LAN8810 Datasheet, PDF (29/83 Pages) Microchip Technology – GMII 10/100/1000 Ethernet Transceiver

LAN8810/LAN8810I
3.9.6 LINK INTEGRITY
This section details the establishment, maintenance and removal of links between the device and a link partner in
1000BASE-T, 100BASE-TX and 10BASE-T modes. Link status is reported in the Link Status bit of the Basic Status Reg-
ister. The link status is also used to drive the device LEDs as described in Section 3.9.1, "LEDs," on page 27.
3.9.6.1 Establishing and Maintaining a Link
Once a link state is determined via auto-negotiation, parallel detection, or forced operation, the device and the link part-
ner establish a link.
The completion of the auto-negotiation process is reported via the Auto-Negotiate Complete bit of the Basic Status Reg-
ister and issues an interrupt as described in Section 3.5, "Interrupt Management," on page 21. The speed of the link is
reported in the Speed Indication field of the PHY Special Control / Status Register. The speed is also reported on the
LED pins for any link.
Failure to complete the auto-negotiation process is reported through the following status bits:
• Parallel Detection Fault reported in the Auto Negotiation Expansion Register while operating in 10BASE-T or
100BASE-TX modes.
• Master/Slave Configuration Fault reported in the Master/Slave Status Register while operating in 1000BASE-T
mode.
A fault occurs if the Master/Slave configuration conditions do not allow master/slave resolution, as defined in the Master/
Slave Manual Config Enable and Master/Slave Manual Config Value bits in the Master/Slave Control Register of the
local and remote link partners.
3.9.6.2 1000BASE-T
For 1000BASE-T links, the device and its link partner enter a training phase after completion of the auto-negotiation
process. The links exchange idle symbols and use the information obtained from receiving this signal to set their adap-
tive filter coefficients.
These coefficients are used in the receiver to equalize the incoming signal, as well as eliminate signal impairments such
as echo and cross-talk. Each side indicates completion of the training phase to its link partner by changing the encoding
of the idle-symbols it transmits.
The link is established after both sides indicate completion of the training phase. Each side continues to send idle sym-
bols whenever it has no data to transmit. The link is maintained as long as valid idle, data, or carrier extension symbols
are received.
Status of both local and remote receivers is reported in the Local Receiver Status and Remote Receiver Status bits of
the Master/Slave Status Register.
The device also provides an advanced Auto Link Breaker feature (only for 1000BASE-T links). Using this feature, the
link can be taken down if the bit error rate (BER) exceeds the threshold defined in Link Break Threshold field of the Link
Control Register. The error counting occurs during the idle time for a period commensurate with the specified BER. The
Auto Link Breaker feature is enabled via the Link Break Enable bit of the Link Control Register.
3.9.6.3 100BASE-TX
For 100BASE-TX links, the device and its link partner begin transmitting idle symbols after completion of the auto-nego-
tiation process. Each side continues sending idle symbols whenever it has no data to transmit. The link is maintained
as long as valid idle symbols or data are received.
3.9.6.4 10BASE-T
For 10BASE-T links, the device and its link partner begin exchanging normal link pulses (NLPs) after completion of the
auto-negotiation process. The device transmits an NLP every 16ms and expects to receive an NLP every 8 to 24ms. A
link is maintained as long as NLPs are received.
3.9.6.5 Taking Down a Link
The device takes down an established link when the required conditions are no longer met. When a link is down, data
transmission stops. For 10BASE-T links, the link is taken down after NLPs are no longer received. For 100BASE-TX
and 1000BASE-T links, the link is taken down after valid idle codes are no longer received.
After a link is down, the device does the following:
• If auto-negotiation is enabled, the device re-enters the auto-negotiation phase and begins transmitting FLPs
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DS00001870B-page 29