LAN9117 Datasheet, PDF (57/114 Pages) SMSC Corporation – HIGH PERFORMANCE SINGLE-CHIP 10/100 NON-PCI ETHERNET CONTROLLER

LAN9117
4.7.1 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 LAN9117 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.
4.7.2 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.
4.7.3 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. In
this mode, If data is received while the PHY is transmitting, a collision results.
In full-duplex mode, the PHY is able to transmit and receive data simultaneously. In this mode, CRS responds only to
receive activity. The CSMA/CD protocol does not apply and collision detection is disabled. Table 4-2 describes the
behavior of the CRS bit under all receive/transmit conditions.
TABLE 4-2: CRS BEHAVIOR
Mode
Speed
Manual
Manual
Manual
Manual
Manual
Manual
Manual
Manual
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
10 Mbps
10 Mbps
10 Mbps
10 Mbps
100 Mbps
100 Mbps
100 Mbps
100 Mbps
10 Mbps
10 Mbps
10 Mbps
10 Mbps
100 Mbps
100 Mbps
100 Mbps
100 Mbps
Duplex
Half-Duplex
Half-Duplex
Full-Duplex
Full-Duplex
Half-Duplex
Half-Duplex
Full-Duplex
Full-Duplex
Half-Duplex
Half-Duplex
Full-Duplex
Full-Duplex
Half-Duplex
Half-Duplex
Full-Duplex
Full-Duplex
Activity
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
CRS Behavior
(Note 4-1)
Active
Active
Low
Active
Active
Active
Low
Active
Active
Active
Low
Active
Active
Active
Low
Active
Note 4-1
The LAN9117 10/100 PHY CRS signal operates in two modes: Active and Low. When in Active mode,
CRS will transition high and low upon line activity, where a high value indicates a carrier has been
detected. In Low mode, CRS stays low and does not indicate carrier detection. The CRS signal
cannot be used as a verification method of transmitted packets when transmitting in 10 or 100 Mbps
in full-duplex mode.
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DS00002267A-page 57