Does KeyStone II support TwinDie DDR3?

j-breeze,

The terms twin-die and dual-rank are not equivalent.  Twin-die can be in same rank but recently commoditized twin-die devices are in separate ranks.

KeyStone I devices can support up to 2 ranks but they do not support address mirroring.  Therefore, this allows twin-die devices using 2 ranks.  They do not support dual-rank DIMMs or SO-DIMMs that require address mirroring support.

KeyStone II devices do not have any of these limitations.  They support up to 2 ranks and they can support address mirroring.  The 2 ranks can be in separate SDRAM packages or in twin-die packages.  Please note that there is also the Keystone II DDR3 Initialization Application Report (SPRABX7).

Tom

j-breeze,

I know of multiple customer designs but I cannot provide details.  We also implemented a layout for twin-die devices on a 66AK2E05 test board that is fully functional.  There are no special requirements for twin-die topologies.  You still need to follow the routing rules in the guidelines document.  You will discover that the additional fly-by nets for the second set of control nets will cause the fly-by routing to take more area and perhaps another layer.  I recommend that you reference the JEDEC Unbuffered DIMM Design Specification, JEDEC Standard No. 21C 4.20.19.  It provides lots of guidance for complex and dense SDRAM topologies.

Tom