SDAA081 September   2025 DP83825I

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Troubleshooting the Application
    1. 2.1 Schematic 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
      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
      4. 2.3.4 Compliance
    4. 2.4 RMII Health 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. 3Summary
  7. 4References

2.3.3 Check the Link Quality

After establishing a valid link, confirming the key status register values and visually verifying that the link LED is lit, the next data transfer debug step is to check the MAC Interface. There are several possible sources of link problems:

  1. Link partner transmit problem
  2. Cable length and quality
  3. 25MHz reference clock quality
  4. MDI signal quality

With the PHY powered and connected to a link partner, register 0x218 can be used to determine link quality. Read the register value to determine the Mean Square Error (MSE). With the MSE value, refer to Table 2-6 to determine link quality:

Table 2-6 Link Quality Ranges
Link QualityMSE
Excellent0x020A > MSE
Good0x033B > MSE > 0x020A
PoorMSE > 0x033B