Datasheet

DP83848VYB

SNLS266D –MAY 2007–REVISED APRIL 2013

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If the DP83848VYB completes Auto-Negotiation as a result of Parallel Detection, bits 5 and 7 within the

ANLPAR register will be set to reflect the mode of operation present in the Link Partner. Note that bits 4:0

of the ANLPAR will also be set to 00001 based on a successful parallel detection to indicate a valid 802.3

selector field. Software may determine that negotiation completed via Parallel Detection by reading a zero

in the Link Partner Auto-Negotiation Able bit once the Auto-Negotiation Complete bit is set. If configured

for parallel detect mode and any condition other than a single good link occurs then the parallel detect

fault bit will be set.

5.1.4 Auto-Negotiation Restart

Once Auto-Negotiation has completed, it may be restarted at any time by setting bit 9 (Restart Auto-

Negotiation) of the BMCR to one. If the mode configured by a successful Auto-Negotiation loses a valid

link, then the Auto-Negotiation process will resume and attempt to determine the configuration for the link.

This function ensures that a valid configuration is maintained if the cable becomes disconnected.

A renegotiation request from any entity, such as a management agent, will cause the DP83848VYB to halt

any transmit data and link pulse activity until the break_link_timer expires (~1500 ms). Consequently, the

Link Partner will go into link fail and normal Auto-Negotiation resumes. The DP83848VYB will resume

Auto-Negotiation after the break_link_timer has expired by issuing FLP (Fast Link Pulse) bursts.

5.1.5 Enabling Auto-Negotiation via Software

It is important to note that if the DP83848VYB has been initialized upon power-up as a non-auto-

negotiating device (forced technology), and it is then required that Auto-Negotiation or re-Auto-Negotiation

be initiated via software, bit 12 (Auto-Negotiation Enable) of the Basic Mode Control Register (BMCR)

must first be cleared and then set for any Auto-Negotiation function to take effect.

5.1.6 Auto-Negotiation Complete Time

Parallel detection and Auto-Negotiation take approximately 2-3 seconds to complete. In addition, Auto-

Negotiation with next page should take approximately 2-3 seconds to complete, depending on the number

of next pages sent.

Refer to Clause 28 of the IEEE 802.3u standard for a full description of the individual timers related to

Auto-Negotiation.

5.2 AUTO-MDIX

When enabled, this function utilizes Auto-Negotiation to determine the proper configuration for

transmission and reception of data and subsequently selects the appropriate MDI pair for MDI/MDIX

operation. The function uses a random seed to control switching of the crossover circuitry. This

implementation complies with the corresponding IEEE 802.3 Auto-Negotiation and Crossover

Specifications.

Auto-MDIX is enabled by default and can be configured via strap or via PHYCR (19h) register, bits [15:14].

Neither Auto-Negotiation nor Auto-MDIX is required to be enabled in forcing crossover of the MDI pairs.

Forced crossover can be achieved through the FORCE_MDIX bit, bit 14 of PHYCR (19h) register.

NOTE

Auto-MDIX will not work in a forced mode of operation.

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