Oops, it has been called to my attention that .5ns clock skew is for PCIX. PCI 33 has allowable clock skew of 2 ns. This does not make a strong arguement for matching your card clock length to 2.5 inches, but what can I say... the spec is as the spec is. JR -----Original Message----- From: James_R_Jones@xxxxxxxx [mailto:James_R_Jones@xxxxxxxx] Sent: Monday, July 29, 2002 3:39 PM To: zanglinyuan@xxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: PCI daughter card signal trace length PCI is a common clock architecture, meaning that it is assumed that clocks arrive at all devices on the bus simultaneously. There is an allowable skew of .5 ns for PCI 33. The motherboard designer will assume that you have designed for a 2.5 inch clock as well. So he knows how long to route his clock traces to each slot. The data/address traces should be limited to 1.5 inches, as the motherboard of the system will have lengths for bus assuming that the card traces will be no longer than 1.5 inches. If you design your PCI card in such a fashion, your trace lengths are PCI compliant. Most reputable computer designers will design their motherboards to be PCI compliant as well. If you put a PCI compliant card in a PCI compliant motherboard, then there should not be any signal integrity issues. Also, many PCI cards are not impedance controlled. Therefore, it is advantageous to have short traces that appear lumped to the rest of the system. Hope this helps, JR -----Original Message----- From: zanglinyuan [mailto:zanglinyuan@xxxxxxxxxx] Sent: Monday, July 29, 2002 1:31 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] PCI daughter card signal trace length Hi. In PCI daughter card,PCI Specification says the 32-bit portion of PCI bus must be limited to a maximum trace length 1.5 inches,and the 64-bit extension signals must be within 2 inches. However the CLK signal must be 2.5inches. Who knows the exact reason for the length limitations,expecially for CLK signal? ------------------------------------------------------------------ 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 archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages 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 archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages 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 archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu