Stephen, I am using a typical DDR PTP topology, with a series termination and a parallel termination to VTT, with two IOs, one for an ASIC and one for the memory. Since I am simulating AND measuring at the pin, I do not see how the package parasitics play here. And, yes, I am measuring at exaclty the same threshold voltage. The slew rate is different, since I have two different IOs. Thanks, /dan --- Stephen Zinck <signalintegrity@xxxxxxxxxxx> wrote: > Hi Dan, > > Maybe you could give the list a little more detail > as far as the topology, > etc for the circuit in question. > > But off the cuff, my guess would be loading > differences between > bi-directional drivers. You may have two loads at > the memory and one at the > controller. Package models may be sufficiently > different to cause some the > delay differences you are seeing as well. Finally, > you may have a single > parallel term down one end (near the SDRAM) or two > series terms with > different values that could cause edge-rate > differences, which would > manifest itself as different delay characteristics > depending on drive > direction. By the way, how are you measuring delay > (i.e. to the vdd/2 > threshold point, etc.?)? > > Regards, > Steve > > Stephen P. Zinck > Interconnect Engineering > 25 Bennett Lot Road > South Berwick, ME 03908 > Phone - (207) 384-8280 > Fax - (207) 384-5388 > Email - szinck@xxxxxxxxxxxxxxxxxxxxxxxxxxx > Web - www.interconnectengineering.com > > > ----- Original Message ----- > From: "Dan Bostan" <dbostan@xxxxxxxxx> > To: "'Si-List'" <si-list@xxxxxxxxxxxxx> > Sent: Monday, January 31, 2005 2:20 PM > Subject: [SI-LIST] Propagation delay question > > > > Fellow SI members, > > Could anyone explain to me why the propagation > delay, > > simulated and measured at the pin, on a > bidirectional > > DQS line, for a DDR memory, is different for a > write > > cycle vs. a read cycle? > > Obviously, the transmission line is identical, > only > > the drivers are different. > > /dan > > > > > > > > > > > > __________________________________ > > Do you Yahoo!? > > Take Yahoo! Mail with you! Get it on your mobile > phone. > > http://mobile.yahoo.com/maildemo > > > ------------------------------------------------------------------ > > 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 FAQ wiki page is located at: > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > List technical documents are available at: > > http://www.si-list.org > > > > 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 > > > > > > __________________________________ Do you Yahoo!? Yahoo! Mail - 250MB free storage. Do more. Manage less. http://info.mail.yahoo.com/mail_250 ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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