HD5470 mobile max screens?

[snowdog]

Hello,

Our office has moved and for a laugh I attached a 3rd monitor to my lappy on HDMI in my new office.

I can however, not get 3 screens to work, does this piece of rubbish not support 3 screens? 2x1920x1080 (1x mon over hdmi 1x mon over vga) works fine, or laptop screen + either of the 2 extra screens, but not all 3. The moment I expand to screen 3, screen 2 greys out, and vice versa.

Is this a windows 10 (pro) limitation, a gpu limitation, a driver limitation ?

Just curious, atm I'm still working on my lappy as my PC is still in the old office, and for PC I'll be using 2 not 3 screens anyhow. But some day I might want a 3rd...

 

[Confused Stu]

I think it's a GPU limitation you've run into there mate.

Any VGA, DVI or HDMI connected screen requires a clock signal from the GPU. AMD cards are fitted with 2 clock generators (except the Sapphire FLEX series, which have 3) which means they can support up to 2 VGA/DVI/HDMI connections. DisplayPort does not require a clock signal, which is why for 3 or more screens on an AMD card the third & above needs to be connected via DisplayPort to get all working at once.

AMD did manage to add a feature to the drivers when the R9 2xx series came out, whereby the card can share a clock generator between two screens provided they are identical screens and connected at boot up. This means if you have three identical monitors you can have 3 working using just DVI/DVI/HDMI or DVI/HDMI/HDMI, etc. I know from experience this worked on the 7970/280x cards, but I don't know if it worked with the HD5xxx series.

The problem I have is I don't know how your GPU sees the laptop screen. I am guessing it's not seeing it as a DisplayPort connection or you would be able to enable all three at the same time, so I'm guessing the laptop screen is needing a clock signal which only leaves one available for the external screen, which is why you can only enable 2 out of the 3 at any one time. Don't suppose the laptop has a DP/mDP output that you could use to connect the third? If so, an Active adapter to DVI/HDMI or VGA could be used to get the third screen up and working.

For desktops, there are often other options - I have 3 identical screens attached to my AMD GPU and a fourth, different one attached to the motherboard's Intel output - but laptops aren't generally customisable. There are USB3 to DVI/HDMI/VGA you could get if the laptop has a free USB3 and you need the third screen running, but they're not the cheapest at £50+ from a quick Google.

 

[snowdog]

Ah, thanks for replying dude

Yeah it's an old budget lappy from 2009 (upgraded though, from pentium P6100 to i5 460m, 4>8gb, and hdd chucked out the window for a fast ssd), .

I do have a 2nd gpu on cpu, but I think it's disabled as I have a dedicated HD5470 with it's own dedicated RAM...