
Advanced 10/100 Repeater with Integrated Management
—
LXT9860/9880
Datasheet
Document #: 248987
Revision#: 003
Rev Date: 08/07/01
33
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
. 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
load is always present across the TPIP/TPIN
pair.