Running three Monitors off a Radeon 5870 card

Okay, as said last time, I bought a Radeon 5870 card with the desire to drive three monitors. Now, ATI proudly claims that they have three independent display controllers, which is true. And the card has 2x DVI, 1x HDMI and 1x Display Port, so you would expect a setup of 2x DVI and 1x HDMI to work, right?

Wrong. You see, DVI/HDMI and DisplayPort have different Signal Types. DVI and HDMI use TDMS, while Display Port uses a completely different protocol. And guess what? The card only supports up to two TDMS Signals, which means 1x DVI and 1x HDMI or 2x DVI, but not 2x DVI and 1x HDMI as that would require three TDMS outputs.

Now, the solution seems easy, just get one of those cheap $10 DisplayPort > HDMI or DVI adapters, right? Wrong again. Those adapters do not convert the signal, they seem only able to mechanically convert and then require the host to generate a TDMS Signal. You need an "active" Adapter, that is an adapter that actually converts the signal. Those require extra power, usually provided through an USB Port. And they are expensive.

I bought one from Dell (R478G), which set me back a hundred bucks. Other adapters are sold by Sapphire or Accell and possibly others, but they are all around that price range. Sadly, I already had three Monitors at that point, otherwise I would recommend paying the extra money for a DisplayPort Monitor as the Adapter can cause problems (check the reviews) or even considering a second graphics card, which kinda defeats the purpose of getting a Radeon 5xxx in the first place.

Oh well, at least I now finally have three monitors for a 6016 Pixel wide screen...

Comments (3)

David WelchJune 6th, 2011 at 17:38

That was useful. I have two display screens running on a HD5570, using the HDMI and VGA ports, and I was wondering if I could use the additional DVI port to connect a third screen.

From the above article it is not worth trying to connect a third screen 🙁

Serge LaRondelleMay 31st, 2012 at 07:48

Wow. Thanks for that write up! Very helpful, unfortunately I went out today thinking I was all smart and dropped the money on three new Asus monitors and a MSI Radeon HD 6870. I have spent the last couple hours trying to figure out why when I plugged in the HDMI I lost all screens. So after all my research it looks like I have three choices.
1. Return one monitor and purchase one with a displayport input.
2. Buy an active dongle like this one.
3. Buy a special display port to 3 dvi adapter.

I think I'm just going to return the monitor and pay extra for a monitor with more ports then just buying a patch for the problem. Thanks for your help!

mstumMay 31st, 2012 at 08:03

Definitely go for a DisplayPort Monitor! I bought one of the 100$ adapters, and this was the result:

Haven't tried the DP to 3 DVI one though.