Ivor, This is kind of related to the another question I raised about buffer driver strengths in general. How does one describe a buffer's drive strength? I believe the only answer is with it's source impedance. This can be derived from a transmission line by measuring the porch voltage of the signal as it is launched onto the t-line (since you know the porch voltage level, Vdd, and the impedance of the t-line, you can solve for the source impedance). So to answer your question : you're right, there is no reflection level requirement. But there is a VI curve requirement that source impedance can be derived from (Zs should be the slope of the curve). If you look at the VI curves in the spec it shows a shaded area where the drive strength (or source Z) can be in. You can then compare it to your measurements from your spice sim's. (Spice sim should include a long t-line of a known value. Measure the initial voltage launched onto the t-line (sometimes referred to as the porch voltage)and solve for Zsource. regards, Jim -----Original Message----- From: IVOR TING [mailto:ivor.ting@xxxxxxxxxxx] Sent: Wednesday, August 01, 2001 7:42 PM To: SI Subject: [SI-LIST] pci driver strength Hi, I am working on an ASIC that has a 3.3V PCI 2.1 complianace interface and I am doing hspice simulation on the output buffer. I understand PCI uses reflected wave switching, so a buffer must not be too strong. My question is, is there a requirement saying that if the output before reflection is higher than a certain voltage, the driver is too strong? I couldn't find it in the specification itself. Thanks. Ivor. -- ************************************************************** Ivor Ting Email: ivor.ting@xxxxxxxxxxx ASIC Development, Alcatel CID Phone: (604)-453-3208 Suite 400-4190 Still Creek Drive Fax : (604)-421-2644 Burnaby, B.C., Canada, V5C 6C6 Web : www.cid.alcatel.com ************************************************************** ------------------------------------------------------------------ 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