SNLA423A March   2023  – June 2025 DP83826E , DP83826I

 

  1.   1
  2.   Trademarks
  3. 1DP83826 Application Overview
  4. 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 and CEXT
      4. 2.2.4 Probe the XI Clock
      5. 2.2.5 Probe the Strap Pins During Initialization
      6. 2.2.6 Probe the Serial Management Interface Signals (MDC, MDIO)
        1. 2.2.6.1 Read and Check Register Values
          1. 2.2.6.1.1 Extended Register Access
    3. 2.3 MDI Health Checks
      1. 2.3.1 Magnetics
      2. 2.3.2 Probe the MDI Signals
      3. 2.3.3 Link Quality Check
      4. 2.3.4 Compliance
    4. 2.4 MII Health Checks
      1. 2.4.1 MII Check
      2. 2.4.2 RMII 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
  5. 3Summary
  6. 4References
  7. 5Revision History

2.5.2 Transmitting and Receiving Packets With the MAC

If generating and checking packets with the MAC is possible, and the PHY has a working link partner with reverse loopback capability, verify the full data path as follows:

  1. Power and connect the PHY to the MAC and a working link partner.
  2. Enable reverse loopback on the link partner (for DP83826 link partner, write 0x16 to 0010).
  3. Transmit test packets from the MAC to the PHY.
  4. Verify the MAC receives the same test packets.

If the MAC receives the same test packets transmitted without issue, the full data path through MAC → PHY → MDI is valid. If this test does not pass, perform MII loopback to isolate the issue along the data path:

  1. Power and connect the PHY to the MAC.
  2. Enable MII loopback on the PHY (write Reg 0x0[14] = '1').
  3. Transmit test packets from the MAC to the PHY.
  4. Verify the MAC receives the same test packets.

If the MAC receives the same test packets, the data path through MAC → PHY is valid, and the issue has been isolated to the MDI data path. If this test does not pass, the issue can be on the MAC interface or the internal data path. To verify the MAC interface, refer to Debugging MAC Interface. To verify the internal data path, perform PRBS with analog loopback using the following script.