Hi Andy, You are correct in assuming that the edge speed was a bit fast, I read the= data from the wrong ibis file! Apologies to all those who were choking over their coffee= over this one... Here is the right info extract: [Ramp] |Variable typ min max |=0D dV/dt_r 1.732/0.683n 1.922/0.882n 1.995/0.546n =0D dV/dt_f 2.781/1.886n 2.992/2.402n 3.117/1.339n Found I do have LineSim buried in a forgotten server so i'll post the most= effective termination results when I have run the simulation. Cheers, James=0D -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Andrew Ingraham Sent: 03 March 2005 16:20 To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Long T reflection problems *** WARNING *** This mail has originated outside your organization, either from an external partner or the Global Internet.=0D Keep this in mind if you answer this message.=0D I'm noticing that the signals are really "slow" (change infrequently), but that you expect them to have rather fast, sub-ns edges. Also that you expect very long lengths when the logic analyzer is attached. I don't have much experience with logic analyzers, but I would have thought that any modern one has some sort of isolation, probably in the form of buffer amps, in the test head that attaches to your board. Expecting any system to work with an extra meter or so of T-line attached, is NOT normal, and I doubt that a logic analyzer today would do that sort of thing. Logic analyzer vendors know about the SI problems that would be introduced by attaching a one or two meter line to a board trace, so they probably design them to present no more than a few centimeters at most of additional= length, followed by a buffer, before the cable back to their main unit. That being said, make sure that your model does that. It sounds like you could isolate your 150mm "stub" with a big resistor, and be done with it. With 500 ns signals, unless the logic analyzer needs to capture the signals in a lot less time than that, let it eat a few dozen nanoseconds by using big (>>50 ohm) resistors between the "T" and your= stub. With only 1.5cm between devices, getting two sets of series terminating resistors (one at each driver) wouldn't make sense. Or maybe you can live with your 150mm unterminated stubs and accept the reflections. If you've really got 500ns for signals to settle, crappy waveforms for the first dozen - even hundred - nanoseconds are OK as long= as they don't overshoot severely, or radiate. 5V signals with 0.3ns edges are really screamin'. Maybe they aren't quite that fast. Regards, Andy ------------------------------------------------------------------ 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: =0D //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 =0D ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** ------------------------------------------------------------------ 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