External Memory Interface Handbook Volume 2: Design Guidelines

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

2.4.2. Dynamic On-Die Termination (ODT) in DDR4

In DDR4, in addition to the Rtt_nom and Rtt_wr values, which are applied during read and write respectively, a third option called Rtt_park is available. When Rtt_park is enabled, a selected termination value is set in the DRAM when ODT is driven low.

Rtt_nom and Rtt_wr work the same as in DDR3, which is described in Dynamic ODT for DDR3.

Refer to the DDR4 JEDEC specification or your memory vendor data sheet for details about available termination values and functional description for dynamic ODT in DDR4 devices.

For DDR4 LRDIMM, if SPD byte 152 calls for different values of Rtt_Park to be used for package ranks 0 and 1 versus package ranks 2 and 3, set the value to the larger of the two impedance settings.

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