[Open-graphics] DDR Vtt termination ?

["Ing. Daniel Rozsnyó"]

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.

> 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. And the chips already 
contain some termination circuitry. (but then what about the termination 
of the shared address lines?)

D.