LAN8720AI datasheet(26/79 Pages) SMSC

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Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support

Datasheet

Revision 1.4 (08-23-12)

SMSC LAN8720A/LAN8720Ai

DATASHEET

3.3

HP Auto-MDIX Support

HP Auto-MDIX facilitates the use of CAT-3 (10BASE-T) or CAT-5 (100BASE-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 3.4, the device’s Auto-MDIX

transceiver is capable of configuring the TXP/TXN and RXP/RXN 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 via the AMDIXCTRL bit in the Special Control/Status

Indications Register.

Figure 3.4 Direct Cable Connection vs. Cross-over Cable Connection

TXP

TXN

RXP

Not Used

RXN

Not Used

TXP

TXN

RXP

Not Used

RXN

Not Used

Direct Connect Cable

RJ-45 8-pin straight-through

for 10BASE-T/100BASE-TX

signaling

TXP

TXN

RXP

Not Used

RXN

Not Used

TXP

TXN

RXP

Not Used

RXN

Not Used

Cross-Over Cable

RJ-45 8-pin cross-over for

10BASE-T/100BASE-TX

signaling

LAN8720AI 데이터시트(PDF) 26 Page - SMSC Corporation

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