Fast Ethernet 10/100 Quad Transceivers — LXT974/LXT975
2.0
Functional Description
2.1
Introduction
The LXT974 and LXT975 are four-port Fast Ethernet 10/100 Transceivers that support 10 Mbps
and 100 Mbps networks. They comply with all applicable requirements of IEEE 802.3. Each port
can directly drive either a 100BASE-TX line (>130 meters) or a 10BASE-T line (>185 meters).
Figure 4 shows the LXT974 in a typical switch application.
Figure 4. LXT974 Switch Application
Fiber
Module
Backplane
Fiber
Module
LXT974
10/100
Quad Transceiver
Switch
MAC ASIC
Memory
Fiber
Module
Fiber
Module
LXT974
10/100
LXT974
10/100
Quad Transceiver
Quad Transceiver
QUAD
QUAD
Transformer
Transformer
Single RJ-45
Selectable 10 or 100 Mbps
On power-up, the LXT974/975 uses auto-negotiation/parallel detection on each port to
automatically determine line operating conditions. If the PHY device on the other side of the link
supports auto-negotiation, the LXT974/975 auto-negotiates with it using Fast Link Pulse (FLP)
Bursts. If the PHY partner does not support auto-negotiation, the LXT974/975 automatically
detects the presence of either link pulses (10 Mbps PHY) or Idle symbols (100 Mbps PHY) and set
its operating conditions accordingly.
The LXT974/975 interfaces to four 10/100 Media Access Controllers (MAC)s through the MII
interfaces. It performs all functions of the Physical Coding Sublayer (PCS) and Physical Media
Attachment (PMA) sublayer as defined in the IEEE 802.3 100BASE-X specification. This device
also performs all functions of the Physical Media Dependent (PMD) sublayer for 100BASE-TX
connections. The MII speeds are automatically set once port operating conditions have been
determined.
The LXT974/975 provides half-duplex and full-duplex operation at 100 Mbps and 10 Mbps. It also
offers standard Loopback Mode for switch applications. The LXT974/975 supports the 802.3
MDIO register set. Specific bits in the registers are referenced using an “X.Y” notation, where X is
the register number (0-6 or 16-20) and Y is the bit number (0-15).
The LXT975 is pin compatible with the LXT974 except for the network ports. Each port on the
LXT974 provides a combination twisted-pair or PECL interface for a 10/100BASE-TX or
100BASE-FX connection.
The LXT975 is optimized for stacked RJ-45 modular applications as shown in Figure 5. Ports 1
and 3 support the PECL interface for fiber connections and all four ports support the twisted-pair
interface for 10/100BASE-TX connections.
Datasheet
19
INTEL [ INTEL ]
