
LU3X54FT
QUAD-FET for 10Base-T/100Base-TX/FX
Data Sheet
July 2000
24
Lucent Technologies Inc.
43
ISET_100
I
Current Set 100 Mbits/s.
 An external resistor (nominally 24.9 k
) is 
placed from this pin to ground to set the 100 Mbits/s TP driver transmit 
output level.
10 MHz Input Clock.
 Optional reference clock for 10 Mbits/s repeater 
mode for phase alignment. When used, TX_CLK will be driven from 
REF10. If not used, let this pin float.
20 MHz Input Clock.
 20 MHz (
±
100 ppm) TTL level clock with 
45%—55% duty cycle. If the internal 20 MHz clock synthesizer is being 
used, ground this pin (default).
Transmit LED[D].
 This pin indicates transmit activity on port D. Exter-
nal buffers are necessary to drive the LEDs. 
Carrier Integrity Enable.
 At powerup or reset, if this pin is pulled high 
through a 4.7 k
 resistor, it will enable the carrier integrity function of 
register 29, bit 3, if station management is unavailable. 
114
REF10
I
27
CLK20
I
166
TXLED[D]/
CARIN_EN
I/O
This pin has an internal 50 k
 pull-down resistor for normal operation 
(CARIN_EN is disabled). This input and register bits [29.3] are ORed 
together.
Transmit LED[C].
 This pin indicates transmit activity on port C. Exter-
nal buffers are necessary to drive the LEDs. 
Encoder/Decoder Bypass.
 At powerup or reset, if this pin is pulled 
high through a 4.7 k
 resistor, it will enable the ENC_DEC_BYPASS 
function of register 29, bit 6, if station management is unavailable.
165
TXLED[C]/
ENC_DEC_BYPASS
I/O
This pin has an internal 50 k
 pull-down resistor for normal operation 
(encoder/decoder ON). This input and the register bit [29.6] are ORed 
together enabling the encoder/decoder bypass function for all four 
channels.
Transmit LED[B].
 This pin indicates transmit activity on port B. Exter-
nal buffers are necessary to drive the LEDs. 
Scrambler/Descrambler Bypass.
 At powerup or reset, this pin may 
be used to enable the SCRAM_DESC_BYPASS function by pulling this 
pin high through a 4.7 k
 resistor, if station management is unavail-
able. This is the same function as register 29, bit 4. 
164
TXLED[B]/
SCRAM_DESC_BYPASS
I/O
This pin has an internal 50 k
 pull-down resistor for normal operation 
(scrambler/descrambler ON). This input and the register bit [29.4] are 
ORed together during powerup and reset.
Transmit LED[A].
 This pin indicates transmit activity on port A. Exter-
nal buffers are necessary to drive the LEDs. 
Reference Select.
 At powerup, this pin may be used to select the 
10 MHz reference input of pin REF10 by pulling it high through a 4.7 k
resistor, if station management is unavailable. This is the same function 
as register 30, bit 2. 
162
TXLED[A]/
REF_SEL
I/O
This pin has an internal 50 k
 pull-down resistor for normal operation 
(REF10 not used). This input and the register bit are ORed together.
Pin Information 
(continued)
Pin Descriptions 
(continued)
Table 7. Miscellaneous Pins
 (continued)
Pin
Signal
Type
Description