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DDR3 CKE recommendation

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fletch's picture
Bryan Fletcher
Junior(0)
DDR3 CKE recommendation

Xilinx has recently changed their recommendation for DDR3 CKE.  ZedBoard Rev C implements a 4.7K-ohm pulldown to GND.  The new recommendation is a 40-ohm pull-up to Vtt.
The Micron spec only requires CKE to be low 10ns before RESET#, unlike DDR2 where the term was longer. Since the Zynq controller drives CKE low, that 10ns requirement is met.  The termination to VTT could be important for self-refresh users, as CKE will toggle more often than just startup. The 4.7K pulldown may lead to poor SI on this potentially high-frequency signal.
Bryan

TimDuffy's picture
Timothy Duffy
Junior(0)
Bryan,

fletch,

Does this apply for both the PS *and* any PL MIG based DDR3 interface(s)? Or just the PS connection(s)?

fletch's picture
Bryan Fletcher
Junior(0)
This applies to all DDR3. 

This applies to all DDR3.  MIG is being updated to reflect this even for other 7-series.  If you look at a Micron DIMM, this is how it is done on the DDR3 DIMMs.
Bryan