LAN8810 Datasheet, PDF (14/83 Pages) Microchip Technology – GMII 10/100/1000 Ethernet Transceiver

LAN8810/LAN8810I
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 Reg-
ister is cleared to indicate that the Link Partner is not capable of auto-negotiation. If a fault occurs during parallel detec-
tion, 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 26 or by using the Master/Slave Manual Config Enable and Master/
Slave Manual Config Value bits of the Master/Slave Control Register. If both the link partner and the local device are
manually given the same Master/Slave assignment, an error will be indicated in the Master/Slave Configuration Fault
bit of the Master/Slave Status Register.
Depending on the link partner configuration, the manual Master/Slave mode can be resolved to sixteen possible out-
comes, as shown in Table 3-1.
TABLE 3-1: MASTER/SLAVE RESOLUTION FOR 1000BASE-T
LAN8810/LAN8810i
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Link Partner
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Single-Port
Single-Port
Single-Port
Multi-Port
Single-Port
Manual Master
Single-Port
Manual Slave
Multi-Port
Single-Port
Multi-Port
Multi-Port
Multi-Port
Manual Master
Multi-Port
Manual Slave
Manual Master
Single-Port
LAN8810/LAN8810i Result
M/S resolved by random seed
Slave
Slave
Master
Master
M/S resolved by random seed
Slave
Master
Master
Link Partner Result
M/S resolved by random seed
Master
Master
Slave
Slave
M/S resolved by random seed
Master
Slave
Slave
DS00001870B-page 14
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