External Memory Interface Handbook Volume 2: Design Guidelines

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

3.2.5.3. Reading From Memory

In Table 5–2, the recommended ODT setting for a dual‑DIMM configuration with both slots occupied is to turn on the ODT feature using a setting of 75-ohm on the slot that is not read from. As there is an option for an ODT setting of 150-ohm, this section explores the usage of the 150-ohm setting and compares the results to that of the recommended 75-ohm.

Read From Memory in Slot 1 Using an ODT Setting of 75‑ohms  on Slot 2

The following figure shows the double parallel termination scheme (Class II) using ODT on the memory with the memory-side series resistor when the FPGA is reading from the memory using a full drive strength setting on the memory. In this scenario, the FPGA is reading from the memory in slot 1 and the ODT feature of the memory at slot 2 is turned on.

Figure 43. Double Parallel Termination Scheme (Class II) Using External Resistor and Memory-Side Series Resistor and ODT Feature Turned On


Read From Memory in Slot 2 Using an ODT Setting of 75‑ohms  on Slot 1

In this scenario, the FPGA is reading from the memory in slot 2 and the ODT feature of the memory at slot 1 is turned on.

Figure 44. Double Parallel Termination Scheme (Class II) Using External Resistor and a Memory-Side Series Resistor and ODT Feature Turned On


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