Flip the conceptual machinery around; critical length is by definition the boundary between where termination doesn't matter and where it does. It has no direct relation to backmatching at the driver, which is a popular way of terminating lines longer than critical length. Below critical length, the time delay on the line is short enough compared to the risetime of the signal that the voltage delta between the ends is small enough to ignore, i.e. the signal is 'local'. It's a fuzzy boundary that depends on lots of things, but another way to look at it is that if the transmission line is a small fraction of a wavelength, the energy reflected from a mismatched load is so nearly in phase with the driving end (or 180 degrees out, depending on the sign of reflection) that the formula that transforms load impedance to what is seen at the driving end never strays very far from unity. Therefore the transmission line is very nearly transparent and can be ignored (all else being equal), even to the point of not requiring matching at either end. A resistor might still be required for pull up, pull down, or voltage divider purposes, but on a short enough line there is no need to tie the value to trace impedance. Orin Laney On Thu, 17 Sep 2009 12:27:07 +0530 "Sonu Kurian N.D" <sonukurian@xxxxxxxxxxxxxxx> writes: > Hi All, > > I am puzzled about why termination is not required if trace length > is > less than critical length. > I read like if a driver encounters a reflected signal when it is > rising(driving) , its able to absorb reflection.Is it so? > Or is the situation like ..the reflections will be there..but the > Setup > condition can be met..so we need not worry..?? > Can anyone please throw some light on this.. > > Many thanks, > Sonu > > > > ------------------------------------------------------------------ > 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 > > > ____________________________________________________________ Lose up to 20 lbs in one month with a new diet. Click here. http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTFoYbnjpxpyPGuHaWex3S8KUp383121B6bTJ5YEE1gA7TmiP2s1GY/ ------------------------------------------------------------------ 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