KSZ8001SLI Micrel Semiconductor, Inc., KSZ8001SLI Datasheet - Page 23

• Manufacturer Part Number: KSZ8001SLI
• Description: 1.8V, 3.3V 10/100BASE-T/TX/F Physical Layer Transceiver
• Manufacturer: Micrel Semiconductor, Inc.

March 2006
Micrel
LinkMD Cable Diagnostics
The KSZ8001 utilizes time domain reflectometry (TDR) to analyze the cabling plant for common cabling problems such as open
circuits, short circuits and impedance mismatches. LinkMD works by sending a pulse of known amplitude and duration down the
MDI and MDIX pairs and analyzing the shape of the reflected signal. Timing the duration gives an indication of the distance to the
cabling fault with maximum distance of 200 m and accuracy of +/- 2 m. Cable diagnostics are only valid for copper connections and
do not support fiber optic operation.
LinkMD is used by accessing register 1dh, the LinkMD Control/Status register in conjunction with register 1fh, the 100BASE-TX PHY
Controller register. To use LinkMD, HP Auto-MDIX is disabled by writing a ‘1’ to 1f:13 to enable manual control over which pair is
used to transmit the LinkMD pulse. The self-clearing Cable diagnostic test enable bit, 1d.15 is set to ‘1’ to start the test on this pair.
When 1d.15 returns to ‘0’, the test is complete. The test result is returned in 1d.14:13 and the distance is returned in 1d.8:0. The
cable diagnostic test results are as follows:
The ‘11’ case, Invalid test, occurs when it is not possible for the KSZ8001 to shut down the link partner. In this case, the test is not
run, since it would not be possible for the KSZ8001 to determine if the detected signal is a reflection of the signal generated or a
signal from another source.
Cable length can be determined by multiplying the contents of 1d.8:0 by 0.39. This constant may be calibrated for different cabling
conditions, including cables with a velocity of propagation that varies significantly from the norm.
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•
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00 = Valid test, normal condition
01 = Valid test, open circuit in cable
10 = Valid test, short circuit in cable
11 = Invalid test, LinkMD failed
To the SD pin of the
Fiber Module
Rx +/-
Tx +/-
FTx
FRx
Pin
34
KSZ8001
KSZ8001
(Fiber Mode)
23
Ref_CLK
Ref_CLK
21 22
21 22
TxC/
Pin
Pin
TxC/
Vcc
TxD
RxD
Vcc
TxD
RxD
50 MHz
OSC
Revision 1.03
KSZ8001