LAN9353 Datasheet, PDF (103/523 Pages) Microchip Technology – Interfaces at up to 200Mbps via Turbo MII

LAN9353
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 mode.
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 the PHY x Auto-Negotiation Advertisement Register (PHY_AN_ADV_x) bits [8:5] allows software control of the
capabilities advertised by the transceiver. Writing the PHY x Auto-Negotiation Advertisement Register (PHY_AN_AD-
V_x) does not automatically re-start Auto-Negotiation. The Restart Auto-Negotiation (PHY_RST_AN) bit of the PHY x
Basic Control Register (PHY_BASIC_CONTROL_x) must be set before the new abilities will be advertised. Auto-Nego-
tiation can also be disabled via software by clearing the Auto-Negotiation Enable (PHY_AN) bit of the PHY x Basic Con-
trol Register (PHY_BASIC_CONTROL_x).
9.2.6.1 Pause Flow Control
The Switch Fabric MACs are capable of generating and receiving pause flow control frames per the IEEE 802.3 speci-
fication. The PHY’s advertised pause flow control abilities are set via the Asymmetric Pause and Symmetric Pause bits
of the PHY x Auto-Negotiation Advertisement Register (PHY_AN_ADV_x). This allows the PHY to advertise its flow con-
trol abilities and Auto-Negotiate the flow control settings with its link partner. The default values of these bits are deter-
mined via configuration straps as defined in Section 9.2.20.5, "PHY x Auto-Negotiation Advertisement Register
(PHY_AN_ADV_x)," on page 129.
9.2.6.2 Parallel Detection
If the device 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 802.3 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 Partner Auto-
Negotiation Able bit of the PHY x Auto-Negotiation Expansion Register (PHY_AN_EXP_x) is cleared to indicate that the
link partner is not capable of Auto-Negotiation. If a fault occurs during parallel detection, the Parallel Detection Fault bit
of the PHY x Auto-Negotiation Expansion Register (PHY_AN_EXP_x) is set.
The PHY x Auto-Negotiation Link Partner Base Page Ability Register (PHY_AN_LP_BASE_ABILITY_x) is used to store
the Link Partner Ability information, which is coded in the received FLPs. If the link partner is not Auto-Negotiation capa-
ble, then this register is updated after completion of parallel detection to reflect the speed capability of the link partner.
9.2.6.3 Restarting Auto-Negotiation
Auto-Negotiation can be re-started at any time by setting the Restart Auto-Negotiation (PHY_RST_AN) bit of the PHY
x Basic Control Register (PHY_BASIC_CONTROL_x). 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 setting the Restart Auto-Negotiation (PHY_RST_AN) bit of the
PHY x Basic Control Register (PHY_BASIC_CONTROL_x), the device will respond by stopping all transmission/receiv-
ing operations. Once the internal break_link_time 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-Negotiation.
Auto-Negotiation is also restarted after the EEPROM Loader updates the straps.
9.2.6.4 Disabling Auto-Negotiation
Auto-Negotiation can be disabled by clearing the Auto-Negotiation Enable (PHY_AN) bit of the PHY x Basic Control
Register (PHY_BASIC_CONTROL_x). The transceiver will then force its speed of operation to reflect the information in
the PHY x Basic Control Register (PHY_BASIC_CONTROL_x) (Speed Select LSB (PHY_SPEED_SEL_LSB) and
Duplex Mode (PHY_DUPLEX)). These bits are ignored when Auto-Negotiation is enabled.
9.2.6.5 Half Vs. Full-Duplex
Half-duplex operation relies on the CSMA/CD (Carrier Sense Multiple Access / Collision Detect) protocol to handle net-
work traffic and collisions. In this mode, the carrier sense signal, CRS, responds to both transmit and receive activity. If
data is received while the transceiver is transmitting, a collision results.
 2015 Microchip Technology Inc.
DS00001925A-page 103