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DDR-ram interface (xapp200)

Hi,

I'm working on a University project that requires ddr-ram interfaced to a Vertex-EM device. I am basing my design off xapp200 from xilinx. The design uses DLLs to deskew the system clock and ddr-ram clock. The signal fed back to the DLLs (sys_clk_fb) is apparently the ddr clk. What I don't understand is where I take this signal from. Should I have tracks on my PCB comming back from the ddr-ram chips to inputs on the fpga? Or can the feedback signal come from inside the fpga?

I am a little lost as to how the DLLs manage to sychronise the two clocks. Any help would be appreciated.

Thanks.

Michael.

Reply to
Michael Chan
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Thanks for the help Bob. I think I know what I have to do.

Cheers,

Michael.

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Reply to
Michael Chan

I highly recommend the section on Eliminating Clock Skew in XAPP462: Using Digital Clock Managers (DCMs) in Spartan-3 FPGAs. The section begins on the bottom of page 25.

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Although the application note is written for Spartan-3 FPGAs, the DCM is functionally very similar to Virtex-II and Virtex-II Pro. The differences are also described in the application note.

--------------------------------- Steven K. Knapp Spartan-3/II/IIE FPGAs

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--------------------------------- Spartan-3: Make it Your ASIC

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Reply to
Steven K. Knapp

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