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KSZ8765CLXCC View Datasheet(PDF) - Micrel

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KSZ8765CLXCC Datasheet PDF : 153 Pages
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Micrel, Inc.
KSZ8765CLX
LinkMD® Cable Diagnostics
The LinkMD® feature 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 MDI-X pairs and then analyzes the
shape of the reflected signal. Timing the pulse duration gives an indication of the distance to the cabling fault with
maximum distance of 200m and accuracy of ±2m. Internal circuitry displays the TDR information in a user-readable digital
format.
Please note that cable diagnostics are only valid for copper connections.
Access
LinkMD is initiated by accessing the PHY’s special control/status Registers {58, 74} and the LinkMD result Registers {59,
75} for Ports 3 and 4 respectively and in conjunction with the Port control 10 Register for Ports 3 and 4 respectively to
disable Auto-MDI/MDI-X.
Alternatively, the MIIM PHY Registers 0 and 1d can also be used for LinkMD access.
Usage
The following is a sample procedure for using LinkMD with Registers {58, 59, 61} on Port 3.
1. Disable Auto-MDI/MDI-X by writing a ‘1’ to Register 61, bit [2] to enable manual control over the differential pair used
to transmit the LinkMD pulse.
2. Start cable diagnostic test by writing a ‘1’ to Register 58, bit [4]. This enable bit is self-clearing.
3. Wait (poll) for Register 58, bit [4] to return a ‘0’, and indicating cable diagnostic test is completed.
4. Read cable diagnostic test results in Register 58, bits [6:5]. The results are as follows:
00 = normal condition (valid test)
01 = open condition detected in cable (valid test)
10 = short condition detected in cable (valid test)
11 = cable diagnostic test failed (invalid test)
The ‘11’ case, invalid test, occurs when the KSZ8765CLX is unable to shut down the link partner. In this instance, the
test is not run because it would be impossible for the KSZ8765CLX to determine if the detected signal is a reflection of
the signal generated or a signal from another source.
5. Get distance to fault by concatenating Register 58, bit [0] and Register 59, bits [7:0] and multiplying the result by a
constant of 0.4. The distance to the cable fault can be determined by the following formula:
D (distance to cable fault meter) = 0.4 x (Register 58, bit [0], Register 59, bits [7:0])
D (distance to cable fault) is expressed in meters.
Concatenated value of Registers 58 bit [0] and 59 bits [7:0] should be converted to decimal before multiplying by 0.4.
The constant (0.4) may be calibrated for different cabling conditions, including cables with a velocity of propagation that
varies significantly from the norm.
For Port 4 and using the MIIM PHY registers, LinkMD usage is similar.
July 23, 2014
24
Revision 1.0
 

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