SNLA423A March   2023  – June 2025 DP83826E , DP83826I

 

  1.   1
  2.   Trademarks
  3. 1DP83826 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
  7. 5Revision History

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 will only be available on the receive pair.

A short Ethernet cable terminated with 100 Ohm differential should 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.

DP83826 100 Ω Terminated Cable for MDI Signal MeasurementFigure 2-10 100 Ω Terminated Cable for MDI Signal Measurement
DP83826 Connection Diagram for 100 M Terminated Cable Figure 2-11 Connection Diagram for 100 M Terminated Cable

Auto-Negotation 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 16 ms. Figure 2-12 shows a link pulse.

DP83826 DP83826 Link Pulse Figure 2-12 DP83826 Link Pulse