Datasheet

DP83630

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SNLS335B –OCTOBER 2010–REVISED APRIL 2013

5.11 LINK DIAGNOSTIC CAPABILITIES

The DP83630 contains several system diagnostic capabilities for evaluating link quality and detecting

potential cabling faults in twisted pair cabling. Software configuration is available through the Link

Diagnostics Registers - Page 2 which can be selected via Page Select Register (PAGESEL), address 13h.

These capabilities include:

— Linked Cable Status

— Link Quality Monitor

— TDR (Time Domain Reflectometry) Cable Diagnostics

5.11.1 Linked Cable Status

In an active connection with a valid link status, the following diagnostic capabilities are available:

— Polarity reversal

— Cable swap (MDI vs MDIX) detection

— 100 Mb Cable Length Estimation

— Frequency offset relative to link partner

— Cable Signal Quality Estimation

5.11.1.1 Polarity Reversal

The DP83630 detects polarity reversal by detecting negative link pulses. The Polarity indication is

available in bit 12 of the PHYSTS (10h) or bit 4 of the 10BTSCR (1Ah). Inverted polarity indicates the

positive and negative conductors in the receive pair are swapped. Since polarity is corrected by the

receiver, this does not necessarily indicate a functional problem in the cable.

Since the polarity indication is dependent on link pulses from the link partner, polarity indication is only

valid in 10 Mb modes of operation, or in 100 Mb Auto-Negotiated mode. Polarity indication is not available

in 100 Mb forced mode of operation or in a parallel detected 100 Mb mode.

5.11.1.2 Cable Swap Indication

As part of Auto-Negotiation, the DP83630 has the ability (using Auto-MDIX) to automatically detect a cable

with swapped MDI pairs and select the appropriate pairs for transmitting and receiving data. Normal

operation is termed MDI, while crossed operation is MDIX. The MDIX status can be read from bit 14 of the

PHYSTS (10h).

5.11.1.3 100 Mb Cable Length Estimation

The DP83630 provides a method of estimating cable length based on electrical characteristics of the 100

Mb link. This essentially provides an effective cable length rather than a measurement of the physical

cable length. The cable length estimation is only available in 100 Mb mode of operation with a valid link

status. The cable length estimation is available at the Link Diagnostics Registers - Page 2, register 100

Mb Length Detect (LEN100_DET), address 14h.

5.11.1.4 Frequency Offset Relative to Link Partner

As part of the 100 Mb clock recovery process, the DSP implementation provides a frequency control

parameter. This value may be used to indicate the frequency offset of the device relative to the link

partner. This operation is only available in 100 Mb operation with a valid link status. The frequency offset

can be determined using the register 100 Mb Frequency Offset Indication (FREQ100), address 15h, of the

Link Diagnostics Registers - Page 2.

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