Does anyone have much experience connecting a single DDR3 to a processor?
I've got a couple of questions:
I'm looking at the routing on an evaluation board, the DDR3 is on the top of the board, the VTT termination resistors are on the bottom of the board but outside the via field required for the DDR3 BGA. The routing between the DDR3 and processor is on internal layers, so the routing from the DDR3 vias to the VTT termination resistors essentially create 'stubs' on the bottom of the board. These 'stubs' seem to be matched length on the evaluation board. Would this be the best/most correct way to do this - even though all routing guidelines says to not create stubs.
There has been some bit swapping of some of the data lines. I've found a couple of references online to this being a via solution to improve routing, but no description on why it actually works. Is it simply that whatever data you write out to the memory will come back as it was written out, even though it was stored differently on the memory.
For example, write out: 01010101 but at the other end of the data lines (at the memory) its: 01101100 due to bit swapping, but that doesn't matter because when you read it back it actually comes back as it was written out?
Thanks,
G