[SI-LIST] Re: Termination of unused PCIe pairs
- From: Joseph.Schachner@xxxxxxxxxx
- To: otter30 <otter30@xxxxxxxxxxxxx>
- Date: Wed, 8 Sep 2010 09:21:08 -0400
I should also say: PCIe transmitters do "receiver detection" - they look
for the 50 ohm impedance. So if you really are never going to use some of
the lanes from the card, there is no need to terminate them. Please pardon
me for not saying this in the previous email, I addressed the question ("do
I also need a .1u cap") and didn't address the point that you don't need
the termination resistors on unused lanes, either.
--- Joe S.
From: otter30 <otter30@xxxxxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Date: 09/07/2010 05:21 PM
Subject: [SI-LIST] Termination of unused PCIe pairs
Sent by: si-list-bounce@xxxxxxxxxxxxx
Hello Friends,
I am designing a carrier pcb that provides interconnect between a CPU
module and
a video processing card.
The video card supports 4x PCIe, but the CPU module has only 2 PCIe lanes
available.
Since PCIe pairs are specified to have 100ohm differential impedance, 50
ohm
resistors to ground ought to
work on the unused TX pairs. Do I also need a .1u cap in series with the
resistors for the RX pairs?
Thanks,
Jim
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