PCI express for board-to-board link.

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The discussion focuses on interfacing two processing boards using PCI Express x8 with off-board 68-pin connectors from Molex, while addressing the challenge of matching these to the standard 98-pin edge connectors. Participants seek guidance on the standardization of the 68-pin connector and inquire about relevant documentation, noting that the PCI Express Card Electromechanical Specification lacks details on this connector type. Concerns about cable length, impedance control, terminations, and signal integrity are raised, with references to the PCI Express External Cabling specification, which is currently incomplete. Molex's website offers pinout descriptions and various cable lengths, but more comprehensive information on impedance control is needed. The conversation highlights the complexities involved in establishing a reliable board-to-board PCI Express connection.
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I want to interface two processing boards with PCI express x8 and connect them with cables. I find 68-pin off-board connectors for x8 connection (by molex) where as there're 98 pins for edge connectors. How do I match these 98 to 68? Are there some documents talking about this? I read PCI Express Card Electromechanical Specification, but there's only edge connector definition inside. Is this 68-pin connector also standard?
 
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fiedel said:
I want to interface two processing boards with PCI express x8 and connect them with cables. I find 68-pin off-board connectors for x8 connection (by molex) where as there're 98 pins for edge connectors. How do I match these 98 to 68? Are there some documents talking about this? I read PCI Express Card Electromechanical Specification, but there's only edge connector definition inside. Is this 68-pin connector also standard?

Does Molex have any application notes for that connector?

Beyond the electromechanical issues, how long are these cables? What is your plan for impedance control, terminations, and signal integrity?
 
Well, I see the pinout description on their website, for cable assemblies.

Molex provides several selection for cable length. Impedance control is another problem for me. I can only find such information for edge connectors. It must have been defined in PCI Express External Cabling specification. I can only find a draft of it, in which several chapters are missing...
 
I am trying to do the exact same thing. How did this work out for you?
 

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