SNLA491 August   2025 DP83826AE , DP83826AI

 

  1.   1
  2.   Trademarks
  3. 1DP83826A 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

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 will 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 is only 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 2-10. A connection diagram for making measurements with the terminated cable is shown in Figure 2-11.

100Ω Terminated Cable for MDI Signal MeasurementFigure 2-10 100Ω Terminated Cable for MDI Signal Measurement
Connection Diagram for 100M Terminated CableFigure 2-11 Connection Diagram for 100M Terminated Cable

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 2-12 shows a link pulse.

DP83826A Link PulseFigure 2-12 DP83826A Link Pulse