DDR5 Terminations Configuration
The DDR5 Specification defines RCD and DRAM registers for controlling termination levels for specific signals under certain conditions. These settings can be controlled here. You select the desired termination level and then press Change Settings to program the configuration into the subject module and device.
For compatibility with test equipment, including Oscilloscopes and BER Testers, it is important to choose settings that most-closely presents an effective resistance of 50 Ohms on the signal. So, for example, if only one Rank is in use, the 48 Ohm setting would be used. However, if a 15 Ohm resistor is placed in series between the DRAM and the connector, you would need to select the 34 Ohm setting to accomplish an effective resistance of 49 Ohms.
If two Ranks are in use, then the effective resistance is calculated as the series resistor in combination with two parallel resistors.
These selections must be chosen to accomplish the best signal integrity to/from the target rank, while also providing an effective resistance that is as close to 50 Ohms as possible.
Target rank refers the the rank being tested in a multi-rank module. Non-target rank refers to the other ranks not being tested.
Groups A and B refer to the order for particular DRAMs beginning at the one closest to the center RCD and extending to the outer-most DRAMS. The outer-most DRAMs are in Group B, and all the other DRAMs are in Group A.
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RTT_PARK |
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Off, 240Ohm, 120Ohm, 80Ohm, 60Ohm, 48Ohm, 40Ohm, 34Ohm |
Selection for RTT on the DQ signals. Separate selections for target and non-target ranks. |
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DQS_RTT_PARK |
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Off, 240Ohm, 120Ohm, 80Ohm, 60Ohm, 48Ohm, 40Ohm, 34Ohm |
Selection for RTT on the DQS signals. Separate selections for target and non-target ranks. |
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RTT_NOM_RD |
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Off, 240Ohm, 120Ohm, 80Ohm, 60Ohm, 48Ohm, 40Ohm, 34Ohm |
Selection for RTT on DQ signal during read operation used on the target rank when transmitting. |
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CA ODT |
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Off, 480Ohm, 240Ohm, 80Ohm, 60Ohm, 40Ohm |
Selection for on-die termination on the CA signal into DRAMs. Separate selections for DRAMs in group A and group B. |
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CK ODT |
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Off, 480Ohm, 240Ohm, 80Ohm, 60Ohm, 40Ohm |
Selection for on-die termination on the CK signal into DRAMs. Separate selections for DRAMs in group A and group B. |
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Change Settings Button |
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Programs the current selections into the devices on the connected module. |
See Also