DP83848H datasheet(16/78 Pages) NSC

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2.1.3 Auto-Negotiation Parallel Detection

The DP83848H supports the Parallel Detection function as

defined in the IEEE 802.3u specification. Parallel Detection

requires both the 10 Mb/s and 100 Mb/s receivers to moni-

tor the receive signal and report link status to the Auto-

Negotiation function. Auto-Negotiation uses this informa-

tion to configure the correct technology in the event that the

Link Partner does not support Auto-Negotiation but is

transmitting link signals that the 100BASE-TX or 10BASE-

T PMAs recognize as valid link signals.

If the DP83848H completes Auto-Negotiation as a result of

Parallel Detection, bit 5 or bit 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 deter-

mine 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 sin-

gle good link occurs then the parallel detect fault bit will be

set.

2.1.4 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 configu-

ration for the link. This function ensures that a valid config-

uration is maintained if the cable becomes disconnected.

A renegotiation request from any entity, such as a manage-

ment agent, will cause the DP83848H 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

DP83848H

will

resume

Auto-Negotiation

after

the

break_link_timer has expired by issuing FLP (Fast Link

Pulse) bursts.

2.1.5 Enabling Auto-Negotiation via Software

It is important to note that if the DP83848H has been initial-

ized upon power-up as a non-auto-negotiating device

(forced technology), and it is then required that Auto-Nego-

tiation or re-Auto-Negotiation be initiated via software,

bit 12 (Auto-Negotiation Enable) of the Basic Mode Control

Auto-Negotiation function to take effect.

2.1.6 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 com-

plete, 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-Negotia-

tion.

2.2 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 ran-

dom 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 (0x19h) 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 (0x19h) register.

Note: Auto-MDIX will not work in a forced mode of opera-

tion.

DP83848H Datasheet(PDF) 16 Page - National Semiconductor (TI)

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