My first response is - huh? I guess at any time, we all risk being misunderstood. Students seeking answers from all the great gurus resident on this list, see below for the well written response. Eric, can we save this in the archive under "attention all students" and then pull it out anytime one posts seeking answers for his homework/project? - Bill, always a student but long out of school. Eric Bogatin <eric@xxxxxxxxxxxxxxx> wrote: st1\:*{behavior:url(#default#ieooui) } Bill- You are asking the SI list to give you some specific design rules to follow to help you meet your design spec. I think the advice you are getting is basically that the precise design rule of what line width, what spacing, what dielectric thickness, what copper thickness to use, to achieve a particular target single ended or differential impedance, depends on your application and the tradeoffs you want between total board thickness, manufacturing design rules, interconnect density, routing constraints, design margin and cost. When you ask a general question, the information you get from this email group is about the process to use to find your answer, not the specific answers. What you are hearing from this group is that you first need to understand the principles behind the question you are asking, so you know if it's even the right question, and what to do with the answer when you get it. Next, you need the right tools to translate general design guidelines into specific design rules. If you want a narrow design margin for a target impedance, and not over design your products, you need an accurate analysis tool, like a 2D field solver. If all you need is 10-20% accuracy, feel free to use the tables and charts you see in various books. You can use a free online calculator that is accurate to between 3-10%, or rent a 2D field solver, for about $20 an hour from the Polar Instruments web site that is accurate to 1%. When you see folks on this list saying, "do your homework", I think we are referring to understand the essential principles- check some of the books or classes or freely available feature articles already posted on various web sites, learn to use the tools already available to you, and learn to apply the principles and tools to your applications. If you don?t want to do your homework so you can solve your own problems, which is perfectly ok, there are a number of SI-list regulars who would be delighted to consult for you. --eric ******************************************************* Eric Bogatin Signal Integrity Evangelist Bogatin Enterprises Setting the Standard for Signal Integrity Training 26235 W 110th Terr Olathe, KS 66061 e: eric@xxxxxxxxxxxxxxx v: 913-393-1305 cell: 913-424-4333 f: 913-393-0929 www.BeTheSignal.com *********************************************** -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Bill Owsley Sent: Wednesday, May 30, 2007 10:14 PM To: Sam.Charles@xxxxxxxx; jeff.loyer@xxxxxxxxx Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx; weirsi@xxxxxxxxxx Subject: [SI-LIST] Re: IEEE1394/Ethernet Routing Guidelines I went below to check what Mr.Voorhies asked for; "...have had a very difficult time finding exact numbers for trace spacing/individual trace impedence and so on." And now I don't find in any of the suggestions (or in Mr.Voorhies note) anything about copper weight, dielectric constant at what frequency, trace width, distance above or between reference planes, length matching, number of vias across how many layers, crosstalk coupling factor and it's effect on even/odd mode impedance, pre-emphasis to compensate for longer lengths at higher frequencies, various "cute tricks" to emulate differential signals (one I really like, nearly eliminates most of the above), differential drivers or complementary drivers or current steering drivers, differential to common mode conversion factor, terminations, decoupling, and so on. All the books/sources referenced have all the conflicting information that Mr. Voorhies has already discovered. For us, immersed in the culture (or lack of it on my part) the references are like preaching to the choir, we nod our collective heads in agreement that those are indeed good sources and Mr. Voorhies says to himself, Hey I can catch lightning in a jar, but I still don't WTF they just said, thus the reason for his request. Everyday we work with digit heads, okay, digital guys, who connect to the dots and then look to the SI and EMC guys to make the board work. ps. we work well together cuz the only dots I connect are in my granddaughters coloring book. So given the dearth of details here's one answer (of many) he can use; 50 ohm surface traces (no vias), spaced 5 times the distance to the reference plane, no breaks in the plane below the traces, matched lengths to within 1 mil. (my layout guys can do that in about 30 seconds all day, another "cute trick"), and all added parts are absolute mirrow symmetric (the parts might need vias). --------------------------------- Finding fabulous fares is fun. Let Yahoo! FareChase search your favorite travel sites to find flight and hotel bargains. ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net 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