On Tuesday 16 October 2007 16:24:32 Ing. Daniel Rozsnyó wrote: > Sebastien Bourdeauducq wrote: > >> P2P for me is a `direct chip to chip trace without branching`, in this > >> case also for 1 driver and 1 receiver per line (not counting address > >> lines now - they are a mystery even after reading the above pdfs, that > >> the termination is same for load of 2 (data) and 16 (addr) when using 2 > >> modules with 8 chips..). > > > > Maybe that's because the chip's input impedance on the address lines is > > high compared to Rt ? > > It should be no higher than the impendance on data inputs.. (from > diagrams the sstl2 receiver uses an opamp/comparator).
If the input impedance of the chip (regardless the pin is for address or data) is, say, 10000 ohm, and Rt is 50 ohm, the number of chips connected in parallel won't make a big difference. If we have one chip, the resulting impedance will be (50x10000)/(50+10000)=49.75 ohm, and with 10 chips, the input impedance for the chips will be 1000 ohm, and the resulting impedance on the line will be (50x1000)/(50+1000)=47.61 ohm. That's just a theory - I don't know what the input impedance of DDRAM chips is. Why do you think the fact that address lines are unidirectional should make a difference ? Regards, Sebastien _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
