Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface

Datasheet

3.6.6.3Half 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 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.

3.6.7HP 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 3.27 on page 72, the LAN9420/LAN9420i Auto-MDIX PHY is capable of configuring the TPO+/TPO- and TPI+/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.

The Auto-MDIX function can be disabled through an internal register 27.15, or the external AUTOMDIX_EN configuration strap. When Auto-MDIX mode is disabled (27.15 = 1), the TX and RX pins can be configured as desired using the MDIX State (27.13) control bit.

 

RJ-45 8-pin straight-through

 

 

 

RJ-45 8-pin cross-over for

 

 

for 10BASE-T/100BASE-TX

 

 

 

 

10BASE-T/100BASE-TX

 

 

 

 

signaling

 

 

 

 

 

signaling

 

TPO+

1

 

 

1

TPO+

 

TPO+

1

 

 

1

TPO+

 

 

 

TPO-

2

 

 

2

TPO-

 

TPO-

2

 

 

2

TPO-

 

 

 

TPI+

3

 

 

3

TPI+

 

TPI+

3

 

 

3

TPI+

 

 

 

Not Used

4

 

 

4

Not Used

 

Not Used

4

 

 

4

Not Used

Not Used

5

 

 

5

Not Used

 

Not Used

5

 

 

5

Not Used

TPI-

6

 

 

6

TPI-

 

TPI-

6

 

 

6

TPI-

 

 

 

Not Used

7

 

 

7

Not Used

 

Not Used

7

 

 

7

Not Used

Not Used

8

 

 

8

Not Used

 

Not Used

8

 

 

8

Not Used

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Direct Connect Cable

 

 

 

 

 

Cross-Over Cable

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3.27 Direct Cable Connection vs. Cross-Over Cable Connection

3.6.8PHY Power-Down Modes

There are 2 power-down modes for the PHY as discussed in the following sections.

3.6.8.1General Power-Down

This power-down is controlled by register 0, bit 11. In this mode the PHY, except the management interface, is powered-down and stays in that condition as long as PHY register bit 0.11 is HIGH. When bit 0.11 is cleared, the PHY powers up and is automatically reset. Please refer to Section 4.5.1, "Basic Control Register," on page 136 for additional information on this register.

Revision 1.22 (09-25-08)

72

SMSC LAN9420/LAN9420i

 

DATASHEET