LXT972 Level One, LXT972 Datasheet - Page 11

• Manufacturer Part Number: LXT972
• Description: 3.3V Dual-Speed Fast Ethernet Transceiver Datasheet
• Manufacturer: Level One

Network Media / Protocol
Support
The LXT972 supports both 10BASE-T and 100BASE-TX
Ethernet over twisted-pair.
10/100 Network Interface
The network interface port consists of two differential
signal pairs. Refer to
The LXT972 output drivers generate either 100BASE-TX
or 10BASE-T. When not transmitting data, the LXT972
generates 802.3-compliant link pulses or idle code. Input
signals are decoded either as a 100BASE-TX or 10BASE-
T input, depending on the mode selected. Auto-
negotiation/parallel detection or manual control is used to
determine the speed of this interface.
Twisted-Pair Interface
The LXT972 supports either 100BASE-TX or
10BASE-T connections over 100
Unshielded Twisted Pair (UTP) cable. When operating
at 100 Mbps, the LXT971 continuously transmits and
receives MLT3 symbols. When not transmitting data,
the LXT971 generates “IDLE” symbols.
During 10 Mbps operation, Manchester-encoded data
is exchanged. When no data is being exchanged, the
line is left in an idle state. Link pulses are transmitted
periodically to keep the link up.
Only a transformer, RJ-45 connector, load resistor,
and bypass capacitors are required to complete this
interface. On the transmit side, the LXT972 has an
active internal termination and does not require exter-
nal termination resistors. Level One's patented wave-
shaping technology shapes the outgoing signal to help
reduce the need for external EMI filters. Four slew rate
settings (refer to
to match the output waveform to the magnetic charac-
teristics. On the receive side, the internal impedance is
high enough that it has no practical effect on the exter-
nal termination circuit.
Table 4 on page
Table 3
for specific pin assignments.
8) allow the designer
Category
Fault Detection and Reporting
The LXT972 supports one fault detection and
reporting mechanism. “Remote Fault” refers to a
MAC-to-MAC communication function that is
essentially transparent to PHY layer devices. It is
used only during Auto-Negotiation, and therefore is
applicable only to twisted-pair links. “Far-End Fault”,
on the other hand, is an optional PMA-layer function
that may be embedded within PHY devices. The
LXT972 supports only the Remote Fault Function,
explained in the paragraph that follows.
Remote Fault
Bit 4.13 in the Auto-Negotiation Advertisement
Register is reserved for Remote Fault indications. It
is typically used when re-starting the auto-negotiation
sequence to indicate to the link partner that the link is
down because the advertising device detected a fault.
When the LXT972 receives a Remote Fault indication
from its partner during auto-negotiation it:
• sets bit 5.13 in the Link Partner Base Page
• sets the Remote Fault bit 1.4 in the MII Status
Ability Register, and
Register to pass this information to the local con-
troller.
LXT972 Functional Description
11