LAN9500 Datasheet, PDF (75/213 Pages) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

LAN950x
When enabled, auto-negotiation is started by the occurrence of one of the following events:
• Hardware reset
• Software reset
• Power-down reset
• Link status down
• Setting register 0, bit 9 high (auto-negotiation restart)
On detection of one of these events, the PHY begins auto-negotiation by transmitting bursts of Fast Link Pulses (FLP).
These are bursts of link pulses from the 10M transmitter. They are shaped as Normal Link Pulses and can pass uncor-
rupted 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 PHY advertises 802.3 compliance in its selector field (the first 5 bits of the Link Code Word). It adver-
tises its technology ability according to the bits set in register 4 of the SMI registers.
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
If the full capabilities of the PHY 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.
Writing register 4 bits [8:5] allows software control of the capabilities advertised by the PHY. Writing register 4 does not
automatically re-start auto-negotiation. Register 0, bit 9 must be set before the new abilities will be advertised. Auto-
negotiation can also be disabled via software by clearing register 0, bit 12.
The device does not support “Next Page” capability.
5.6.6 PARALLEL DETECTION
If LAN950x is connected to a device lacking the ability to auto-negotiate (i.e. no FLPs are detected), it is able to deter-
mine 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 bit 0 in register 6 is cleared to
indicate that the Link Partner is not capable of auto-negotiation. The Ethernet MAC has access to this information via
the management interface. If a fault occurs during parallel detection, bit 4 of register 6 is set.
Register 5 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 register 5 is updated after completion of parallel detection to reflect the speed capa-
bility of the Link Partner.
5.6.6.1 Re-starting Auto-negotiation
Auto-negotiation can be re-started at any time by setting register 0, bit 9. 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 control register, the device will respond by
stopping all transmission/receiving operations. Once the break_link_timer is done, in the Auto-negotiation state-
machine (approximately 1200 mS) the auto-negotiation will re-start. The Link Partner will have also dropped the link due
to lack of a received signal, so it too will resume auto-negotiation.
 2010 - 2015 Microchip Technology Inc.
DS00001875A-page 75