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If both the link partner and the local device are manually

given the same MASTER/SLAVE assignment, then an

error condition will exist as indicated by bit 15 of register

0x0A. If one of the link partners is manually assigned a

Master/Slave status while the other is not, then the manual

assignment will take higher priority during the resolution

process.

When Manual Slave or Manual Master mode is enabled

Auto-Negotiation should also be enabled as per the 802.3

IEEE specification. The DP83861, however will link up to

another DP83861 when Auto-Negotiation is disabled and

one DP83861 is manually configured as a Master and the

other is manually configured as a Slave.

An alternative way of specifying Master or Slave mode is to

use the Port_Type strapping option pin 208 or by writing to

written to bit 10 the part will advertise that it wants to be a

Master. When pin 208 is pulled low or a 0 is written to bit 10

the part will advertise that it wants to be a Slave. If two

devices advertise that they want to both be Master or both

to be Slaves then the Auto-Negotiation statemachine will

go through a random number arbitration sequence to pick

which one will be the Master and which one will be the

Slave. Using this method will eliminate the chance of an

unresolved link.

2.3 Auto-Negotiation

All 1000BASE-T PHYs are required to support Auto-Nego-

tiation. The Auto-Negotiation function in 1000BASE-T has

four primary purposes:

— Auto-Negotiation Priority Resolution

— Auto-Negotiation MASTER/SLAVE Resolution

— Auto-Negotiation PAUSE/ ASYMMETRICAL PAUSE

Resolution

— Auto-MDIX resolution

2.3.1 Auto-Negotiation Priority Resolution

First the Auto-Negotiation function provides a mechanism

for exchanging configuration information between two ends

of a link segment and automatically selecting the highest

performance mode of operation supported by both devices.

Fast Link Pulse (FLP) Bursts provide the signalling used to

communicate

Auto-Negotiation

abilities

between

two

devices at each end of a link segment. For further details

regarding Auto-Negotiation, refer to Clause 28 of the IEEE

802.3u specification. The DP83861 supports six different

Ethernet protocols: 10BASE-T Full Duplex, 10BASE-T Half

Duplex, 100BASE-TX Full Duplex, 100BASE-TX Half

Duplex, 1000BASE-T Full Duplex and 1000BASE-T Half

Duplex, so the inclusion of Auto-Negotiation ensures that

the highest performance protocol will be selected based on

the advertised ability of the Link Partner.

Auto-Negotiation Priority Resolution for the DP83861:

1. 1000BASE-T Full Duplex (Highest Priority)

2. 1000BASE-T Half Duplex

3. 100BASE-TX Full Duplex

4. 100BASE-TX Half Duplex

5. 10BASE-T Full Duplex

6. 10BASE-T Half Duplex (Lowest Priority)

2.3.2 Auto-Negotiation MASTER/SLAVE Resolution

The second goal of Auto-Negotiation in 1000BASE-T

devices is to resolve MASTER/SLAVE configuration. If both

devices have disabled manual Master/Slave configuration,

MASTER priority is given to the devices which support mul-

tiport nodes (i.e. Switches and Repeaters take higher

priority over DTEs or single node systems.).

SPEED[0]/PORT_TYPE is a strap option for advertising

the Multi-node functionality. (See Table 4) If both PHYs

advertise the same options then the Master/Slave resolu-

tion is resolved by a random number generation. See IEEE

802.3ab Clause 40.5.1.2 and Table 3 for more details.

2.3.3 Auto-Negotiation PAUSE and Asymmetrical

PAUSE Resolution

Auto-Negotiation is also used to determine the Flow Con-

trol capabilities of the two link partners. Flow control was

originally introduced as a mechanism to force a busy sta-

tion’s Link Partner to stop sending data when in Full Duplex

mode of operation. Unlike Half Duplex mode of operation

where a link partner could be forced to back off by simply

causing collisions, the Full Duplex operation needed a for-

mal mechanism to slow down a link partner in the event of

the receiving station’s buffers becoming full. A new MAC

control layer was added to handle the generation and

reception of Pause Frames which contained a timer indi-

cating the amount of Pause requested. Each MAC/Control-

ler has to advertise whether it can handle PAUSE frames,

and whether they support PAUSE frames in both direc-

tions. (i.e. receive and transmit. If the MAC/Controller will

only generate PAUSE frames but will not respond to

PAUSE frames generated by a link partner, then this is

called Asymmetrical PAUSE.) Advertisement of these

capabilities can be achieved by writing a ‘1’ to bits 10 and

11 of the Auto-Neg Advertisement register (Address 0x04).

The link partners PAUSE capabilities can be determined

from register 0x05 using these same bits. The MAC/con-

troller has to write to and read from these registers and

determine which mode of PAUSE operation to choose. The

PHY layer is not involved in Pause resolution other than

the simple advertising and reporting of PAUSE capabilities.

These capabilities are MAC specific. The MAC conveys

these capabilities by writing to the appropriate PHY regis-

ters.

2.3.4 Auto-Negotiation Auto-MDIX Resolution

The DP83861 can determine if a “straight” or “cross-over”

cable is being used to connect to the link partner and can

automatically re-assign channel A and channel B to estab-

lish link with the link partner. Although not part of the Auto-

Negotiation FLP exchange process, the Auto-MDIX resolu-

tion requires that Auto-Negotiation is enabled. Auto-MDIX

resolution will precede the actual Auto-Negotiation process

which involves exchange of FLPs to advertise capabilities.

If Auto-Negotiation is not enabled, then the MDIX function

can be manually configured by disabling Auto-MDIX. See

Section 8.16 on FAQs for details.

2.3.5 Auto-Negotiation Strap Option Control

The Auto-Negotiation function within the DP83861 can be

controlled either by internal register access or by the use of

the AN_EN, and various strap pin values during power-

on/reset. Table 4 shows how the various strap pin values

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