External Memory Interface Handbook Volume 2: Design Guidelines

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ID 683385
Date 5/08/2017
Public
Document Table of Contents

9.13.1.1. ISI Effects

With multiple chip selects and possible slots loading the far end of the pin, there may be ISI effects on a signal causing the eye openings for DQ, DQS, and address and command signals to be smaller than for single-rank designs.

The following figure shows the eye shrinkage for DQ signal of a single rank system (top) and multiple chip select system (bottom). The ISI eye reductions reduce the timing window available for both the write path and the address and command path analysis. You must specify them as output delay constraints in the .sdc.

Extra loading from the additional ranks causes the slew rate of signals from the FPGA to be reduced. This reduction in slew rate affects some of the memory parameters including data, address, command and control setup and hold times (tDS, tDH, tIS, and tIH).

Figure 95. Eye Shrinkage for DQ Signal


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