SNLA475 October   2024 DS250DF410 , DS250DF810 , DS280BR810 , DS280BR820 , DS280DF810 , DS280MB810 , DS560MB410

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Codesign: 25GbE 4-Channel Retimer or Redriver with Crosspoint
    1. 2.1 DS250DF410 Retimer Overview
    2. 2.2 DS560MB410 Redriver Overview
    3. 2.3 Pin Comparison Table
    4. 2.4 Codesign Schematic Example
    5. 2.5 Notable Codesign Elements
      1. 2.5.1 Calibration Clock
      2. 2.5.2 SMBus Address
      3. 2.5.3 SMBus Controller Mode
      4. 2.5.4 SMBus Pull-Up Resistors
      5. 2.5.5 Interrupt Output
      6. 2.5.6 Mux Select Inputs
  6. 3Codesign: 25GbE 8-Channel Retimer or Redriver with Crosspoint
    1. 3.1 DS250DF810 and DS280DF810 Retimers Overview
    2. 3.2 DS280BR810, DS280BR820, and DS280MB810 Redrivers Overview
    3. 3.3 Pin Comparison Table
    4. 3.4 Codesign Schematic Example
    5. 3.5 Notable Codesign Elements
      1. 3.5.1 AC Coupling
      2. 3.5.2 Calibration Clock
      3. 3.5.3 SMBus Address
      4. 3.5.4 SMBus Controller Mode
      5. 3.5.5 SMBus Pull-Up Resistors
      6. 3.5.6 Interrupt Output
      7. 3.5.7 Mux Select Inputs
  7. 4Summary
  8. 5References

3.5.4 SMBus Controller Mode

Pin E3 (EN_SMB) is connected such that SMBus Target mode is selected for both DS2x0DF810, DS280BR8x0, and DS280MB810 by default. In SMBus Target mode, a controller accesses and modifies the retimer's or redriver's register configuration through the SMBus interface. In SMBus Controller mode, the retimer or redriver attempts to self-configure by reading the device settings stored in an external EEPROM.

DS2x0DF810, DS280BR8x0, and DS280MB810 can be reconfigured in SMBus Controller mode within this codesign example. The following design modifications need to be made.

  1. Depopulate R3 to select SMBus Controller mode on the EN_SMB pin.
  2. Depopulate R4 and populate R10 with a 1kΩ resistor. This pulls the READ_EN_N pin low to initiate EEPROM load.
  3. Populate R17 with a 0Ω resistor to connect the ALL_DONE_N pin output. If multiple devices share a single EEPROM, then connect the ALL_DONE_N output of the first device to the READ_EN_N input of the next device to prevent multiple devices attempting to read the EEPROM at the same time.
  4. Populate R31 and R32 with 0Ω resistors to connect the EEPROM SMBus interface to the retimer or redriver SDA and SDC pins.
  5. Place an external EEPROM in dipsocket XU1. Modify resistor straps R25 – R30, R33 – R35 as necessary. Note that the EEPROM 8-bit address must be 0xA0 and capable of 400kHz operation at 2.5V or 3.3V supply.