LAN9211 datasheet(74/146 Pages) SMSC

74 / 146 page

High-Performance Small Form Factor Single-Chip Ethernet Controller with HP Auto-MDIX

Datasheet

Revision 1.93 (11-27-07)

SMSC

LAN9211

DATASHEET

abilities will be advertised. Auto-negotiation can also be disabled via software by clearing register 0,

bit 12.

The LAN9211 does not support “Next Page" capability.

4.7

Parallel Detection

If the LAN9211 is connected to a device lacking the ability to auto-negotiate (i.e. no FLPs are

detected), it is able to determine the speed of the link based on either 100M MLT-3 symbols or 10M

Normal Link Pulses. In this case the link is presumed to be half-duplex per the IEEE standard. This

ability is known as “Parallel Detection. This feature ensures inter operability with legacy link partners.

If a link is formed via parallel detection, then bit 0 in register 6 is cleared to indicate that the Link

Partner is not capable of auto-negotiation. The Ethernet MAC has access to this information via the

management interface. If a fault occurs during parallel detection, bit 4 of register 6 is set.

If the Link Partner is not auto-negotiation capable, then register 5 is updated after completion of parallel

detection to reflect the speed capability of the Link Partner.

4.7.1

Re-starting Auto-negotiation

Auto-negotiation can be re-started at any time by setting register 0, bit 9. Auto-negotiation will also re-

start if the link is broken at any time. A broken link is caused by signal loss. This may occur because

of a cable break, or because of an interruption in the signal transmitted by the Link Partner. Auto-

negotiation resumes in an attempt to determine the new link configuration.

If the management entity re-starts Auto-negotiation by writing to bit 9 of the control register, the

LAN9211 will respond by stopping all transmission/receiving operations. Once the break_link_timer is

done, in the Auto-negotiation state-machine (approximately 1200ms) the auto-negotiation will re-start.

The Link Partner will have also dropped the link due to lack of a received signal, so it too will resume

auto-negotiation.

4.7.2

Disabling Auto-negotiation

Auto-negotiation can be disabled by setting register 0, bit 12 to zero. The device will then force its

speed of operation to reflect the information in register 0, bit 13 (speed) and register 0, bit 8 (duplex).

The speed and duplex bits in register 0 should be ignored when auto-negotiation is enabled.

4.7.3

Half vs. Full-Duplex

Half-duplex operation relies on the CSMA/CD (Carrier Sense Multiple Access / Collision Detect)

protocol to handle network traffic and collisions. In this mode, the internal carrier sense signal, CRS,

responds to both transmit and receive activity.

In this mode, If data is received while the PHY is

transmitting, a collision results.

In full-duplex mode, the PHY is able to transmit and receive data simultaneously. In this mode, the

internal CRS responds only to receive activity. The CSMA/CD protocol does not apply and collision

detection is disabled.

Table 4.2 describes the behavior of the internal CRS bit under all receive/transmit conditions. The

internal CRS signal is used to trigger bit 10 (No Carrier) of the TX Status word (See Section 3.12.4,

"TX Status Format"). The CRS value, and subsequently the No Carrier value, are invalid during any

full-duplex transmission. Therefore, these signals cannot be used as a verification method of

transmitted packets when transmitting in 10/100 Mbps full-duplex modes.

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