Datasheet

DP83849IF

SNOSAX8D –JUNE 2009–REVISED APRIL 2013

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Example: To generate an interrupt on a change of link status or on a change of energy detect power state,

the steps would be:

• Write 0003h to MICR to set INTEN and INT_OE

• Write 0060h to MISR to set ED_INT_EN and LINK_INT_EN

• Monitor PWRDOWN_INT pin

When PWRDOWN_INT pin asserts low, the user would read the MISR register to see if the ED_INT or

LINK_INT bits are set, i.e. which source caused the interrupt. After reading the MISR, the interrupt bits

should clear and the PWRDOWN_INT pin will deassert.

8.7 ENERGY DETECT MODE

When Energy Detect is enabled and there is no activity on the cable, the DP83849IF will remain in a low

power mode while monitoring the transmission line. Activity on the line will cause the DP83849IF to go

through a normal power up sequence. Regardless of cable activity, the DP83849IF will occasionally wake

up the transmitter to put ED pulses on the line, but will otherwise draw as little power as possible. Energy

detect functionality is controlled via register Energy Detect Control (EDCR), address 1Dh.

8.8 LINK DIAGNOSTIC CAPABILITIES

The DP83849IF contains several system diagnostic capabilities for evaluating link quality and detecting

potential cabling faults in Twisted Pair cabling. Software configuration is available through the Link

Diagnostics Registers - Page 2 which can be selected via Page Select Register (PAGESEL), address 13h.

These capabilities include:

• Linked Cable Status

• Link Quality Monitor

• TDR (Time Domain Reflectometry) Cable Diagnostics

8.8.1 Linked Cable Status

In an active connection with a valid link status, the following diagnostic capabilities are available:

• Polarity reversal

• Cable swap (MDI vs MDIX) detection

• 100Mb Cable Length Estimation

• Frequency offset relative to link partner

• Cable Signal Quality Estimation

8.8.1.1 Polarity Reversal

The DP83849IF detects polarity reversal by detecting negative link pulses. The Polarity indication is

available in bit 12 of the PHYSTS (10h) or bit 4 of the 10BTSCR (1Ah). Inverted polarity indicates the

positive and negative conductors in the receive pair are swapped. Since polarity is corrected by the

receiver, this does not necessarily indicate a functional problem in the cable.

Since the polarity indication is dependent on link pulses from the link partner, polarity indication is only

valid in 10Mb modes of operation, or in 100Mb Auto-Negotiated mode. Polarity indication is not available

in 100Mb forced mode of operation or in a parallel detected 100Mb mode.

8.8.1.2 Cable Swap Indication

As part of Auto-Negotiation, the DP83849IF has the ability (using Auto-MDIX) to automatically detect a

cable with swapped MDI pairs and select the appropriate pairs for transmitting and receiving data. Normal

operation is termed MDI, while crossed operation is MDIX. The MDIX status can be read from bit 14 of the

PHYSTS (10h).

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