DP83840AVCE datasheet(39/91 Pages) TI1

39 / 91 page

3.0 Functional Description (Continued)

National Semiconductor

Version A

The Basic Mode Status Register (BMSR) at address 01h

indicates the set of available abilities for technology types

(bits 15 to 11, register address 01h), Auto-Negotiation

ability (bit 3, register address 01h), and Extended Register

Capability (bit 0, register address 01h). These bits are

permanently set to indicate the full functionality of the

DP83840A (only the 100BASE-T4 bit is not set since the

DP83840A does not support that function, while it does

support all the other functions).

The BMSR also provides status on:

1. Whether Auto-Negotiation is complete (bit 5, register

address 01h)

2. Whether the Link Partner is advertising that a remote

fault has occurred (bit 4, register address 01h)

3. Whether a valid link has been established (bit 2, regis-

ter address 01h)

4. Support for Management Frame Preamble suppres-

sion (bit 6, register address 01h)

The Auto-Negotiation Advertisement Register (ANAR) at

address 04h indicates the Auto-Negotiation abilities to be

advertised by the DP83840A. 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

(force) the technology that is used.

The

Auto-Negotiation

Link

Partner

Ability

(ANLPAR) at address 05h indicates the abilities of the Link

Partner as indicated by Auto-Negotiation communication.

The contents of this register are considered valid when the

Auto-Negotiation Complete bit (bit 5, register address 01h)

is set.

The Auto-Negotiation Expansion Register (ANER) at

address 06h indicates additional Auto-Negotiation status.

The ANER provides status on:

1. Whether a Multiple Link Fault has occurred (bit 4, reg-

ister address 06h)

2. Whether the Link Partner supports the Next Page func-

tion (bit 3, register address 06h)

3. Whether the DP83840A supports the Next Page func-

tion (bit 2, register address 06h). The DP83840A does

not support the Next Page function.

4. Whether the current page being exchanged by Auto-

Negotiation has been received (bit1, register address

06h)

5. Whether the Link Partner supports Auto-Negotiation

(bit 0, register address 06h)

3.9.3 Auto-Negotiation Parallel Detection

The

DP83840A

conjunction

with

the

DP83223

transceiver 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

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-Negotiation yet

is transmitting link signals that the 100BASE-X or 10BASE-

T PMAs recognize as valid link signals.

The Auto-Negotiation function will only accept a valid link

signal for the purpose of Parallel Detection from PMAs

which have a corresponding bit set in the Auto-Negotiation

Advertisement register, (ANAR register bits 5 and 7,

conﬁgured as a 100 Mb/s only, 10 Mb/s only, or 10 Mb/s &

100 Mb/s CSMA/CD operation device depending on the

advertised abilities. The state of these bits may be modiﬁed

via the AN0 and AN1 pins (see 3.9.1 Auto-Negotiation Pin

Control) or by writing to the ANAR. For example, if bit 5 is

zero and bit 7 is one in the ANAR (i.e. 100 Mb/s CSMA/CD

only), and the Link Partner is 10BASE-T without Auto-

Negotiation, then Auto-Negotiation will not complete since

the advertised abilities and the detected abilities have no

common mode. This operation allows the DP83840A to be

used in single mode (i.e. repeater) applications as well as

dual mode applications (i.e. 10/100 nodes or switches.)

If the DP83840A completes Auto-Negotiation as a result of

Parallel Detection, bits 5 and 7 within the ANLPAR register

(register address 05h) will be set to reﬂect the mode of

operation present in the Link Partner. Software may

determine that negotiation completed via Parallel Detection

by reading a zero in the Link Partner Auto-Negotiation Able

bit (bit 0, register address 06h) once the Auto-Negotiation

Complete bit (bit 5, register address 01h) is set. In the

event that more than one more than one PMA indicates a

valid link, the Multiple Link Fault bit (bit 4, register address

06h) will be set.

As an example of Parallel Detection, when the Link Partner

supports 100BASE-TX but does not support Auto-

Negotiation, Parallel Detection will allow the DP83840A to

negotiate to 100 Mb/s Half Duplex operation by detecting a

valid set of IDLEs even though no Link Code Words were

exchanged through FLP Bursts. A similar process on

connection to a Link Partner that supports 10BASE-T but

does not support Auto-Negotiation (i.e. the majority of

installed 10BASE-T connections), where the DP83840A

will negotiate to 10BASE-T Half Duplex operation by

detecting valid link pulses separated by 8-24 ms.

3.9.4 Auto-Negotiation Restart

Once Auto-Negotiation has completed it may be restarted

at any time by setting bit 9 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 DP83840A halt any

transmit

data

and

link

pulse

activity

until

the

break_link_timer expires (1500ms). Consequently, the Link

Partner will go into link fail and normal Auto-Negotiation

resumes. TheDP83840A will resume Auto-Negotiation

after the break_link_timer has expired by issuing FLP (fast

Link Pulse) bursts.

3.9.5 Enabling Auto-Negotiation via Software

It is important to note that if the DP83840A has been

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

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

negotiation of re-auto-negotiation be initiated via software,

bit 12 of the Basic Mode Control Register (address 00h)

must ﬁrst be cleared and then set for any auto-negotiation

function to take effect.

DP83840AVCE Datasheet(PDF) 39 Page - Texas Instruments

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