LAN8804 datasheet(36/91 Pages) MICROCHIP

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LAN8804

DS00003591G-page 36

• Auto MDI/MDI-X disabled via the Digital Debug Control 1 Register

• Full Duplex set via the Basic Control Register

• Link Speed set to 1000Mbps via the Basic Control Register

• Master-Slave configuration set to Slave via the Auto Negotiation Master Slave Control Register

Wait 10ms prior to testing the pairs.

In this scenario, for each of the four twisted pairs, LinkMD will return Open or Short along with a distance, or Normal.

• Normal indicates a good cable which is properly terminated at the Link Partner. Due to no TDR reflections, no

cable distance is available with this result (VCT[7:0] is invalid).

• Open or Short indicates a bad cable or improper Link Partner termination. VCT[7:0] indicates the distance to the

cable fault.

After running the cable diagnostics, perform another software reset via the Basic Control Register.

5.7.3

LINKMD WITH PARTIALLY ACTIVE LINK PARTNER

In this scenario, the remote end of the cable is connected to a Link Partner. The Link Partner is powered up and in the

following state:

• Auto Negotiation may be enabled, disabled, or unknown

• Auto MDI/MDI-X is disabled, but we are able to selectively configure MDI or MDI-X, as required for the LinkMD

tests

Prior to running the cable diagnostics, perform a software reset via the Basic Control Register. After reset, the following

must be configured:

• Auto Negotiation disabled via the Digital Debug Control 1 Register

• Auto MDI/MDI-X disabled via the Digital Debug Control 1 Register

• Full Duplex set via the Basic Control Register

• Link Speed set to 1000Mbps via the Basic Control Register

• Master-Slave configuration set to Slave via the Auto Negotiation Master Slave Control Register

Wait 10ms prior to testing the pairs.

The LinkMD test is first run with the Link Partner in MDI mode on twisted pairs B, C, and D.

The LinkMD test is then run with the Link Partner in MDI-X mode on twisted pair A.

• Normal indicates a good cable which is properly terminated at the Link Partner. Due to no TDR reflections, no

cable distance is available with this result (VCT[7:0] is invalid).

• Open or Short indicates a bad cable or improper Link Partner termination. VCT[7:0] indicates the distance to the

cable fault.

After running the cable diagnostics, perform another software reset via the Basic Control Register.

APPLICATION NOTE: If the Cable Diagnostics Status (VCT_ST[1:0]) field indicates Failed, it is generally due to

multiple pulses being received after sending out a single pulse. In this Partially Active test,

the Link Partner is allowed to be in the Auto-Negotiation state, but if the Link Partner is

mistakenly in forced 1000BASE-T or 100BASE-TX mode, the test will fail.

APPLICATION NOTE: Any signal received from a link partner will interfere with the TDR test. Energy detection must

first be checked on each wire pair by using the procedure in Section 5.19.2, "Energy-Detect

Power-Down Mode".

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