What is the advantage and disadvantage of Fly by topology and T topology ??

[kabaleevisu]

Hi everyone,

i worked in DDR2 and DDR3 Routing but. i studied some document related to DDR. For DDR3 Fly by (Daise chain) Topology is the best.but in DDR2 Address groups are routed in T-topology.

Here i attached DDR2 image. T-topolgy used.why we should not route the address signal group in Daisy chain topology ?? for DDR2. what is the different.

 

[FvM]

DDR3 is designed to support flight time compensation (write levelling), DDR2 isn't. Consider that some simplified DDR3 controllers are lacking the feature, thus still need the DDR2 like trace length compensation and can't work with DDR3 modules.