External Memory Interfaces Intel® Agilex™ FPGA IP User Guide

ID 683216
Date 10/04/2021
Public

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6.5.5.2. Two DIMMs per Channel (2DPC) for UDIMM, RDIMM, and LRDIMM DDR4 Topologies

The interface covers data bytes (DQ/DQS), address signals, command signals (BA, BG, RAS, CAS, WE, ACT, PAR), control signals (CKE, CS, ODT), and clocks (CLK).

The following figure illustrates the signal connection topology for a PTH type of connector for UDIMM, RDIMM, and LRDIMM topologies.

Figure 83. Signal connections for DDR4 2DPC DIMM configuration using PTH DIMM connector

The following figure illustrates the signal connection topology for an SMT type of connector for UDIMM, RDIMM, and LRDIMM topologies.

Figure 84. Signal connections for DDR4 2DPC DIMM configuration using SMT DIMM connector

The following table provides specific routing guidelines for two DIMMs per channel in UDIMM, RDIMM, LRDIMM, and SODIMM topologies for all supported signals in the interface.

Table 103.  Specific DDR4 2DPC routing guidelines for UDIMM, RDIMM, LRDIMM, and SODIMM configurations
Signal Group Segment Routing Layer Max Length (mil) Target Zse (ohm) Trace Width, W (mil) Trace Spacing, S1 (mil): Within Group Trace Spacing, S2 (mil): CMD/CTRL/CLK to DQ/DQS Trace Spacing, S3 (mil):DQ Nibble to Nibble Trace Spacing (mil), Within DIFF Pair Trace Spacing (mil), DQS pair to DQ Trace Spacing (mil), CLK pair to CMD/CTRL/CKE Channel to Channel Spacing (DQ to DQ between two channels)
Segment Total MB
CLK BO1 US 50 5000   4 5, 17 5, 17   4   17  
BO2 SL 1000   4 5, 17 5, 17   4   17  
M SL   45 4.5   12 (3h)   4   12 (3h)  
BI US 50   4   12 (3h)   4   12 (3h)  
CMD, ALERT BO1 US 50 5000   4 5, 17 5, 17          
BO2 SL 1000   4 5, 17 5, 17          
M SL   40 5.5 8 (2h) 12 (3h)          
BI US 100   4 8 (2h) 12 (3h)          
D2D SL PTH: 340 SMT: 400   5.5 8 (2h) 12 (3h)          
CTRL BO1 US 50 5000   4 5, 17 5, 17          
BO2 SL 100   4 5, 17 5, 17          
M SL   45 4.5 8 (2h) 12 (3h)          
BI US 100   4   12 (3h)          
DQ BO1 US 50 5000   3 5, 17   17       17
BO2 SL 1000   3 5, 17   17       17
M SL   40 5.5 8 (2h)   12 (3h)       16 (4h)
BI US 50   4 8 (2h)   12 (3h)       16 (4h)
D2D SL PTH: 500 SMT: 400   4 8 (2h)   12 (3h)       16 (4h)
DQS BO1 US 50 5000   3 5, 17     4 17    
BO2 SL 1000   3 5, 17     4 17    
M SL   40 5.5       4 12 (3h)    
BI US 50   4              
D2D SL PTH: 500 SMT: 400   4              
For an explanation of the guidelines represented in this table, refer to the bullet points immediately following .

The following figure shows the RESET signal scheme and routing guideline for two DIMMs per channel topologies.

Figure 85. Reset scheme for 2DPC DIMM topologies

The target impedance for the RESET signal is 50 ohms. The RESET signal shall have at least 3×h (where h stands for trace to nearest reference plane height or distance) spacing to other nearby signals on the same layer. The end-to-end RESET trace length is not limited but shall not exceed 5 inches.