KSZ8893-MQL Micrel Semiconductor, Inc., KSZ8893-MQL Datasheet - Page 27

• Manufacturer Part Number: KSZ8893-MQL
• Description: Integrated 3-Port 10/100 Managed Switch with PHYs
• Manufacturer: Micrel Semiconductor, Inc.

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.
Note: Cable diagnostics are only valid for copper connections and do not support fiber optic operation.
Access
LinkMD is initiated by accessing registers {26,27} and {42,43}, the LinkMD Control/Status registers, for ports 1
and 2, respectively; and in conjunction with registers 29 and 45, Port Control Register 13, for ports 1 and 2,
respectively.
Alternatively, the MIIM PHY registers 0 and 29 can be used for LinkMD access.
Usage
The following is a sample procedure for using LinkMD with registers {26,27,29} on port 1.
1. Disable auto MDI/MDI-X by writing a ‘1’ to register 29, bit [2] to enable manual control over the differential pair
2. Start cable diagnostic test by writing a ‘1’ to register 26, bit [4]. This enable bit is self-clearing.
3. Wait (poll) for register 26, bit [4] to return a ‘0’, indicating cable diagnostic test is completed.
4. Read cable diagnostic test results in register 26, bits [6:5]. The results are as follows:
5. Get distance to fault by concatenating register 26, bit [0] and register 27, bits [7:0]; and multiplying the result
For port 2 and for the MIIM PHY registers, LinkMD usage is similar.
Micrel
November 2005
used to transmit the LinkMD pulse.
The ‘11’ case, invalid test, occurs when the KSZ8893MQL is unable to shut down the link partner. In this
instance, the test is not run, since it would be impossible for the KSZ8893MQL to determine if the detected
signal is a reflection of the signal generated or a signal from another source.
by a constant of 0.4. The distance to the cable fault can be determined by the following formula:
D (distance to cable fault) is expressed in meters.
Concatenated value of registers 26 and 27 is 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.
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)
D (distance to cable fault) = 0.4 x {(register 26, bit [0]),(register 27, bits [7:0])}
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KSZ8893MQL/MQLI
M9999-111705