LAN8810I-AKZE Datasheet, PDF (20/100 Pages) Microchip Technology – GMII 10/100/1000 Ethernet Transceiver with HP Auto-MDIX Support

GMII 10/100/1000 Ethernet Transceiver with HP Auto-MDIX Support
Datasheet
However, writing the Auto Negotiation Advertisement Register does not automatically re-start auto-
negotiation. The Restart Auto-Negotiate bit of the Basic Control Register must be set before the new
abilities will be advertised. Auto-negotiation can also be disabled via software by clearing the Auto-
Negotiation Enable bit of the Basic Control Register.
Auto-Negotiation also resolves the Master/Slave clocking relationship between two PHYs for a
1000BASE-T link. Refer to Section 3.1.4, "Master/Slave," on page 20 for additional information.
3.1.1 Restarting Auto-negotiation
Auto-negotiation can be restarted at any time by using the Restart Auto-Negotiate bit of the Basic
Control Register. 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 restarts Auto-negotiation by writing to the Restart Auto-Negotiate bit, the
device will respond by stopping all transmission/receiving operations. Auto-negotiation will restart after
approximately 1200 mS. The Link Partner will have also dropped the link and will resume auto-
negotiation.
3.1.2 Disabling Auto-negotiation
Auto-negotiation can be disabled via software by clearing the Auto-Negotiation Enable bit of the Basic
Control Register. The device will then force its speed of operation to reflect the information in the
Speed Select[1], Speed Select[0], and Duplex Mode bits of the Basic Control Register. These bits are
ignored when auto-negotiation is enabled.
3.1.3 Parallel Detection
If the LAN8810/LAN8810i 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.
The Ethernet MAC has access to information regarding parallel detect via the Auto Negotiation
Expansion Register. If a link is formed via parallel detection, the Link Partner Auto-Negotiation Able bit
of the Auto Negotiation Expansion Register is cleared to indicate that the Link Partner is not capable
of auto-negotiation. If a fault occurs during parallel detection, the Parallel Detection Fault bit of this
register is set.
The Auto Negotiation Link Partner Ability Register is updated with information from the link partner
which is coded in the received FLPs. If the Link Partner is not auto-negotiation capable, then the Auto
Negotiation Link Partner Ability Register is updated after completion of parallel detection to reflect the
speed capability of the Link Partner.
Parallel detect cannot be used to establish Gigabit Ethernet links because echo cancellation and signal
recovery on a Gigabit Ethernet link requires resolution of the Master/Slave clock relationship, which
requires the exchange of FLPs.
3.1.4 Master/Slave
In 1000BASE-T, one of the two link partner devices must be configured as Master and the other as
Slave. The Master device transmits data using the local clock, while the Slave device uses the clock
recovered from incoming data.
The Master and Slave assignments are set using the configuration pins as described in Section
3.8.1.2.2, "Configuring the Mode of Operation (CONFIG[3:2])," on page 31 or by using the
Master/Slave Manual Config Enable and Master/Slave Manual Config Value bits of the Master/Slave
Revision 1.0 (02-06-13)
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DATASHEET
SMSC LAN8810/LAN8810i