Intel GD82559ER - Manual (Page 17)

Datasheet 11
Networking Silicon —GD82559ER
3.5 PHY Signals
NOTE: 619
Ω
and 549
Ω
for the RBIAS100 and RBIAS10, respectively, are only a recommended values and
should be fine tuned for various designs.
Symbol Type Name and Function
X1 A/I
Crystal Input One. X1 and X2 can be driven by an external 3.3 V 25
MHz crystal. Otherwise, X1 may be driven by an external metal-oxide
semiconductor (MOS) level 25 MHz oscillator when X2 is left floating.
X2 A/O
Crystal Input Two. X1 and X2 can be driven by an external 3.3 V 25
MHz crystal. Otherwise, X1 may be driven by an external MOS level
25 MHz oscillator when X2 is left floating.
TDP
TDN
A/O
Analog Twisted Pair Ethernet Transmit Differential Pair. These
pins transmit the serial bit stream for transmission on the Unshielded
Twisted Pair (UTP) cable. The current-driven differential driver can be
two-level (10BASE-T) or three-level (100BASE-TX) signals depending
on the mode of operation. These signals interface directly with an
isolation transformer.
RDP
RDN
A/I
Analog Twisted Pair Ethernet Receive Differential Pair. These pins
receive the serial bit stream from the isolation transformer. The bit
stream can be two-level (10BASE-T) or three-level (100BASE-TX)
signals depending on the mode of operation.
ACTLED # OUT
Activity LED. The Activity LED pin indicates either transmit or receive
activity. When activity is present, the activity LED is on; when no
activity is present, the activity LED is off.
LILED # OUT
Link Integrity LED. The Link Integrity LED pin indicates link integrity.
If the link is valid in either 10 or 100 Mbps, the LED is on; if link is
invalid, the LED is off.
SPEEDLED # OUT
Speed LED. The Speed LED pin indicates the speed. The speed LED
will be on at 100 Mbps and off at 10 Mbps.
RBIAS100 B
Reference Bias Resistor (100 Mbps). This pin controls the out
envelope of the 82559ERER when transmitting in the 10 Mbps mode
via the use of a pull-down resistor to ground. A value of 619
Ω pull-
down resistor is adequate is most applications.
RBIAS10 B
Reference Bias Resistor (10 Mbps). This pin controls the out
envelope of the 82559ER when transmitting in the 10 Mbps mode via
the use of a pull-down resistor to ground. A value of 549
Ω
pull-down
resistor is adequate is most applications.
VREF B
Voltage Reference. This pin is connected to a 1.25 V ± 1% external
voltage reference generator. To use the internal voltage reference
source, this pin should be left floating.