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PCIe on/off feature: different implementations?


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So, I've been breaking my head over the PCIe on/off feature implementations on the various boards. As far as I know, the PCIe on/off switch is implementated on three boards/series:


- Rampage III Extreme BE

- Evga X58 Classified 4-Way

- Evga Classified SR2

- Rampage IV Extreme (and later ROG boards)

- ASRock Z77 OC Formula

- MSI Z77 Mpower


Now, if I understand the ROG marketing about the PCIe debug correctly the purpose of the switches is two-fold:


- debug graphics cards

- prevent condensation from killing multi-vga setup


In very simple terms, there are two parts of the PCIe lane: the first (smallest) part is power, the other is data signal (see image below). I assume that, if the PCIe is completely disabled both the power and the data signal should be shut off, causing the graphics card to not work. If only the signal is cut off, the card is still powered on but the data is just not sent to the screen.




I'm trying to figure out if there's a different implementation of the PCIe enable/disable switch on the various boards out there. I tested the switch on the Z77 OC Formula and found something interesting. Here's the test:


- use vga that does not require external power (all power comes from PCIe slot)




- go in bios

- disable pcie => screen goes blank

- enable pcie => screen comes back up


Since the screen comes back up, I assume the pcie switch just cuts the data signal but not the power. When measuring the vgpu of the card, it stays the same when enabled and disabled, so I figure the assumption is correct. I don't have an ROG board at hand, but I was told the PCIe is completely shut off - both power and data signal.


Could someone who has all the boards do a test to verify? So:


- use vga without power connector

- go in bios

- enable/disable

- measure vgpu and check behavior


Wish I could do it myself :D



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I'm using am an Rampage III Black Edition and it can also switch off the PCIe. So the R3E is the first Asus Board that can do this, just an FYI ;)


On my Black Edition it's the following behavior, iirc (I tested it a long time ago):

If you turn of the PCIe Slot the cooler of the card stops working and the screen goes out, and it did not come back...

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