The DP83826 can support 150 meter and above cable reach. Long cable reach causes the transmitted signal to face higher attenuation with cable length, so the gain and other settings need to be tweaked with cable length to achieve reliable fault detection using TDR. The cable is assumed to be divided into the following five segments:

• Segment 1: 0 m to 10 m
• Segment 2: 10 m to 20 m
• Segment 3: 20 m to 40 m
• Segment 4: 40 m to 80 m
• Segment 5: 80 m to 190 m

In order to a run complete TDR simulation, data from all five segments must be collected. Each segment requires a different set of register writes and segment 1 requires two register writes.

A fault can only be detected by the PHY's TDR if a fault (open or short) is introduced to the circuit. Follow these steps to run TDR:

1. Configure registers 0x170, 0x173, 0x175, 0x178, 0x416, 0x411, 0x456, and 0x1E to the corresponding values for Segment 1A shown in the Table 2-1. The registers used for configuration are extended registers. To configure extended registers, see the DP83826 Deterministic, Low-Latency, Low-Power, 10/100 Mbps, Industrial Ethernet PHY, data sheet for more information.
2. Confirm that TDR has finished running for that segment by checking 0x001E[1] = 1.
3. Read registers 0x180, 0x185, and 0x18A and fill out the corresponding row of the Table 2-5. The order of the rows of the table does not correspond to the order of the segments.
4. Repeat Step 1, 2 and 3 for segments 1B, 2, 3, 4, and 5 in that order. You may choose to only run TDR for certain segments. For instance, if your cable is 20m, you may fill out the rows for Segment 4 and 5 with zeros.
5. Process the data collected using the TDR Algorithm described in the next section to determine the fault location and type.