LAN9250 datasheet(227/421 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

DS00001913A-page 227

LAN9250

12.2.14.2

Matched Cable Diagnostics

Matched cable diagnostics enable cable length estimation on 100 Mbps-linked cables of up to 120 meters. If there is an

active 100 Mb link, the approximate distance to the link partner can be estimated using the PHY Cable Length Register

(PHY_CABLE_LEN). If the cable is properly terminated, but there is no active 100 Mb link (the link partner is disabled,

nonfunctional, the link is at 10 Mb, etc.), the cable length cannot be estimated and the PHY Cable Length Register

(PHY_CABLE_LEN) should be ignored. The estimated distance to the link partner can be determined via the Cable

Length (CBLN) field of the PHY Cable Length Register (PHY_CABLE_LEN) using the lookup table provided in Table 12-

7. The typical cable length measurement margin of error for a matched cable case is +/- 20 m. The matched cable length

margin of error is consistent for all cable types from 0 to 120 m.

CAT 6 Cable, 101-160 m

CAT 5E Cable, 101-160 m

CAT 5 Cable, 101-160 m

TABLE 12-6:

TYPICAL MEASUREMENT ERROR FOR SHORTED CABLE (+/- METERS)

PHYSICAL DISTANCE

TO FAULT

SELECTED PROPAGATION CONSTANT

PSHORT =

Unknown

PSHORT =

CAT 6

PSHORT =

CAT 5E

PSHORT =

CAT 5

CAT 6 Cable, 0-100 m

CAT 5E Cable, 0-100 m

CAT 5 Cable, 0-100 m

CAT 6 Cable, 101-160 m

CAT 5E Cable, 101-160 m

CAT 5 Cable, 101-160 m

TABLE 12-7:

MATCH CASE ESTIMATED CABLE LENGTH (CBLN) LOOKUP

CBLN Field Value

Estimated Cable Length

0 - 3

517

627

738

849

959

TABLE 12-5:

TYPICAL MEASUREMENT ERROR FOR OPEN CABLE (+/- METERS)

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