This application note outlines how Time Domain Reflectometry (TDR) helps solving various kind of cable fault challenges of Ethernet based communication systems. The application note describes the procedure to use TDR feature of the DP83867 and the DP83869 for implementing cable diagnostics feature in system.
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TDR only works for twisted pair connections. TDR involves sending a pulse on TX and RX pair and observing results on either pair. By measuring voltage amplitude, polarity, and the time interval, the PHY can determine the nature and position of the fault. The DP83867/DP83869 TDR generator sends pulse on the TX and RX channel, then monitors both channels to observe reflections. It sends a pulse one channel at a time, and if reflections are observed on the other channel, then the PHY TDR realizes that the wires have been crossed. The DP83867/DP83869 can detect one peak for each transmit and receive channel. TDR can be used for the following:
TDR can be used only when the Link is down.