SMSC LAN9311 User Manual

Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface

Revision 1.4 (08-19-08)

92

SMSC LAN9311/LAN9311i

 

The Port 1 & 2 PHYs are capable of generating and receiving pause flow control frames per the IEEE
802.3 specification. The PHYs advertised pause flow control abilities are set via bits 10 (Symmetric
Pause) and 11 (Asymmetric Pause) of the 

. This allows the PHY to advertise its flow control abilities and auto-negotiate the

flow control settings with its link partner. The default values of these bits are determined via
configuration straps as defined in 

.

The pause flow control settings may also be manually set via the manual flow control registers 

 and 

. These registers allow the switch fabric ports flow control settings to be manually set

when auto-negotiation is disabled or the Manual Flow Control Select bit 0 is set. The currently enabled
duplex and flow control settings can also be monitored via these registers. The flow control values in
the 

 are not affected by the

values of the manual flow control register. Refer to 

 for additional information.

If the LAN9311/LAN9311i 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 802.3
standard. This ability is known as “Parallel Detection.” This feature ensures interoperability with legacy
link partners. If a link is formed via parallel detection, then bit 0 in the 

 is cleared to indicate that the link partner is not capable of auto-

negotiation. If a fault occurs during parallel detection, bit 4 of the 

 is set.

T h e  

 is used to store the Link Partner Ability information, which is coded

in the received FLPs. If the link partner is not auto-negotiation capable, then this register is updated
after completion of parallel detection to reflect the speed capability of the link partner.

Auto-negotiation can be re-started at any time by setting bit 9 of the 

. 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 

, the LAN9311/LAN9311i will respond by stopping all

transmission/receiving operations. Once the internal break link time of approximately 1200ms has
passed in the Auto-negotiation state-machine, the auto-negotiation will re-start. In this case, the link
partner will have also dropped the link due to lack of a received signal, so it too will resume auto-
negotiation.

Auto-negotiation can be disabled by clearing bit 12 of the 

. The PHY will then force its speed of operation to reflect the speed (bit

13) and duplex (bit 8) of the 

. The

speed and duplex bits in the 

be ignored when auto-negotiation is enabled.