LAN9500 Datasheet, PDF (76/213 Pages) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

LAN950x
5.6.6.2 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.
5.6.6.3 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 5-56 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 5.4.2.6, "TX Status
Format," on page 50). The CRS value, and subsequently the No Carrier value, are invalid during any full-duplex trans-
mission. Therefore, these signals cannot be used as a verification method of transmitted packets when transmitting in
10/100 Mbps full-duplex modes.
TABLE 5-56: CRS BEHAVIOR
Mode
Manual
Manual
Manual
Manual
Manual
Manual
Manual
Manual
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Auto-Negotiation
Speed
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 5-1)
Active
Active
Low
Active
Active
Active
Low
Active
Active
Active
Low
Active
Active
Active
Low
Active
Note 5-1
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.
5.6.7 HP AUTO-MDIX
HP Auto-MDIX facilitates the use of CAT-3 (10 BASE-T) or CAT-5 (100 BASE-T) media UTP interconnect cable without
consideration of interface wiring scheme. If a user plugs in either a direct connect LAN cable, or a cross-over patch
cable, as shown in Figure 5-19, the device’s Auto-MDIX PHY is capable of configuring the TPO and TPI twisted pair
pins for correct transceiver operation.
The internal logic of the device detects the TX and RX pins of the connecting device. Since the RX and TX line pairs
are interchangeable, special PCB design considerations are needed to accommodate the symmetrical magnetics and
termination of an Auto-MDIX design.
DS00001875A-page 76
 2010 - 2015 Microchip Technology Inc.