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).
For DDR4 two DIMM per channel (2DPC) designs, Intel® recommends placing the two DIMM connectors for a channel on both the top and bottom sides of the board, for best performance.
Figure 106. Signal connections for DDR4 2DPC SODIMM configuration using SMT DIMM connector
(In the above figure, CLK, CTRL refers to the per-DIMM signals (mem_ck, mem_cke, mem_odt) and remain as point-to-point connections.)
The following table provides specific routing guidelines for two DIMMs per channel in SODIMM topologies for all supported signals in the interface.
Table 111. Specific DDR4 2DPC routing guidelines for SODIMM configurations
Signal Group |
Segment |
Routing Layer |
Max Length (mil) |
Target Zse (ohms) |
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 |
300 |
|
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 |
300 |
|
4 |
8 (2h) |
12, (3h) |
|
|
|
|
|
CTRL |
BO1 |
US |
50 |
5000 |
|
4 |
5, 17 |
5, 17 |
|
|
|
|
|
BO2 |
SL |
1000 |
|
4 |
5, 17 |
5, 17 |
|
|
|
|
|
M |
SL |
|
45 |
4.5 |
8 (2h) |
12 (3h) |
|
|
|
|
|
BI |
US |
300 |
|
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 |
300 |
|
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 |
300 |
|
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 107. Reset scheme for 2DPC DIMM topologies
The target impedance for 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.