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

2.2.6.1 Read and Check Register Values

Read the registers and verify the default values shown in the data sheet. Note that the initial values of some registers can vary based on strap options. The expected register values for PHY operation and link in 10/100Mbps with auto-negotiation enabled are shown in Table 2-4.

Table 2-4 DP83825 Register Value References
Register AddressRegister ValueComments
10Mbps100Mbps
0x000031003100Auto-negotiation enabled
0x0001786D786DLink established
0x0004006101E110/100Mbps advertisement
0x00104917 or 09174715 or 0715Auto negotiation status

With the PHY linked in a given speed, use these values as a reference to identify any variance from the expected operation. Note that not all registers need to be the same.

Example: After powering and linking the PHY in 10Mbps, Reg 0x10 contains the value 0x0017(Bits 4, 2, 1, 0 are high). This confirms:

  • Auto-Negotiation is complete
  • Full-Duplex
  • 10Mbps Mode
  • Link established

Repeating this process for any values distinct from the expected values shown in Table 2-4 help diagnose the exact state of the PHY for any encountered issues.