DP83620SQ Datasheet, PDF (41/105 Pages) Texas Instruments – DP83620 Industrial Temperature Single Port 10/100 Mbps Ethernet Physical Layer

DP83620
www.ti.com
SNLS339C – JANUARY 2011 – REVISED APRIL 2013
5.11.2.2 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.
5.11.2.3 Threshold Control
The LQDR (1Eh) register also provides a method of programming high and low thresholds for each of the
five 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 minimum or maximum values. Table 5-4 shows the five parameters and range of
values:
Parameter
DEQ_C1
DAGC
DBLW
Frequency Offset
Frequency Control
SNR Variance
Table 5-4. Link Quality Monitor Parameter Ranges
Minimum Value
-128
0
-128
-128
-128
0
Maximum Value
+127
+255
+127
+127
+127
+2304
Min (2-s comp)
0x80
0x00
0x80
0x80
0x80
0x0000
Max (2-s comp)
0x7F
0xFF
0x7F
0x7F
0x7F
0x900
Note that values are signed 2-s complement values except for DAGC and Variance which are always
positive. The maximum SNR Variance is calculated by assuming the worst-case squared error (144) is
accumulated every 8 ns for 8*2²⁰ ns (roughly 8 ms or exactly 1,048,576 clock cycles).
For example, to set the DBLW Low threshold to -38:
1. Write 14DAh to LQDR to set the Write_LQ_Thr bit, select the DBLW Low Threshold, and write data of
-38 (0xDA).
2. Write 8000 to LQMR to enable the Link Quality Monitor (if not already enabled).
5.11.3 TDR Cable Diagnostics
The DP83620 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
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