SPRABI1D January   2018  – July 2022 66AK2E05 , 66AK2G12 , 66AK2H06 , 66AK2H12 , 66AK2H14 , 66AK2L06 , AM5K2E02 , AM5K2E04 , SM320C6678-HIREL , TMS320C6652 , TMS320C6654 , TMS320C6655 , TMS320C6657 , TMS320C6670 , TMS320C6671 , TMS320C6672 , TMS320C6674 , TMS320C6678

 

  1.   Trademarks
  2. 1 Introduction
  3. 2 Background
  4. 3 Migrating Designs From DDR2 to DDR3 (Features and Comparisons)
    1. 3.1 Topologies
      1. 3.1.1 Balanced Line Topology
        1. 3.1.1.1 Balanced Line Topology Issues
      2. 3.1.2 Fly-By Topology
        1. 3.1.2.1 Balanced Line Topology Issues
    2. 3.2 ECC (Error Correction)
    3. 3.3 DDR3 Features and Improvements
      1. 3.3.1 Read Leveling
      2. 3.3.2 Write Leveling
      3. 3.3.3 Pre-fetch
      4. 3.3.4 ZQ Calibration
      5. 3.3.5 Reset Pin Functionality
      6. 3.3.6 Additional DDR2 to DDR3 Differences
  5. 4 Prerequisites
    1. 4.1 High Speed Designs
    2. 4.2 JEDEC DDR3 Specification – Compatibility and Familiarity
    3. 4.3 Memory Types
    4. 4.4 Memory Speeds
    5. 4.5 Addressable Memory Space
    6. 4.6 DDR3 SDRAM/UDIMM Memories, Topologies, and Configurations
      1. 4.6.1 Topologies
      2. 4.6.2 Configurations
        1. 4.6.2.1 Memories – SDRAM Selection Criteria
    7. 4.7 DRAM Electrical Interface Requirements
      1. 4.7.1 Slew
      2. 4.7.2 Overshoot and Undershoot Specifications
        1. 4.7.2.1 Overshoot and Undershoot Example Calculations
      3. 4.7.3 Typical DDR3 AC and DC Characteristics
      4. 4.7.4 DDR3 Tolerances and Noise – Reference Signals
  6. 5 Package Selection
    1. 5.1 Summary
      1. 5.1.1 ×4 SDRAM
      2. 5.1.2 ×8 SDRAM
      3. 5.1.3 ×16 SDRAM
      4. 5.1.4 ×32 SDRAM
      5. 5.1.5 ×64 SDRAM
  7. 6 Physical Design and Implementation
    1. 6.1 Electrical Connections
      1. 6.1.1 Pin Connectivity and Unused Pins – SDRAM Examples
      2. 6.1.2 Pin Connectivity – ECC UDIMM and Non-ECC UDIMM Examples
    2. 6.2 Signal Terminations
      1. 6.2.1 External Terminations – When Using Read and Write Leveling
      2. 6.2.2 External Terminations – When Read and Write Leveling is Not Used
      3. 6.2.3 Internal Termination – On-Die Terminations
      4. 6.2.4 Active Terminations
      5. 6.2.5 Passive Terminations
      6. 6.2.6 Termination Component Selection
    3. 6.3 Mechanical Layout and Routing Considerations
      1. 6.3.1 Routing Considerations – SDRAMs
        1. 6.3.1.1  Mechanical Layout – SDRAMs
        2. 6.3.1.2  Stack Up – SDRAMs
        3. 6.3.1.3  Routing Rules – General Overview (SDRAMs)
        4. 6.3.1.4  Routing Rules – Address and Command Lines (SDRAMs)
        5. 6.3.1.5  Routing Rules – Control Lines (SDRAMs)
        6. 6.3.1.6  Routing Rules – Data Lines (SDRAMs)
        7. 6.3.1.7  Routing Rules – Clock Lines (SDRAMs)
        8. 6.3.1.8  Routing Rules – Power (SDRAMs)
        9. 6.3.1.9  Write Leveling Limit Impact on Routing – KeyStone I
        10. 6.3.1.10 Round-Trip Delay Impact on Routing – KeyStone I
        11. 6.3.1.11 Write Leveling Limit Impact on Routing – KeyStone II
        12. 6.3.1.12 Round-Trip Delay Impact on Routing – KeyStone II
      2. 6.3.2 Routing Considerations – UDIMMs
        1. 6.3.2.1 Mechanical Layout – UDIMMs
        2. 6.3.2.2 Stack Up – UDIMMs
        3. 6.3.2.3 Routing Rules – General Overview (UDIMMs)
        4. 6.3.2.4 Routing Rules – Address and Command Lines (UDIMMs)
        5. 6.3.2.5 Routing Rules – Control Lines (UDIMMs)
        6. 6.3.2.6 Routing Rules – Data Lines (UDIMMs)
        7. 6.3.2.7 Routing Rules – Clock Lines (UDIMMs)
        8. 6.3.2.8 Routing Rules – Power (UDIMMs)
        9. 6.3.2.9 Write-Leveling Limit Impact on Routing
    4. 6.4 Timing Considerations
    5. 6.5 Impedance Considerations
      1. 6.5.1 Routing Impedances – KeyStone I Devices
        1. 6.5.1.1 Data Group Signals
        2. 6.5.1.2 Fly-By Signals
      2. 6.5.2 Routing Impedances – KeyStone II Devices
        1. 6.5.2.1 Data Group Signals
        2. 6.5.2.2 Fly-By Signals
      3. 6.5.3 Comparison to JEDEC UDIMM Impedance Recommendations
    6. 6.6 Switching and Output Considerations
  8. 7 Simulation and Modeling
    1. 7.1 Simulation and Modeling
    2. 7.2 Tools
    3. 7.3 Models
    4. 7.4 TI Commitment
  9. 8 Power
    1. 8.1 DDR3 SDRAM Power Requirements
      1. 8.1.1 Vref Voltage Requirements
      2. 8.1.2 VTT Voltage Requirements
    2. 8.2 DSP DDR3 Power Requirements
    3. 8.3 DDR3 Power Estimation
    4. 8.4 DSP DDR3 Interface Power Estimation
    5. 8.5 Sequencing – DDR3 and DSP
  10. 9 Disclaimers
  11. 10References
  12. 11Revision History

6.3.1.11 Write Leveling Limit Impact on Routing – KeyStone II

The write-leveling process in the DDR3 interface imposes a limit on the maximum and minimum skew between the command delay and the data delay. If these limits are exceeded, the DDR3 interface may fail the write leveling process and data corruption may occur. These limits are sufficiently large that well-controlled topologies will not likely exceed the limits.

The command delay is defined as delay for the clock, command, control, and address group signals from the DSP to a given SDRAM. The data delay is the delay for the data group signals to that same SDRAM. The write-leveling result is effectively the difference, or skew, between these two delays.

The maximum write-leveling skew is the largest difference between the two delays in the topology to a single SDRAM. Likewise, the minimum write-leveling skew is the smallest difference between the two delays in the topology to a single SDRAM. The write-leveling logic has an upper limit which is the lower of 1.75 clock periods or 2500 ps. For instance, when operating at 1600MT/s, the clock is 800MHz which has a period of 1250ps. The maximum skew is 1.75 clock periods or 2187ps. At a propagation delay of 180ps per inch, this limits the write-leveling routing skew length to just over 12.1 inches.

The minimum write leveling skew occurs when the command delay is less than the data delay. The minimum write-leveling skew is -0.75 times the clock period. At 1600MT/s, this minimum skew is 937ps or about 5.2 inches. The DDR3 PHY implemented on KeyStone II can operate within these limits without the need to invert the clock to the DDR3 SDRAMs.