DP83848M datasheet(16/72 Pages) NSC

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2.1.2 Auto-Negotiation Register Control

When Auto-Negotiation is enabled, the DP83848M/J

transmits the abilities programmed into the Auto-Negotia-

tion Advertisement register (ANAR) at address 04h via

FLP Bursts. Any combination of 10 Mb/s, 100 Mb/s, Half-

Duplex, and Full Duplex modes may be selected.

Auto-Negotiation Priority Resolution:

— (1) 100BASE-TX Full Duplex (Highest Priority)

— (2) 100BASE-TX Half Duplex

— (3) 10BASE-T Full Duplex

— (4) 10BASE-T Half Duplex (Lowest Priority)

The Basic Mode Control Register (BMCR) at address 00h

provides control for enabling, disabling, and restarting the

Auto-Negotiation process. When Auto-Negotiation is dis-

abled, the Speed Selection bit in the BMCR controls

switching between 10 Mb/s or 100 Mb/s operation, and

the Duplex Mode bit controls switching between full

duplex operation and half duplex operation. The Speed

Selection and Duplex Mode bits have no effect on the

mode of operation when the Auto-Negotiation Enable bit

is set.

The Link Speed can be examined through the PHY Status

achieved.

The Basic Mode Status Register (BMSR) indicates the set

of available abilities for technology types, Auto-Negotia-

tion ability, and Extended Register Capability. These bits

are permanently set to indicate the full functionality of the

DP83848M/J (only the 100BASE-T4 bit is not set since

the DP83848M/J does not support that function).

The BMSR also provides status on:

— Completion of Auto-Negotiation

— Occurrence of a remote fault as advertised by the Link

Partner

— Establishment of a valid link

— Support for Management Frame Preamble suppression

The Auto-Negotiation Advertisement Register (ANAR)

indicates the Auto-Negotiation abilities to be advertised by

the DP83848M/J. All available abilities are transmitted by

default, but any ability can be suppressed by writing to the

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:

— Occurrence of a Parallel Detect Fault

— Next Page function support by the Link Partner

— Next page support function by DP83848M/J

— Reception of the current page that is exchanged by

Auto-Negotiation

— Auto-Negotiation support by the Link Partner

2.1.3 Auto-Negotiation Parallel Detection

The DP83848M/J 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 receiv-

ers 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 DP83848M/J completes Auto-Negotiation as a result

of Parallel Detection, bit 5 or bit 7 within the ANLPAR reg-

ister 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 DP83848M/J 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 DP83848M/J will resume Auto-Negoti-

ation 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.

DP83848M Datasheet(PDF) 16 Page - National Semiconductor (TI)

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