Datasheet

 2016 Microchip Technology Inc. DS00002164B-page 23
LAN8710A/LAN8710AI
On detection of one of these events, the transceiver begins auto-negotiation by transmitting bursts of Fast Link Pulses
(FLP), which are bursts of link pulses from the 10M transmitter. They are shaped as Normal Link Pulses and can pass
uncorrupted down CAT-3 or CAT-5 cable. A Fast Link Pulse Burst consists of up to 33 pulses. The 17 odd-numbered
pulses, which are always present, frame the FLP burst. The 16 even-numbered pulses, which may be present or absent,
contain the data word being transmitted. Presence of a data pulse represents a “1”, while absence represents a “0”.
The data transmitted by an FLP burst is known as a “Link Code Word.” These are defined fully in IEEE 802.3 clause 28.
In summary, the transceiver advertises 802.3 compliance in its selector field (the first 5 bits of the Link Code Word). It
advertises its technology ability according to the bits set in the
Auto Negotiation Advertisement Register.
There are 4 possible matches of the technology abilities. In the order of priority these are:
• 100M Full Duplex (Highest Priority)
• 100M Half Duplex
• 10M Full Duplex
• 10M Half Duplex (Lowest Priority)
If the full capabilities of the transceiver are advertised (100M, Full Duplex), and if the link partner is capable of 10M and
100M, then auto-negotiation selects 100M as the highest performance mode. If the link partner is capable of half and
full duplex modes, then auto-negotiation selects full duplex as the highest performance operation.
Once a capability match has been determined, the link code words are repeated with the acknowledge bit set. Any dif-
ference in the main content of the link code words at this time will cause auto-negotiation to re-start. Auto-negotiation
will also re-start if not all of the required FLP bursts are received.
The capabilities advertised during auto-negotiation by the transceiver are initially determined by the logic levels latched
on the MODE[2:0] configuration straps after reset completes. These configuration straps can also be used to disable
auto-negotiation on power-up. Refer to
Section 3.7.2, "MODE[2:0]: Mode Configuration," on page 30 for additional infor-
mation.
Writing the bits 8 through 5 of the Auto Negotiation Advertisement Register allows software control of the capabilities
advertised by the transceiver. 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.
Note: The device does not support “Next Page” capability.
3.2.1 PARALLEL DETECTION
If the LAN8710A/LAN8710Ai is connected to a device lacking the ability to auto-negotiate (for example, 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 interoperability with legacy link partners. If a link is formed via parallel detection, then the
Link Part-
ner Auto-Negotiation Able bit of the Auto Negotiation Expansion Register is cleared to indicate that the Link Partner is
not capable of auto-negotiation. The controller has access to this information via the management interface. If a fault
occurs during parallel detection, the
Parallel Detection Fault bit of Link Partner Auto-Negotiation Able is set.
Auto Negotiation Link Partner Ability Register 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 the Auto Negotiation Link Partner Ability Register
is updated after completion of parallel detection to reflect the speed capability of the link partner.
3.2.2 RESTARTING AUTO-NEGOTIATION
Auto-negotiation can be restarted at any time by setting the Restart Auto-Negotiate bit of the Basic Control Register.
Auto-negotiation will also restart 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 setting the Restart Auto-Negotiate bit of the Basic Control Reg-
ister, the LAN8710A/LAN8710Ai will respond by stopping all transmission/receiving operations. Once the break_link_-
timer is completed in the Auto-negotiation state-machine (approximately 1200ms), 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-negoti
-
ation.