hello Allan, Being a I/O designer, I don't know much about board design, but I feel you are correct. Also it seems to defeat one more of it's purpose i.e. on-chip I/O power dissipation. Series resistor minimize on-chip power dissipation, since some of the i/o power is moved off chip and dissipated in the stub resistor, but SSTL series resistor on-chip defeats this too. better comments and corrections are awaited. Thanks Rajat > > Hi all: > Let's take the example of a motherboard with DRAMs on plug-in DIMM > cards, SSTL signaling levels, the bus on the motherboard parallel > terminated at both ends. It is my understanding that the series > resistors used in SSTL applications are there to effectively isolate the > stubs (caused by the DIMM traces) from signals traveling along the main > bus on the motherboard. Assuming that the series resistors are > physically on the DIMM, this would imply that they should be placed as > close as possible to the edge fingers, minimizing the stubs seen by the > main bus. Also, when a DIMM is driving, the series resistors reduce the > signal swing on the parallel-terminated main bus, resulting in faster > switching. First question, is my understanding pretty much correct, or > am I off-base here? > > Recently, I have seen application notes for devices where the SSTL > series resistor appears to be integrated "on-chip". While I can see that > this will help with reducing the output swing, it seems to defeat the > stub-isolating purpose of the series resistor. Any stubs would now be on > the bus-side of the resistor rather than being hidden from the bus. > Second question, am I missing something here, or does integrating the > SSTL series resistor on-chip defeat one of it's main purposes? > > I appreciate any insight you have. Thanks a lot! > Regards, Allan > ------------------------------------------------------------------ > 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 > > > ____________________________________________ RAJAT CHAUHAN STMicroelectronics NOIDA ------------------------------------------------------------------ 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