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Datasheet 39
Networking Silicon — 82555
9.0 LED Descriptions
The 82555 supports four LED pins to indicate link status, network activity and network speed.
•
Link: This LED is off (logic high) until a valid link has been detected. After a valid link has
been detected, the LED will remain on (active-low).
•
Activity: This LED is on (active-low) when activity is detected on the wire. In DTE (adapter)
mode, this LED is on during transmit and receive when the 82555 is not in loopback mode. In
repeater mode, this LED is on only during receive when the 82555 is not in loopback mode.
•
Speed: This LED will be on if a 100BASE-TX link is detected and off if a 10BASE-T link is
detected. If the link fails while in Auto-Negotiation, this LED will keep the last valid link state.
If 100BASE-TX link is forced this LED will be on, regardless of the link status. This LED will
be of if the 10BASE-T link is forced, regardless of the link status.
•
Full Duplex: The FDX_N signal can operate as a LED if it is enabled. It indicates full duplex
link for either 100BASE-TX or 10 BASE-T technology.
MDI register 27 in Section 7.2.3.9, “Register 27: 82555 Special Control Bit Definitions” on
page 34 details the information for LED function mapping and support enhancements.