LAN83C185_03 Datasheet, PDF (27/65 Pages) SMSC Corporation – High Performance Single Chip Low Power 10/100 Ethernet Physical Layer Transceiver

High Performance Single Chip Low Power 10/100 Ethernet Physical Layer Transceiver (PHY)
Datasheet
■ 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 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 PHY 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 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 difference 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 PHY are initially determined by the logic
levels latched on the MODE[2:0] bus after reset completes. This bus can also be used to disable auto-
negotiation on power-up.
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 LAN83C185 does not support “Next Page" capability.
4.7.1 Parallel Detection
If the LAN83C185 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 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 controller 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 capability of the Link Partner.
SMSC LAN83C185
19
DATASHEET
Rev. 0.6 (12-12-03)