SNLA431 January   2024 DP83TC812R-Q1 , DP83TC812S-Q1

 

  1.   1
  2.   Trademarks
  3. 1Preface
  4.   Notational Conventions
  5. 2Related Documentation
  6. 3Support Resources
  7. 4Troubleshooting the PHY Application
    1. 4.1  Schematic and Layout Checklist
    2. 4.2  Verify Successful Power-up of PHY
    3. 4.3  Peripheral Pin Checks
      1. 4.3.1 Probe the RESET_N pin
      2. 4.3.2 Probe the INH pin
      3. 4.3.3 Probe the CLKOUT pin
      4. 4.3.4 Probe the Serial Management Interface (MDC, MDIO) Pins
    4. 4.4  Register Dump Comparison
    5. 4.5  Verifying Strap Configurations
    6. 4.6  Check the MDI Signal
    7. 4.7  Link Up Failed Common Issues
    8. 4.8  Signal Quality Check
    9. 4.9  Power Up Timing
    10. 4.10 Loopback Testing
    11. 4.11 Debugging the MAC Interface
    12. 4.12 Verify Open Alliance PMA Compliance
    13. 4.13 Tools and References
      1. 4.13.1 DP83TC812 Register Access
      2. 4.13.2 DP83TC812 USB2MDIO Scripts
      3. 4.13.3 Extended Register Access
      4. 4.13.4 Software and Driver Debug on Linux
        1. 4.13.4.1 Commonly Seen Linux Terminal Outputs
  8. 5Conclusion

4.8 Signal Quality Check

Once link up is confirmed by reading register 0x1 = 0x0065, you can check the quality of the link by utilizing the Signal Quality Indicator (SQI) feature of the DP83TC812. Poor link quality caused by layout or cable imperfections has the potential to lead to packet errors in the bit stream or link drops.

SQI is a method of quantifying the signal quality by measuring the signal to noise ratio, specified by Open Alliance. The value can range from 0 to 7 with 7 corresponding to the best link quality. Register 0x871 bits[3:1] can be read to identify the 3 bit SQI value. Read this register and verify the value is greater than 4 to maintain excellent link quality. Values less than 4 can point to an imperfection in schematic/layout, cable, or being in a noisy environment. Please verify that your design is meeting the recommendations given in the DP83TC812 Schematic and Layout Checklist.

Additionally, verify the script given in SNLA389 has been written to the PHY. This script must be written to maintain the best signal quality.

Table 4-5 DP83TC812 SQI Mapping

Reg 0x871[3:1]

Open Alliance SQI Level

Link Quality

0x0

0 (Worst)

Poor or No Link

0x1

1

0x2

2

0x3

3

0x4

4

Good or Excellent Link

0x5

5

0x6

6

0x7

7 (Best)