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

2.3.2 Probe the MDI Signals

In the default configuration, Auto-negotiation and Auto-MDIX can be enabled. A link pulse needs to be visible on the channel transmit (TD_P, TD_M) and can occasionally toggle to the receive pair (RD_P, RD_M). If set to MDI, this pulse is only available on the transmit pair while if set in MDI-X, this will only be available on the receive pair. A short Ethernet cable terminated with 100 Ohm differential needs to be used for measuring the MDI signals. A terminated cable is shown in Figure 2-7. A connection diagram for making measurements with the terminated cable is shown in Figure 2-8.

100Ω Terminated Cable Figure 2-7 100Ω Terminated Cable
100Ω Terminated Cable Connection Diagram Figure 2-8 100Ω Terminated Cable Connection Diagram

Auto-negotiation link pulses are nominally 100ns wide. Pulses are spaced by 62µs or 125µs and are transmitted in bursts. The bursts are nominally 2ms in duration and occur every 16ms. Figure 2-9 shows a link pulse.

Link Pulse Example Figure 2-9 Link Pulse Example