LAN9730 Datasheet, PDF (83/222 Pages) SMSC Corporation – High-Speed Inter-Chip (HSIC) USB 2.0

LAN9730/LAN9730i
4.6.6.3 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 internal 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, the internal CRS
responds only to receive activity. The CSMA/CD protocol does not apply and collision detection is disabled.
Table 4-55 describes the behavior of the internal CRS bit under all receive/transmit conditions.
The internal CRS signal is used to trigger bit 10 (No Carrier) of the TX Status Word (see Section 4.4.2.6, "TX Status
Format"). The CRS value, and subsequently the No Carrier value, are invalid during any full-duplex transmission. There-
fore, these signals cannot be used as a verification method of transmitted packets when transmitting in 10/100 Mbps
full-duplex modes.
TABLE 4-55: CRS BEHAVIOR
Mode
Speed
Duplex
Activity
CRS Behavior
Note 4-25
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
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
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Transmitting
Receiving
Active
Active
Low
Active
Active
Active
Low
Active
Active
Active
Low
Active
Active
Active
Low
Active
Note 4-25
The device’s 10/100 PHY internal CRS signal operates in two modes: Active and Low. When in Active
mode, the internal CRS will transition high and low upon line activity, where a high value indicates a
carrier has been detected. In Low mode, the internal CRS stays low and does not indicate carrier
detection. The internal CRS signal and No Carrier (bit 10 of the TX Status Word) cannot be used as
a verification method of transmitted packets when transmitting in 10/100 Mbps full-duplex mode.
 2012-2015 Microchip Technology Inc.
DS00001946A-page 83