LAN89218 datasheet(69/148 Pages) MICROCHIP

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DS60001255B-page 69

LAN89218

4.8

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 4-3, the LAN89218 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 an internal register 27.15, or the external control pins AMDIX_EN.

When disabled the TX and RX pins can be configured with the Channel Select (CH_SELECT) pin as desired.

Figure 4-3 shows the signal names at the RJ-45 connector, The mapping of these signals to the pins on the

LAN89218 is as follows:

TXP = TPO+

TXN = TPO-

RXP = TPI+

RXN = TPI-

FIGURE 4-3:

DIRECT CABLE CONNECTION VS. CROSS-OVER CABLE CONNECTION

LAN89218 Datasheet(PDF) 69 Page - Microchip Technology