Time domain reflectometry helps determine the
quality of the cable, connectors and terminations in addition to estimating OPEN and
SHORT faults along a cable. The DP83TC812-Q1
transmits a test pulse down
the attached twisted-pair cable. Transmitted pulses continue down the cable and
reflect from each imperfection and fault, allowing the device to measure the time to
return and strength (amplitude) of all reflections. This technique enables the DP83TC812-Q1 to identify cable OPENs and
TDR is activated by setting bit in register
0x1E. The procedure is as follows.
- Configure the DP83TC812-Q1 as per the initilization
settings from SNLA389 Application Note
- Ensure that the Link Partner connected to the PHY is slient. Link will be down
during TDR execution.
- Run the Pre-TDR configuration settings as listed in SNLA389.
- Start TDR by setting register 0x1E to '1'.
- Wait 100ms, read register 0x1E[1:0]
- If it reads 0b10 then TDR has executed successfully.
- If TDR executed successfully then read register 0x310 to get TDR results.
- 0x310: 0 = Half Wire Open not detected or 1 = Half Wire Open
- 0x310: 0 = Cable fault not detected or 1 = Cable fault detected
- 0x310: 0 = Cable fault
is OPEN or 1 = Cable fault is SHORT
- If valid cable fault is
detected then 0x310[5:0] will store the location value in meters.