SNLA443A December   2023  – August 2025 DP83869HM

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1DP83869 Application Overview
  5. 2Troubleshooting the Application
    1. 2.1 Schematic and Layout Checklist
    2. 2.2 Device Health Checks
      1. 2.2.1 Voltage Checks
      2. 2.2.2 Probe the RESET_N Signal
      3. 2.2.3 Probe RBIAS
      4. 2.2.4 Probe the XI Clock
      5. 2.2.5 Probe the Strap Pins During Initialization
        1. 2.2.5.1 Configuring Correct Operational Mode
      6. 2.2.6 Probe the Serial Management Interface (MDC, MDIO)
        1. 2.2.6.1 Read and Check Register Values
    3. 2.3 MDI Health Checks
      1. 2.3.1 Magnetics
      2. 2.3.2 Probe the MDI Signals
      3. 2.3.3 Check the Link Quality
        1. 2.3.3.1 Improving Short Cable Link Margin
        2. 2.3.3.2 Improving Inter-channel Link Margin
      4. 2.3.4 Compliance
    4. 2.4 MII Health Checks
      1. 2.4.1 MII Check
      2. 2.4.2 RGMII Check
      3. 2.4.3 SGMII Check
    5. 2.5 Loopback and PRBS
      1. 2.5.1 Loopback Modes
      2. 2.5.2 Transmitting and Receiving Packets with the MAC
      3. 2.5.3 Transmitting and Receiving Packets with BIST
  6. 3Operational Mode Clarification
    1. 3.1 Bridge Modes
    2. 3.2 Fiber Configuration
      1. 3.2.1 Fiber Registers
      2. 3.2.2 Media Converter LED Behavior
  7. 4Tools and References
    1. 4.1 Extended Register Access
      1. 4.1.1 Read (No Post Increment) Operation
      2. 4.1.2 Write (No Post Increment) Operation
    2. 4.2 Software and Driver Debug on Linux
      1. 4.2.1 Common Terminal Outputs
  8. 5Summary
  9. 6References
  10. 7Revision History

3.2.1 Fiber Registers

DP83869HM has several fiber related registers, this section is intended to summarize a few of their functionalities and show how to debug. Link status can always be checked in register 0x01, but register 0xC01 checks Fiber link.

Table 3-1 Register 0xC01 Behavior
ModeRegister 0xC01 behavior
RGMII to FiberBehaves the same as register 0x01. There is no added benefit of reading register 0xC01
Media Convertor Mode

Case 1: Copper link is down but Fiber link is up

Register 0x01 indicates link is down (copper side), but register 0xC01 shows link is up (fiber side). This is helpful for being able to debug which cable is at fault.

Case 2: Copper link is up but Fiber link is down

Register 0x01 indicates link is down. If register 0xC01 says link is down, register 0x01 is also down.

Case 2 in Table 3-1 does not give full confidence in which link is down. The Fiber Interrupt Status Register (0xC19) can be used to isolate where the fault is. In Case 2, 0xC19[9] (Fiber Far End Fault) and 0xC19[4] (Link Status Change) can flag. In Case 1, only 0xC19[4] can flag.