LXT9880 datasheet(33/118 Pages) INTEL

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Advanced 10/100 Repeater with Integrated Management — LXT9860/9880

Datasheet

Document #: 248987

Revision#: 003

Rev Date: 08/07/01

3.2.2

Forced Operation

A port can be directly configured to operate in either 100BASE-TX or 10BASE-T. When a port is

configured for forced operation, it immediately operates in the selected mode. All links are

established as half-duplex only. As a repeater, the LXT98x0 cannot support full-duplex operation.

3.2.3

Changing Port Speed - Forced

To force a port speed change while operating, the following sequence is required:

• Disable the port(s) to be changed.

• Set PHY Port Control Register to desired speed.

• Perform a Repeater Reset (at Register 144; see Table 83 on page 113. The LXT98x0 does not

read hardware configuration pins).

• Re-enable the port(s).

Note:

Forcing a speed change on any port requires a Repeater Reset.

3.2.4

Link Establishment and Port Connection

Once a port establishes link, the LXT98x0 automatically connects it to the appropriate repeater

state machine. If link loss is detected, the port returns to the auto-negotiation state.

3.2.5

MII Port Configuration

These ports can be set via hardware tie ups/downs to be either 10 Mbps or 100 Mbps. The statistics

for these ports are the same as for the other 10/100 ports, except Isolation, Partition, and Symbol

Error.

3.3

Interface Descriptions

The LXT9880 and LXT9860 devices provide eight and six network interface ports, respectively.

Each port provides a twisted-pair interface. The twisted-pair interface directly supports 100BASE-

TX and 10BASE-T. Ethernet applications and fully complies with IEEE 802.3 standards. A

common termination circuit is used.

3.3.1

Twisted-Pair Interface

The LXT98x0 pinout is optimized for dual-height RJ-45 connectors. The twisted-pair interface for

each port consists of two differential signal pairs — one for transmit and one for receive. The

transmit signal pair is TPOP/TPON, the receive signal pair is TPIP/TPIN.

The transmitter requires magnetics with 1:1 turns ratio. The center tap of the primary side of the

transmit winding must be tied to a quiet VCC for proper operation. When the twisted-pair interface

is disabled, the transmitter outputs are tri-stated.

The receiver requires magnetics with a 1:1 turns ratio, and a load of 100

Ω. When the twisted-pair

port is enabled, the receiver actively biases its inputs to approximately 2.8V. When the twisted-pair

interface is disabled, no biasing is provided. A 4 k

Ω load is always present across the TPIP/TPIN

pair.

LXT9880 Datasheet(PDF) 33 Page - Intel Corporation

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