Datasheet

DP83849IF

SNOSAX8D –JUNE 2009–REVISED APRIL 2013

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To allow the Link Quality Monitor to interrupt the system, the Interrupt must be enabled through the

interrupt control registers, MICR (11h) and MISR (12h).

8.8.2.2 Checking Current Parameter Values

Prior to setting Threshold values, it is recommended that software check current adapted values. The

thresholds may then be set relative to the adapted values. The current adapted values can be read using

the LQDR register by setting the Sample_Param bit [13] of LQDR, address (1Eh).

For example, to read the DBLW current value:

1. Write 2400h to LQDR (1Eh) to set the Sample_Param bit and set the LQ_PARAM_SEL[2:0] to 010.

2. Read LQDR (1Eh). Current DBLW value is returned in the low 8 bits.

8.8.2.3 Threshold Control

The LQDR (1Eh) register also provides a method of programming high and low thresholds for each of the

four parameters that can be monitored. The register implements an indirect read/write mechanism.

Writes are accomplished by writing data, address, and a write strobe to the register. Reads are

accomplished by writing the address to the register, and reading back the value of the selected threshold.

Setting thresholds to the maximum or minimum values will disable the threshold comparison since values

have to exceed the threshold to generate a warning condition.

Warnings are not generated if the parameter is equal to the threshold. By default, all thresholds are

disabled by setting to the min or max values. The following table shows the four parameters and range of

values:

Table 8-4. Link Quality Monitor Parameter Ranges

Parameter Minimum Value Maximum Value Min (2-s comp) Max (2-s comp)

DEQ C1 -128 +127 0x80 0x7F

DAGC 0 +255 0x00 0xFF

DBLW -128 +127 0x80 0x7F

Freq Offset -128 +127 0x80 0x7F

Freq Control -128 +127 0x80 0x7F

8.8.3 TDR Cable Diagnostics

The DP83849IF implements a Time Domain Reflectometry (TDR) method of cable length measurement

and evaluation which can be used to evaluate a connected twisted pair cable. The TDR implementation

involves sending a pulse out on either the Transmit or Receive conductor pair and observing the results

on either pair. By observing the types and strength of reflections on each pair, software can determine the

following:

• Cable short

• Cable open

• Distance to fault

• Identify which pair has a fault

• Pair skew

The TDR cable diagnostics works best in certain conditions. For example, an unterminated cable provides

a good reflection for measuring cable length, while a cable with an ideal termination to an unpowered

partner may provide no reflection at all.

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