LAN9730 Datasheet, PDF (84/222 Pages) SMSC Corporation – High-Speed Inter-Chip (HSIC) USB 2.0

LAN9730/LAN9730i
4.6.7 HP AUTO-MDIX
HP Auto-MDIX facilitates the use of CAT-3 (10BASE-T) or CAT-5 (100BASE-TX) 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 4-19, 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.
The Auto-MDIX function can be disabled through the Special Control/Status Indications Register or the external
AUTOMDIX_EN configuration strap.
Note:
When operating in 10BASE-T or 100BASE-TX manual modes, the Auto-MDIX crossover time can be
extended via the Extend Manual 10/100 Auto-MDIX Crossover Time bit of the EDPD NLP/Crossover Tim-
eRegister. Refer to Section 6.5.8, "EDPD NLP/Crossover TimeRegister" for additional information.
FIGURE 4-19:
DIRECT CABLE CONNECTION VS. CROSS-OVER CABLE CONNECTION
RJ-45 8-pin straight-through
for 10BASE-T/100BASE-TX
signaling
TXP 1
TXN 2
RXP 3
Not Used 4
Not Used 5
RXN 6
Not Used 7
Not Used 8
1 TXP
2 TXN
3 RXP
4 Not Used
5 Not Used
6 RXN
7 Not Used
8 Not Used
Direct Connect Cable
RJ-45 8-pin cross-over for
10BASE-T/100BASE-TX
signaling
TXP 1
TXN 2
RXP 3
Not Used 4
Not Used 5
RXN 6
Not Used 7
Not Used 8
1 TXP
2 TXN
3 RXP
4 Not Used
5 Not Used
6 RXN
7 Not Used
8 Not Used
Cross-Over Cable
DS00001946A-page 84
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