The following table defines routing rules for DDR4 signals.
| Parameter | Value |
|---|---|
| Impedance Rules | |
| Impedance for single-ended CAC 1 and data signals | 50Ω 2 ± 10% |
| Impedance for differential clock (CK) and data strobe (DQS) | 90Ω 2 ± 10% |
| Trace Length Rules (from Adaptive SoC to Furthest Device or Termination) | |
| Maximum PCB trace length for CAC signals | 11000 mils |
| Maximum PCB trace length for data/strobe signals | 5500 mil |
| Spacing Rules for CAC Signals | |
| Minimum spacing between CAC signals |
2H 3 , except: 1H under adaptive SoC 1.5H under DDR4 device |
| Minimum spacing between CAC signals and clock signals |
5H, except: 2H under adaptive SoC 2H under DDR4 device |
| Minimum spacing between CAC signals and data signals |
5H, except: 2H under adaptive SoC 2H under DDR4 device |
| Spacing Rules for Data and Data Strobe Signals | |
| Minimum spacing between data/strobe signals within the same byte |
2H, except: 1H under adaptive SoC 1.5H under DDR4 device |
| Minimum spacing between data/strobe signals to data/strobe signals in other bytes |
5H, except: 2H under adaptive SoC 2H under DDR4 device |
| Spacing Rules for Signals between Memory Interfaces | |
| Minimum spacing between signals in one memory interface to signals in another memory interface |
5H, except: 2H under adaptive SoC 2H under DDR4 device |
| Maximum Via Count per Signal Type | |
| CAC signals and clock signals | (2 × # of devices) + 2 |
| Data and strobe signals | 2 |
| Other Physical Design Requirements | |
| Do not route CAC/clock signals on more than two internal signal layers | |
| Do not route data/strobe signals on more than one internal signal layer | |
| Route data/strobe signals on internal layers as close to the memory devices as possible | |
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