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ASUS Mobo and 6870 Crossfire Problems

Last response: in Motherboards
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August 2, 2011 4:24:16 AM

I have 2 new XFX Radeon HD 6870 graphics cards in my new ASUS P8P67-M Pro motherboard. They are in the first 2 PCIe x16 slots (navy blue and white) and are connected with a Crossfire bridge. My computer dual boots into both Windows 7 64-bit and Mac OS X Snow Leopard 1.6.8. In both Windows and OS X, both graphics cards are recognized as present in the system, but the first graphics card is running at x16 mode while the second is running at x1 mode. Catalyst Control Center (CCC) in Windows 7 recognizes the first graphics card as the "Primary Adapter" and the second card as the 'Disabled Adapter." 1 monitor is attached to the top DVI port of the first graphics card. When I attach a monitor to the second graphics card, it is not recognized and doesn't work. CCC doesn't show a crossfireX or crossfire tab or options.

I want to make my 2 graphics cards run in x8 and x8 mode in crossfire in Windows 7, and I want each to run 1 monitor in OS X. I noticed that there is an option for the third, black PCIe x16 slot (that I am not using) in the UEFI. When I turn that option to x4, the second graphics card isn't recognized at all (it doesn't appear in Hardware Manager). When I turn it to x2, it appears, but doesn't crossfire or support monitors (the situation I described above).

Please help my fix this problem. How do I force to motherboard to utilize each graphics card in x8 mode? In the motherboard manual it says that it it possible (and preferable) to do this. Why does the configuration of the third, unused PCIe x16 slot matter? Why does CCC not show crossfire options?

Thanks in advance for your help!

- Patrick
a b U Graphics card
a b V Motherboard
August 2, 2011 4:55:37 AM

It sounds like your board has defaulted into "dual 16x/1x mode", looking at the specs of the board it specifically says it will do both 8x/8x or 16x/1x. Have you looked in your BIOS for a PCI express setting? To be honest I'm not sure if your motherboard has that option in the BIOS but it may be worth a look. And of course you should read your motherboard manual if you have it, that my be the fastest and easiest way to fix your problem.


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