lan9420 Standard Microsystems Corp., lan9420 Datasheet - Page 72

• Manufacturer Part Number: lan9420
• Description: Lan9420/lan9420i Single-chip Ethernet Controller With Hp Auto-mdix Support And Pci Interface
• Manufacturer: Standard Microsystems Corp.

Revision 1.1 (03-31-08)
3.6.6.2
3.6.6.3
3.6.7
3.6.8
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 carrier sense signal, CRS, responds
to both transmit and receive activity.
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.
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
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.
PHY Power-Down Modes
There are 2 power-down modes for the PHY as discussed in the following sections.
Not Used
Not Used
Not Used
Not Used
TPO+
TPO-
Figure 3.27 Direct Cable Connection vs. Cross-Over Cable Connection
TPI+
TPI-
RJ-45 8-pin straight-through
1
2
3
4
5
6
7
8
for 10BASE-T/100BASE-TX
Direct Connect Cable
signaling
1
2
3
4
5
6
7
8
TPO+
TPO-
TPI+
Not Used
Not Used
TPI-
Not Used
Not Used
Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
DATASHEET
In this mode, If data is received while the PHY is transmitting,
72
Not Used
Not Used
Not Used
Not Used
TPO+
TPO-
TPI+
TPI-
1
2
3
4
5
6
7
8
RJ-45 8-pin cross-over for
10BASE-T/100BASE-TX
Cross-Over Cable
signaling
Figure 3.27 on page
1
2
3
4
5
6
7
8
TPO+
TPO-
TPI+
Not Used
Not Used
TPI-
Not Used
Not Used
SMSC LAN9420/LAN9420i
Datasheet
72, the