Lexmark T420 User Reference page 130

Set Card Speed
Purpose: The network card is designed to automatically sense the connection speed of your network;
however, you can disable this feature and set the speed manually.
Values:
Auto* - The printer detects current network speed.
10 Megabits per second (Mbps), Half Duplex - Forces the printer to try to connect to the network
only at 10Mbps, Half Duplex.
10Mbps, Full Duplex - Forces the printer to try to connect to the network only at 10Mbps, Full Duplex.
100Mbps, Half Duplex - Forces the printer to try to connect to the network only at 100Mbps, Half
Duplex.
100Mbps, Full Duplex - Force the printer to try to connect to the network only at 100Mbps, Full
Duplex.
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