Monday, July 26, 2010

Help!!! - DDR3 ODT (On Die Termination)???

Gosh, figuring this stuff out is difficult. Anyone know how this actually works? Why is Rtt Nom variable? When is it in use? If Dynamic ODT is on then Rtt Nom is really only in use when nothing is going across the wires. RTT Wr is used during a write, and Rtt is disabled during a read. So what is Rtt Nom really used for? It can't be for when Dynamic ODT is off, because that still wouldn't explain why there are 2 settings. Is it needed to keep the wires clean and not bouncing when nothing is going across it? Perhaps, but then why are there 6 possible values? What am I missing????

I can't continue until I completely understand this stuff. Perhaps I need to take some analog classes, or read some analog for dummies books, and then this would become clear... Although I doubt it.

Saddened by my lack of understanding here.

It makes me so happy to learn something new, and that happened in spades tonight! Well at least I learned a bunch of analog stuff, and got a great explanation for Rtt Nom.

The key is that when there are multiple DDR3 chips hooked up, and you are only writing to one of them, then Rtt Wr could be used for the one you are writing to, but the other one which shares the same DQ/DQS/DM lines needs to be terminated with Rtt Nom which must be calibrated because it will affect the signal integrity of the data being written. This is the explanation. I can't claim complete understanding or comprehension since I've not got near enough analog knowledge or experience, but for my simplistic understanding, this suffices very well!

So much happier now :)

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