LXT974/LXT975 — Fast Ethernet 10/100 Quad Transceivers
2.7.1
Serial LED Output
The LXT974/975 provides a serial LED interface which should be attached to an external shift
register. This interface provides 24 status bits (6 x 4 ports). Each port reports the following
conditions:
• Transmit (T)
0 = Transmit active 1 = Transmit inactive
• Receive (R)
0 = Receive active 1 = Receive inactive
• Link (L)
0 = Link active
1 = Link inactive
1 = Full-Duplex
1 = 10 Mbps
• Duplex (D)
0 = Half-Duplex
• Speed (S)
0 = 100 Mbps
• Collision (C)
0 = Collision active 1 = Collision inactive
LED Data is output on LEDDAT in sets of 24 bits. The serial burst is repeated every 1 ms. A
status change in any bit also triggers an immediate serial burst (following the minimum inter-burst
gap of 10 µs). LEDENA is driven High for the duration of the LEDDAT output.
2.7.2
Per Port LEDs
The LXT974/975 provides three LED outputs for each port (LEDn_0, LEDn_1 and LEDn_2,
where n = port number). These outputs can directly drive LEDs to indicate activity and collision
status. The active Low “on” times are normally extended for improved LED visibility. The on-
time extension can be disabled by setting bit 16.0 = 1.
2.7.2.1
2.7.2.2
2.7.2.3
LEDn_0
In default mode, LED_0 indicates transmitter active. However, LEDn_0 is programmable and may
also be set to indicate receiver active, link, or full-duplex status. Refer to LED Configuration
Register, Table 51 on page 68, for details on programming options.
LEDn_1
In default mode, LED_1 indicates receiver active. However, LEDn_1 is programmable and may
also be set to indicate link status, full-duplex status or operating speed. Refer to LED
Configuration Register, Table 51 on page 68, for details on programming options.
LEDn_2
In default mode, active Low output indicates link up. However, LEDn_2 is programmable and
may also be set to indicate full-duplex status, operating speed or collision. Refer to LED
Configuration Register, Table 51 on page 68, for details on programming options.
38
Datasheet
INTEL [ INTEL ]
