SNLS779A July 2025 – November 2025 DP83TC815-Q1
PRODUCTION DATA
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 DP83TC815-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 DP83TC815-Q1 to identify cable OPENs and SHORTs.
TDR is activated by setting bit[15] in register 0x1E. The procedure is outlined in Table 7-17. Note that the Link Partner connected to the PHY must be silent. Link is down during TDR execution.
| SEQUENCE | DESCRIPTION | REGISTER READ/WRITE | |
|---|---|---|---|
| Step 1: For DP83TC815-Q1 as leader |
Force the link-down by writing register and enable link-partner to go silent. In case of valid open and short cable faults, TDR still functions well without step 1. For good cable case, TDR register 0x001E can show Fail on bypassing this step. | Write Reg[0x1834] = 0x8001 To make leader go silent. | |
| Step 1: ForDP83TC815-Q1as follower |
Force the link-down by writing register and enable link-partner to go silent. In case of valid open and short cable faults, TDR still works fine without step 1. For good cable case, TDR register 0x001E can show Fail on bypassing this step. | If DP83TC815-Q1 is link partner, write reg[0x1834] = 0x8001 on the link partner to make it silent. If other PHY is used, contact the vendor for register write to make link partner silent | |
| Step 2 | TDR configuration: Pre-run | Reg[0x0523] =
0x0001 Reg[0x04DF] = 0x0003 Reg[0x0827] = 0x3800 Reg[0x0301] = 0x1700 Reg[0x0302] = 0x0045 Reg[0x0303] = 0x042D Reg[0x0304] = 0x0026 Reg[0x0305] = 0x0015 Reg[0x001F] = 0x4000 Reg[0x0523] = 0x0000 Reg[0x001F] = 0x0000 Reg[0x001E]= 0x8000 |
|
| Step 3 | Start TDR | Reg[0x001E(15)] = 1 | |
| Step 4 | Wait for 100ms (must be sufficient for TDR to converge for maximum cable length) | ||
| Step 5 | Read 0x001E[1:0] = [TDR done : TDR fail]. Value must be [1,0]. Fault type and locations are valid only if this correct value is read. Value other than [1,0] means that there is some noise on the line which is causing TDR to fail. | ||
| Step 6 | Fault type and location is read. | Read Reg 0x0310 for fault status and fault type. For fault types: | |
| TDR_TC-1 Reg 0x0310[7] = peak_detect | |||
| 0b | Fault not detected | ||
| 1b | Fault detected | ||
| TDR_TC-1 Reg 0x0310[6] = peak_sign | |||
| 0b | short | ||
| 1b | open | ||
| **peak_sign only valid if Fault detected in cable. If a valid fault detected: register 0x0310[5:0] = is the fault location in meters. | |||