can only seem to get two of the three monitors working at any one time!

Any ideas about what I'm doing wrong?

Thanks,
Ben
 

Fl0r!an

macrumors 6502a
Aug 14, 2007
909
530
Pretty sure you need an active DisplayPort adapter (or a native DP connection) for the 3rd and following displays. Those AMD cards support only 2 legacy connections (DVI, HDMI) at a time.
 
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Ben1l

macrumors regular
Original poster
Nov 30, 2006
236
2
Pretty sure you need an active DisplayPort adapter (or a native DP connection) for the 3rd and following displays. Those AMD cards support only 2 legacy connections (DVI, HDMI) at a time.
Thanks, I had a quick look on the Apple store website for one of those cables. They seem to be around £85. That seems like a crazy amount of cash for a converter. Seems utterly bizarre that this mac pro can support 3x 4k displays and only 2x HD displays!!
 
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netkas

macrumors 65816
Oct 2, 2007
1,179
336
Thanks, I had a quick look on the Apple store website for one of those cables. They seem to be around £85. That seems like a crazy amount of cash for a converter. Seems utterly bizarre that this mac pro can support 3x 4k displays and only 2x HD displays!!
In trashCan only one videocard (of two) handles displays. SO yeah, you are limited to 2 legacy connections.
iirc, newer cards, like R9 290/285 supports more than two legacy connections, so one can connect two dvi and one hdmi screen to R9 290. But D500 is just too old for that.

And you don't need to buy mdp->dvi adapter from apple. Any ACTIVE adapter should work.
 
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Ben1l

macrumors regular
Original poster
Nov 30, 2006
236
2
In trashCan only one videocard (of two) handles displays. SO yeah, you are limited to 2 legacy connections.
iirc, newer cards, like R9 290/285 supports more than two legacy connections, so one can connect two dvi and one hdmi screen to R9 290. But D500 is just too old for that.

And you don't need to buy mdp->dvi adapter from apple. Any ACTIVE adapter should work.

Thanks for the explainer, I think the "legacy connections" bit might be a littler over my head technically, but appreciate that that is the bottleneck...

Would be really grateful of you could send me a link to the non apple version of the adapter you mentioned on Amazon or similar.
 
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Fl0r!an

macrumors 6502a
Aug 14, 2007
909
530
Just do a search for "active mini displayport adapter" on ebay or amazon, any of those should work.

Personally I own this one. Note that it has a fullsize DP conncetor, so it won't physically fit into your MacPro. You need the same one with a miniDP.
 
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MacVidCards

Suspended
Nov 17, 2008
6,096
1,054
Hollywood, CA
Good idea, but a real one where you choose the GPU and outputs.

Or pay attention to specs.

Your call.

It has GPUs that only support 2 older displays.

I frequently find our customers don't realize that their display could use DP by just spending $15 on a cable vs sticking with DVI and needing an $85 active adapter.

Do some research and you will find active adapters or that your displays have DP input in the first place.
 
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ActionableMango

macrumors G3
Sep 21, 2010
9,606
6,867
Thanks for the explainer, I think the "legacy connections" bit might be a littler over my head technically, but appreciate that that is the bottleneck...

Would be really grateful of you could send me a link to the non apple version of the adapter you mentioned on Amazon or similar.

I barely know what I'm talking about here, but legacy connections are those prior to DisplayPort. For example, VGA DVI HDMI. Legacy connections require an additional hardware clock on the video card, per legacy connection. The AMD card you have in the nMP has two of these clocks, therefore you can support two legacy connections. For three or more monitors, two can be legacy and the rest will have to be DisplayPort (or Thunderbolt). The second AMD card in the nMP is compute-only and therefore has no output connectors.

A passive adapter doesn't have this clock. So while it can convert the physical connector from DisplayPort/Thunderbolt on your nMP to DVI, it relies on a clock on the card. That's why you're stuck at two monitors with passive adapters and/or legacy connections.

An active adapter does have this clock. This makes it more expensive than a passive adapter. Every monitor with a legacy connection, after the first two, will require an active adapter.

What MVC is saying is that a lot of his clients stick with HDMI or DVI because that's what they know and then they end up trying to adapt that, when in fact there's actually a DisplayPort on the monitor and they should have just used that in the first place.

As a former desktop support guy, and still the support guy for everyone in my family, I have frequently seen people use the worst possible connection to their monitor because they just want to use the same cable they've been using forever.
 
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