On Tuesday 16 October 2007 13:57:54 Ing. Daniel Rozsnyó wrote: > Sebastien Bourdeauducq wrote: > > Hi, > > > > I've had a look at the board schematics from Transversal Technology, and > > I wonder why termination resistors that connect the DDRAM signal lines to > > a 1.25V (Vtt) supply are not present. From what can be read in various > > sources, DDRAM uses SSTL-2 signaling which requires that resistor (see > > http://download.micron.com/pdf/presentations/dram/plat7justin.pdf p.8 for > > instance). > > The presentation is about multiple DDR DIMM's, not single chips.
That's the same, DIMM DDR memory modules contain only the chips plus the series resistor in the 20-30 ohm range, and a serial EEPROM to store information about the chips used. See an example schematics at www.elixir-memory.com/products/file/Elixir_ DDR_512MB_B%20Die_TSOP_SODIMM_R1.0%20-%20160806.pdf p.5 ; and a quick visual inspection of a memory module from a PC shows the same. > > Is that because the PCB traces are short enough that you can get rid of > > that resistor and still get good signal integrity ? > > I think this is because point-to-point links. What do you call a "point to point" link ? See the SSTL-2 spec at http://download.micron.com/pdf/misc/sstl_2spec.pdf. There is nothing about that "point to point" thing. > And the chips already > contain some termination circuitry. Are you sure about this point ? I've always read the opposite. _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
