Fast Ethernet 10/100 Quad Transceivers — LXT974/LXT975
In 100FX mode, the LXT974/975 transmits and receives NRZI signals across the PECL interface.
An external 100FX transceiver module is required to complete the fiber connection.
As shown in Figure 14, the MAC starts each transmission with a preamble pattern. As soon as the
LXT974/975 detects the start of preamble, it transmits a J/K symbol (Start of Stream Delimiter,
SSD) to the network. It then encodes and transmits the rest of the packet, including the balance of
the preamble, the Start of Frame Delimiter (SFD), packet data, and CRC. Once the packet ends,
the LXT974/975 transmits the T/R symbol End-of-Stream Delimiter (ESD) and then returns to
transmitting Idle symbols.
Figure 13. 100BASE-TX Data Flow
Standard MII Mode Data Flow
+1
Parallel
D0
to
0
0
0
Serial
Scramble
D1
4B/5B
5B/4B
-1
MLT3
D0 D1 D2 D3
S0 S1 S2 S3 S4
De-
Scramble
D2
D3
Transition = 1.
No Transition = 0.
All transitions must follow
pattern: 0, +1, 0, -1, 0, +1...
Serial
to
Parallel
1. Four independent MII ports serve four independent Network ports. Network port configurations are independently
selectable. MII port speed is set to match the associated Network port.
2. The Scrambler can be bypassed by setting 19.3 = 1.
Figure 14. 100BASE-TX Frame Structure
64-Bit Preamble
(8 Octets)
Destination and Source
Address (6 Octets each)
Packet Length
(2 Octets)
Data Field
(Pad to minimum packet size)
Frame Check Field InterFrame Gap / Idle Code
(4 Octets)
(> 12 Octets)
CRC
IFG
SFD
P0 P1 P6
DA DA SA SA L1
L2 D0 D1 Dn
I0
Replaced by
/T/R/ code-groups
End of Stream Delimiter (ESD)
Replaced by
Start of Frame
Delimiter (SFD)
/J/K/ code-groups
Start of Stream
Delimiter (SSD)
Datasheet
31
INTEL [ INTEL ]
