maximum distanse beetwin SFP-module and FPGA (RocketIO) ???

axalay ha scritto:

You have to look at the rise time (tR) and fall time of your signals. My rule of thumb is that if distance D > (2/3)c tR; than you need terminations.

There are tons of documents on the subject.

I am currently using on SFP module at a distance of 71 mm. I don't use external termination resistors, if that is what you mean.

Yep, the rise time is the indicator. IIRC the usual rule of thumb is 1/6 Tr, as you say tullio, there's plenty of stuff on the www. Cheers, Syms.

Assuming he is using the Xilinx FPGAs, the FPGA has internal terminations. He should not be adding external termination resistors on the Rx signals.

And the SFP module should also have its RX pins terminated (and AC coupled) in the module. The TX pins are also AC coupled in the module.

Ed McGettigan

-- Xilinx Inc.

Thank for all !!! You are help me very much!

:) are you serious or it is joke? (it about distanse 70 and 71 mm)

"Duane Clark =D0=BF=D0=B8=D1=81=D0=B0=D0=BB(=D0=B0): "

No, it is serious ;) My PCB layout program will easily tell me the exact length of the traces, so I just fired it up and found out what the length was. I could have given the length to 3 decimal places, if desired ;)