Hello Bernd-- A few suggestions for you: 1. You are correct, putting TX and RX on different layers would alleviate near-end crosstalk, but then you have an issue with the far-end crosstalk, which will in most cases be a larger problem, especially on the outer layers. This paper may help: http://www.xilinx.com/publications/xcellonline/xcell_58/xc_pdf/p074-076_ 58-mentor.pdf There is also a PCI-Express Design Kit with lots of helpful tips on Mentor's SupportNet if you are a customer. 2. The are many straight connectors which support multi-Gbs signals (if your boards are parallel). Any of the major connector websites should have details. Or if you do have to cable the signals, I would stay away from a flat ribbon cable, but something like the twinax of a SATA cable might work well and is relatively flat. --Pat Patrick Carrier Technical Marketing Engineer High Speed Design Mentor Graphics Corporation Patrick_Carrier@xxxxxxxxxx ph. (512) 425-3015 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of bernd schuster Sent: Saturday, January 09, 2010 4:49 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] PCIe routing Hi, I`ve a few questions about using PCIe (using an four layer FR4 board). 1) Is it a good recommendation to route for example the RX pairs on the bottom layer and the TX pairs on the top layer to reduce near-end crosstalk? 2) Do you know any board-to-board (e.g with flat cable) connectors (not for PCIe slots) which are recommend to use for PCIe signals? I`ve one motherboard and a board with all the outputs installed (which are not perpendicular to each other) 3) Are there any recommendation I have to know adding a PCIe switch? The first thing I recognized was the delay of 128ns - what about the PCIe clock signal? best regards Bernd ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu