LXT974/LXT975 — Fast Ethernet 10/100 Quad Transceivers
Figure 12. LXT974/975 Auto-Negotiation Operation
Power-Up, Reset,
Link Failure
Start
Disable
Auto-Negotiation
Enable
0.12 = 0
0.12 = 1
Auto-Neg/Parallel Detection
Check Value
0.12
Go To Forced
Settings
Attempt Auto-
Negotiation
Listen for 100TX
Idle Symbols
Listen for 10T
Link Pulses
YES
NO
Done
Link Set
2.5
100 Mbps Operation
2.5.1
100BASE-X MII Operations
The LXT974/975 encodes and scrambles the data sent by the MAC, and then transmits it using
MLT3 signaling. The LXT974/975 descrambles and decodes MLT3 data received from the
network.
When the MAC is not actively transmitting data, the LXT974/975 sends out Idle symbols.
The 100BASE-X protocol specifies the use of a 5-bit symbol code on the network media.
However, data is normally transmitted across the MII interface in 4-bit nibbles. The LXT974/975
incorporates a 4B/5B encoder/decoder circuit that translates 4-bit nibbles from the MII into 5-bit
symbols for the 100BASE-X connection, and translates 5-bit symbols from the 100BASE-X
connection into 4-bit nibbles for the MII. Table 12 shows the data conversion flow from nibbles to
symbols. Table 19 on page 32 shows 4B/5B symbol coding (not all symbols are valid).
2.5.2
100BASE-X Network Operations
During 100BASE-X operation, the LXT974/975 transmits and receives 5-bit symbols across the
network link. Figure 14 shows the structure of a standard frame packet. When the MAC is not
actively transmitting data, the LXT974/975 sends out Idle symbols on the line.
In 100TX mode, the LXT974/975 scrambles the data and transmits it to the network using MLT-3
line code. The MLT-3 signals received from the network are descrambled and decoded and sent
across the MII to the MAC.
30
Datasheet
INTEL [ INTEL ]
