Then there are those pesky diodes on PCI inputs. dav0 David Lieby, SI Engineering Acuson Corporation, a Siemens Company Scott McMorrow wrote: > > Bob Perlman wrote: > > Hi - > > Yes, your bus is terminated, but not with resistors. The PCI spec > puts limits on driver V-I curves, which in turn puts bounds on the > driver output impedance. The bus is series-terminated for all > intents and purposes. > > What Bob and Lee say about the PCI bus is misleading. > > The PCI bus is generally not a series terminated bus. The bus was > designed to operate on reflected waves without termination and as a > result, the driver output impedance is quite low. PCI busses are > designed to have large amounts of overshoot, undershoot and ringing. > > The bus can be de-Q'd using series resistors as attenuation elements, > however, this can only be done with some serious care and analysis. > > best regards, > > scott > > -- > Scott McMorrow > Teraspeed Consulting Group LLC > 2926 SE Yamhill St. > Portland, OR 97214 > (503) 239-5536 > http://www.teraspeed.com > > > > >There's a difference between using multi-drop, series-terminated > >buses for transmitting synchronous data (usually OK) and using them > >to distribute clocks (usually a nightmare). > > > >Bob Perlman > > > >On Tue, 29 Oct 2002 10:27:58 -0600, Chan, Michael (Eng Hou) wrote: > > > > > >>I don't believe that statement is true. I have PCI bus that has 18 = > >>loadings on it and it is never terminated ( 33MHz ). > >> > >>-----Original Message----- > >>From: Ritchey Lee [mailto:leeritchey@xxxxxxxxxxxxx] > >>Sent: Tuesday, October 29, 2002 10:18 AM > >>To: sandord@xxxxxxxxxxxxx > >>Cc: si-list@xxxxxxxxxxxxx > >>Subject: [SI-LIST] Re: Why we need to use "Series resistor" at > >>Transmitter? > >> > >> > >>The PCI bus, whick all PCs contain, is series terminated. How many > >> > >> > >= > > > > > >>million of > >>those are there? Just have to be careful when you clock data off > >> > >> > >the = > > > > > >>bus. > >> > >>Lee > >> > >>Sandor Daranyi wrote: > >> > >> > >> > >>>>Jim, > >>>>=3D20 > >>>>In regard to your comment: "Series termination > >>>>shoulkd NEVER be used wher the path is going to more > >>>>than one input i.e bus configuration.". The ATA/IDE > >>>>interface used in PCs is series terminated at the > >>>>source and is bussed to two loads on data and > >>>>strobe lines. The number of working systems in the > >>>>field is in the millions (every PC that has 2 > >>>>drives). The value of the series termination is a > >>>>great consideration (in ATA it is 22-50ohms). > >>>>=3D20 > >>>>So series termination in busses can work. Though, I > >>>>recommend a thorough understanding of the system > >>>>before employing this technique. > >>>>=3D20 > >>>>=3D20 > >>>>Charles Hill, consultant > >>>> > >>>> > >>>I concur. In theory, I agree that it's not "nice", but I've seen > >>> > >>> > >= > > > > > >>series te=3D > >> > >> > >>>rminations (with no parallel termination at the far end) used = > >>> > >>> > >>successfull=3D > >> > >> > >>>y in designs where there were multiple inputs on a trace. "Never" > >>> > >>> > >= > > > > > >>sounds=3D > >> > >> > >>>neat but as with most good rules, there are exceptions. > >>> > >>>I also agree with the caveats. In the examples I remember, the > >>> > >>> > >system = > > > > > >>was =3D > >> > >> > >>>running at a low clock frequency and all the inputs (not more than > >>> > >>> > >3 = > > > > > >>in t=3D > >> > >> > >>>hat case) were close to each other at the end of a long trace. It > >>> > >>> > >was = > > > > > >>of=3D > >> > >> > >>>a daisy-chain topology, i.e. there were no branches on the trace, > >>> > >>> > >to = > > > > > >>min=3D > >> > >> > >>>imize the impedance discontinuities and reflections. The inputs > >>> > >>> > >had = > > > > > >>high=3D > >> > >> > >>>impedance. Of course, one gotta think twice, even thrice, before > >>> > >>> > >= > > > > > >>doing =3D > >> > >> > >>>this on a clock signal. > >>> > >>>Sandor > >>> > >>>--- > >>>Sandor Daranyi > >>>Snr Design Engineer > >>>Aristocrat Technologies Australia > >>> > >>>------------------------------------------------------------------ > >>>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 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 > >>> > >>> > >> > >> > >>-- Binary/unsupported file stripped by Ecartis -- > >>-- Type: text/x-vcard > >>-- File: vcard.vcf > >>-- Desc: Card for leeritchey@xxxxxxxxxxxxx > >> > >> > >>------------------------------------------------------------------ > >>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 archives are viewable at: =20 > >> //www.freelists.org/archives/si-list > >>or at our remote archives: > >> http://groups.yahoo.com/group/si-list/messages=20 > >>Old (prior to June 6, 2001) list archives are viewable at: > >> http://www.qsl.net/wb6tpu > >>=20 > >> > >>------------------------------------------------------------------ > >>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 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 > > 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 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 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 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