DP83867CS datasheet(32/129 Pages) TI2

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7.4.3.3 Pause and Asymmetrical Pause Resolution

When Full-Duplex operation is selected during priority resolution, the Auto-Negotiation also determines the Flow

Control capabilities of the two link partners. Flow control was originally introduced to force a busy station’s Link

Partner to stop transmitting data in Full-Duplex operation. Unlike Half-Duplex mode of operation where a link

partner can be forced to back off by simply generating collisions, the Full-Duplex operation needed a mechanism

to slow down transmission from a link partner in the event that the receiving station’s buffers are becoming

full. A new MAC control layer was added to handle the generation and reception of Pause Frames. Each MAC

Controller has to advertise whether the controller is capable of processing Pause Frames. In addition, the MAC

Controller advertises if Pause frames can be handled in both directions, that is, receive and transmit. If the MAC

Controller only generates Pause frames but does not respond to Pause frames generated by a link partner,

the event is called Asymmetrical Pause. The advertisement of Pause and Asymmetrical Pause capabilities is

enabled by writing 1 to bits 10 and 11 of ANAR (register address 0x0004). The link partner’s Pause capabilities

is stored in ANLPAR (register address 0x0005) bits 10 and 11. The MAC Controller has to read from ANLPAR

to determine which Pause mode to operate. The PHY layer is not involved in Pause resolution other than simply

advertising and reporting of Pause capabilities.

7.4.3.4 Next Page Support

The DP83867 supports the Auto-Negotiation Next Page protocol as required by IEEE 802.3 clause 28.2.4.1.7.

The ANNPTR 0x07 allows for the configuration and transmission of the Next Page. Refer to clause 28 of the

IEEE 802.3 standard for detailed information regarding the Auto-Negotiation Next Page function.

7.4.3.5 Parallel Detection

The DP83867 supports the Parallel Detection function as defined in the IEEE 802.3 specification. Parallel

Detection requires the 10/100Mbps 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 10BASE-Te or

100BASE-X PMA recognize as valid link signals.

If the DP83867 completes Auto-Negotiation as a result of Parallel Detection, without Next Page operation, bits 5

and 7 of ANLPAR (register address 0x0005) are set to reflect the mode of operation present in the Link Partner.

Note that bits 4:0 of the ANLPAR are also set to 00001 based on a successful parallel detection to indicate a

valid 802.3 selector field. Software can determine that the negotiation is completed through Parallel Detection

by reading 0 in bit 0 of ANER (register address 0x006) after Auto-Negotiation Complete, bit 5 of BMSR (register

address 0x0001), is set. If the PHY is configured for parallel detect mode and any condition other than a good

link occurs, the parallel detect fault, bit 4 of ANER (register address 0x06), sets.

7.4.3.6 Restart Auto-Negotiation

If a link is established by successful Auto-Negotiation and then lost, the Auto-Negotiation process resumes to

determine the configuration for the link. This function confirms that a link can be re-established if the cable

becomes disconnected and reconnected. After Auto-Negotiation is completed, the process can be restarted

at any time by writing 1 to bit 9 of the BMCR (register address 0x0000). A restart Auto-Negotiation request

from any entity, such as a management agent, causes DP83867 to halt data transmission or link pulse activity

until the break_link_timer expires. Consequently, the Link Partner goes into link fail mode and the resume

Auto-Negotiation. The DP83867 resumes Auto-Negotiation after the break_link_timer has expired by transmitting

FLP (Fast Link Pulse) bursts.

7.4.3.7 Enabling Auto-Negotiation Through Software

If Auto-Negotiation is disabled by MDIO access, and the user desires to restart Auto-Negotiation, this can be

accomplished by software access. Bit 12 of BMCR (register address 0x00) can be cleared and then set for

Auto-Negotiation operation to take place.

If Auto-Negotiation is disabled by strap option, Auto-Negotiation can not be reenabled.

DP83867CS, DP83867IS, DP83867E

SNLS504F – OCTOBER 2015 – REVISED JANUARY 2025

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