Datasheet

KSZ8873MLL/FLL/RLL

DS00002348A-page 16  2017 Microchip Technology Inc.

FIGURE 3-3: AUTO-NEGOTIATION AND PARALLEL OPERATION

3.1.12 LINKMD

CABLE DIAGNOSTICS

KSZ8873MLL/FLL/RLL supports 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. Inter-

nal circuitry displays the TDR information in a user-readable digital format.

Cable diagnostics are only valid for copper connections and do not support fiber optic operation.

3.1.12.1 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 1 and 2 respectively to

disable Auto MDI/MDIX.

Alternatively, the MIIM PHY registers 0 and 29 can be used for LinkMD access.

3.1.12.2 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.

START AUTO-NEGOTIATION

FORCE LINK SETTING

LISTEN FOR 10BASE-T

LINK PULSES

LISTEN FOR 100BASE-TX

IDLES

ATTEMPT AUTO-

NEGOTIATION

LINK MODE SET

BYPASS AUTO-NEGOTIATION

AND SET LINK MODE

LINK MODE SET?

PARALLEL

OPERATION

YES

JOIN FLOW