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I have a 4-layer board with the micro and sdram on opposite sides, the ram signals are short, but I still want to terminate them (I can test the board later and determine if I really need termination), the problem now is that I can't use series termination because traces are running under the micro and ram:

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So what other choices do I have ? I've been reading an app note and it mentions parallel termination at the destination, which would be perfect for my situation, but it says signals should be pulled up, and another one says they should be pulled down, so which way is it ? does it matter ? and how do I determine this resistor ? and which lines need termination ? clocks and data/address ? what about control signals ?

mux
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We need to know what RAM generation you are using? DDR 4/3/2/1?

For efficiency you should determine if you need termination before you even route the board. See this question: What types of signals should be considered to have a 50 Ω trace impedance?

PS: There is a lot of free and good examples on how DDRx memory systems can be routed on the JEDEC website.

Community
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Rolf Ostergaard
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  • the ram is SDR actually, and the I/O rise/fall time is 2.5ns for the highest frequency, I'm almost sure I don't need them, just wanted to be on the safe side. – mux Jun 06 '14 at 12:14