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KSZ8873MLLJ Datasheet(PDF) 22 Page - Micrel Semiconductor

Part No. KSZ8873MLLJ
Description  Integrated 3-Port 10/100 Managed Switch with PHYs
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Maker  MICREL [Micrel Semiconductor]
Homepage  http://www.micrel.com
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KSZ8873MLLJ Datasheet(HTML) 22 Page - Micrel Semiconductor

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Micrel, Inc.
KSZ8873MLLJ
September 2011
22
M9999-091911-1.8
LinkMD
® Cable Diagnostics
KSZ8873MLLJ supports the LinkMD
®. 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. 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 the PHY special control/status registers {26, 42} and the LinkMD result registers {27, 43}
for ports 1 and 2 respectively; and in conjunction with the port registers control 13 for ports 1and 2 respectively to disable
Auto MDI/MDIX.
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 {42,43,45} on port 2.
1. Disable auto MDI/MDI-X by writing a ‘1’ to register 45, 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 42, bit [4]. This enable bit is self-clearing.
3. Wait (poll) for register 42, bit [4] to return a ‘0’, indicating cable diagnostic test is completed.
4. Read cable diagnostic test results in register 42, 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 KSZ8873MLLJ is unable to shut down the link partner. In this instance,
the test is not run, since it would be impossible for the KSZ8873MLLJ 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 42, bit [0] and register 43, 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) = 0.4 x {(register 26, bit [0]),(register 27, bits [7:0])}
D (distance to cable fault) is expressed in meters.
Concatenated value of registers 42 and 43 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.
Functional Overview: Power Management
The KSZ8873MLLJ supports enhanced power management feature in low power state with energy detection to ensure
low-power dissipation during device idle periods. There are five operation modes under the power management function
which is controlled by two bits in Register 195 (0xC3) and one bit in Register 29 (0x1D),45(0x2D) as shown below:
Register 195 bit[1:0] = 00 Normal Operation Mode
Register 195 bit[1:0] = 01 Energy Detect Mode
Register 195 bit[1:0] = 10 Soft Power Down Mode
Register 195 bit[1:0] = 11 Power Saving Mode
Register 29,45 bit 3 =1 Port Based Power Down Mode
Table 3 indicates all internal function blocks status under four different power management operation modes.


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