lan9217 Standard Microsystems Corp., lan9217 Datasheet - Page 67

• Manufacturer Part Number: lan9217
• Description: Lan9217 16-bit High-performance Single-chip 10/100 Ethernet Controller With Hp Auto-mdix Support
• Manufacturer: Standard Microsystems Corp.

16-bit High-Performance Single-Chip 10/100 Ethernet Controller with HP Auto-MDIX Support
Datasheet
SMSC LAN9217
4.7
4.7.1
4.7.2
4.7.3
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 LAN9217 does not support “Next Page" capability.
If the LAN9217 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 inter operability 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 capability of the Link Partner.
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
LAN9217 will respond by stopping all transmission/receiving operations. Once the break_link_timer is
done, in the Auto-negotiation state-machine (approximately 1200ms) 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.
Disabling Auto-negotiation
Auto-negotiation can be disabled by setting register 0, bit 12 to zero. The device will then force its
speed of operation to reflect the information in register 0, bit 13 (speed) and register 0, bit 8 (duplex).
The speed and duplex bits in register 0 should be ignored when auto-negotiation is enabled.
Half vs. Full-Duplex
Half-duplex operation relies on the CSMA/CD (Carrier Sense Multiple Access / Collision Detect)
protocol to handle network traffic and collisions. In this mode, the internal carrier sense signal, CRS,
responds to both transmit and receive activity.
transmitting, a collision results.
In full-duplex mode, the PHY is able to transmit and receive data simultaneously. In this mode, the
internal CRS responds only to receive activity. The CSMA/CD protocol does not apply and collision
detection is disabled.
Table 4.2
internal CRS signal is used to trigger bit 10 (No Carrier) of the TX Status word (See
"TX Status
full-duplex transmission. Therefore, these signals cannot be used as a verification method of
transmitted packets when transmitting in 10/100 Mbps full-duplex modes.
Parallel Detection
describes the behavior of the internal CRS bit under all receive/transmit conditions. The
Format"). The CRS value, and subsequently the No Carrier value, are invalid during any
DATASHEET
67
In this mode, If data is received while the PHY is
Revision 2.3 (08-06-08)
Section 3.12.4,