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ANAR. Updating the ANAR to suppress an ability is one

way for a management agent to change (restrict) the tech-

nology that is used.

The

Auto-Negotiation

Link

Partner

Ability

(ANLPAR) at address 05h is used to receive the base link

code word as well as all next page code words during the

negotiation. Furthermore, the ANLPAR will be updated to

either 0081h or 0021h for parallel detection to either 100

Mb/s or 10 Mb/s respectively.

The Auto-Negotiation Expansion Register (ANER) indi-

cates additional Auto-Negotiation status. The ANER pro-

vides status on:

— Whether or not a Parallel Detect Fault has occurred

— Whether or not the Link Partner supports the Next Page

function

— Whether or not the DP83848C supports the Next Page

function

— Whether or not the current page being exchanged by

Auto-Negotiation has been received

— Whether or not the Link Partner supports Auto-Negotia-

tion

2.1.3 Auto-Negotiation Parallel Detection

The DP83848C 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 DP83848C 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 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 DP83848C 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

DP83848C

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 DP83848C 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.

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