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2.1.3 Auto-Negotiation Parallel Detection

The DP83848J supports the Parallel Detection function as

defined in the IEEE 802.3u specification. Parallel Detec-

tion requires both the 10 Mb/s and 100 Mb/s receivers to

monitor the receive signal and report link status to the

Auto-Negotiation function. Auto-Negotiation uses this

information to configure the correct technology in the

event that the Link Partner does not support Auto-Negoti-

ation but is transmitting link signals that the 100BASE-TX

or 10BASE-T PMAs recognize as valid link signals.

If the DP83848J completes Auto-Negotiation as a result of

Parallel Detection, bit 5 or bit 7 within the ANLPAR regis-

ter 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 Detec-

tion 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.

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-Negotia-

tion 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 discon-

nected.

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

agement agent, will cause the DP83848J 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-Negotia-

tion resumes. The DP83848J will resume Auto-Negotia-

tion after the break_link_timer has expired by issuing FLP

(Fast Link Pulse) bursts.

2.1.5 Auto-Negotiation Complete Time

Parallel detection and Auto-Negotiation take approxi-

mately 2-3 seconds to complete. In addition, Auto-Negoti-

ation 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-Negoti-

ation.

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 appropri-

ate MDI pair for MDI/MDIX operation. The function uses a

random seed to control switching of the crossover cir-

cuitry. This implementation complies with the correspond-

ing

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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