Datasheet

 2017 Microchip Technology Inc. DS00002436B-page 29
KSZ8041TL/FTL/MLL
3.17.2 CROSSOVER CABLE
A crossover cable connects an MDI device to another MDI device, or an MDI-X device to another MDI-X device.
Figure 3-5 shows a typical crossover cable connection between two switches or hubs (two MDI-X devices).
3.18 LinkMD
®
Cable Diagnostics
The LinkMD
®
feature utilizes time domain reflectometry (TDR) to analyze the cabling plant for common cabling prob-
lems, 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 analyzing
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 computes the TDR information and presents it in a
user-readable digital format.
Cable diagnostics are only valid for copper connections and do not support fiber optic operation.
3.18.1 ACCESS
LinkMD is initiated by accessing register 1Dh, the LinkMD Control/Status Register, in conjunction with register 1Fh, the
PHY Control 2 Register.
3.18.2 USAGE
The following test procedure demonstrates how to use LinkMD for cable diagnostic:
1. Disable auto MDI/MDI-X by writing a ‘1’ to register 1Fh bit 13 to enable manual control over the differential pair
used to transmit the LinkMD pulse.
2. Select the differential pair to transmit the LinkMD pulse with register 1Fh bit 14.
3. Start cable diagnostic test by writing a ‘1’ to register 1Dh bit 15. This enable bit is self-clearing.
FIGURE 3-5: TYPICAL CROSSOVER CABLE CONNECTION
Receive Pair Receive Pair
Transmit Pair
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Transmit Pair
10/100 Ethernet
Media Dependent Interface
10/100 Ethernet
Media Dependent Interface
Modular Connector (RJ-45)
HUB
(Repeater or Switch)
Modular Connector (RJ-45)
HUB
(Repeater or Switch)
Crossover
Cable