Hi all, In our simulations, PCI66 with 3 slots is OK, with 4 slots, then the trace layout has to be well controlled, and trace on card has to follow some high speed layout rules like not-crossing-plane-slits. For more than 5 slots, the I/O buffer design is very difficult and has to trade off between timing and bounce across PVT corners, and would be very sensitive to topology. Best Regards Weber Chuang Signal & Timing Integrity Engineer, VIA Technologies, Inc. Taipei, Taiwan, ROC TEL : 886-2-22185452 ext : 6522 mailto:weber@xxxxxxxxxx http://www.via.com.tw Very Innovative Architecture -----Original Message----- From: Ingraham, Andrew [mailto:Andrew.Ingraham@xxxxxxxxxx] Sent: Thursday, August 30, 2001 9:36 PM To: SI Subject: [SI-LIST] Re: PCI at 66 Mhz The PCI Specification does not define a limit on number of loads, for either 33MHz or 66MHz. The system (motherboard) designer must make a compromise, between number of loads, how they are routed, and the PCI clock speed at which he wishes to run the bus. From a practical point of view, I doubt anyone could get PCI to work at 66 MHz with eight loads. The PCI Spec does hint that it may be impossible to have more than one PCI card per 66 MHz PCI bus, but I am aware that people have made 66 MHz PCI work with two card slots. How well they work, I can't say. "It ain't easy." PCI-X at 66 MHz is easier to do than PCI at 66 MHz. > Take your load capacitance, spec sheet and then it is simple. I doubt it's that simple. The bus is not a very good approximation to a lumped capacitive load. The actual topography (whether devices are on the motherboard or on plug-in cards, which means stubs, etc.) makes a difference too. PCI buses tend to have some amount of ringing, and the ringback often sets the maximum Tprop. Regards, Andy ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field 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 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