DP83867CS datasheet(35/129 Pages) TI2

35 / 129 page

7.4.5 BIST Configuration

The device incorporates an internal PRBS Built-in Self Test (BIST) circuit to accommodate in-circuit testing or

diagnostics. The BIST circuit can be used to test the integrity of the transmit and receive data paths. The BIST

can be performed using both internal loopback (digital or analog) or external loopback using a cable fixture. The

BIST simulates pseudo-random data transfer scenarios in format of real packets and Inter-Packet Gap (IPG) on

the lines.

The BIST is implemented with independent transmit and receive paths, with the transmit block generating a

continuous stream of a pseudo-random sequence. The device generates a 15-bit pseudo-random sequence for

the BIST. The received data is compared to the generated pseudo-random data by the BIST Linear Feedback

Shift Register (LFSR) to determine the BIST pass or fail status. The number of error bytes that the PRBS

checker received is stored in the BICSR2 register (0x0072). The status of whether the PRBS checker is locked

to the incoming receive bit stream, whether the PRBS has lost sync, and whether the packet generator is busy,

can be read from the STS2 register (0x0017h). While the lock and sync indications are required to identify the

beginning of proper data reception, for any link failures or data corruption, the best indication is the contents of

the error counter in the BICSR2 register (0x0072). The number of received bytes are stored in BICSR1 (0x0071).

The PRBS test can be put in a continuous mode by using bit 14 of the BISCR register (0x0016h). In continuous

mode, when one of the PRBS counters reaches the maximum value, the counter starts counting from zero

again. Packet transmission can be configured for one of two types, 64 and 1518 bytes, through register bit 13 of

the BISCR register (0x0016).

7.4.6 Cable Diagnostics

With the vast deployment of Ethernet devices, the need for reliable, comprehensive and user-friendly cable

diagnostic tool is more important than ever. The wide variety of cables, topologies, and connectors deployed

results in the need to non-intrusively identify and report cable faults. The TI cable-diagnostic unit provides

extensive information about cable integrity. The DP83867 offers, Time Domain Reflectometry (TDR) capability in

the Cable Diagnostic tools kit.

7.4.6.1 TDR

The DP83867 uses Time Domain Reflectometry (TDR) to determine the quality of the cables, connectors, and

terminations in addition to estimating the cable length. Some of the possible problems that can be diagnosed

include opens, shorts, cable impedance mismatch, bad connectors, termination mismatches, cross faults, cross

shorts, and any other discontinuities along the cable.

The DP83867 transmits a test pulse of known amplitude (1V or 2.5V) down each of the two pairs of an attached

cable. The transmitted signal continues down the cable and reflects from each cable imperfection, fault, bad

connector, and from the end of the cable. After the pulse transmission, the DP83867 measures the return time

and amplitude of all these reflected pulses. This technique enables measuring the distance and magnitude

(impedance) of non-terminated cables (open or short), discontinuities (bad connectors), improperly-terminated

cables, and crossed pairs wires with ±1m accuracy.

The DP83867 also uses data averaging to reduce noise and improve accuracy. The DP83867 can record up to

five reflections within the tested pair. If more than 5 reflections are recorded, the DP83867 saves the first 5 of

them. If a cross fault is detected, the TDR saves the first location of the cross fault and up to 4 reflections in the

tested channel. The DP83867 TDR can measure cables beyond 100m in length.

For all TDR measurements, the transformation between time of arrival and physical distance is done by the

external host using minor computations (such as multiplication, addition, and lookup tables). The host must know

the expected propagation delay of the cable, which depends, among other things, on the cable category (for

example, CAT5, CAT5e, or CAT6).

TDR measurement is allowed in the DP83867 in the following scenarios:

• While Link partner is disconnected – cable is unplugged at the other side

• Link partner is connected but remains quiet (for example, in power-down mode)

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DP83867CS, DP83867IS, DP83867E

SNLS504F – OCTOBER 2015 – REVISED JANUARY 2025

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