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Cortina Systems LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
LXT9785/LXT9785E
Datasheet
249241, Revision 11.0
16 April 2007
4.9 100 Mbps Operation
4.9.2.1.1
Preamble Handling
When the MAC asserts TxEN, the PCS substitutes a /J/K/ symbol pair, also known as the
Start-of-Stream Delimiter (SSD), for the first two nibbles received across the RMII. The
PCS layer continues to encode the remaining RMII data until TxEN is de-asserted (see
The PCS layer performs the opposite function in the receive direction by substituting two
preamble nibbles for the SSD.
4.9.3
PMA Sublayer
The 100BASE-X PMA protocol uses the 4B/5B data encoding scheme to encode/decode
the data streams. The coding scheme is shown in
Table 46.
Figure 28
Protocol Sublayers
Encoder/Decoder
Serializer/De-serializer
Link/Carrier Detect
PCS
Sublayer
PMA
Sublayer
MII Interface
LVPECL Interface
Fiber Transceiver
LXT9785
100BASE-TX
100BASE-FX
Scrambler/
De-scrambler
PMD
Sublayer
Table 46
4B/5B Coding
Code Type
4B Code
3 2 1 0
Name
5B Code
4 3 2 1 0
Interpretation
0 0 0 0
0
1 1 1 1 0
Data 0
0 0 0 1
1
0 1 0 0 1
Data 1
0 0 1 0
2
1 0 1 0 0
Data 2
0 0 1 1
3
1 0 1 0 1
Data 3
0 1 0 0
4
0 1 0 1 0
Data 4
0 1 0 1
5
0 1 0 1 1
Data 5
1. The /I/ (Idle) code group is sent continuously between frames.
2. The /J/ and /K/ (SSD) code groups are always sent in pairs; /K/ follows /J/.
3. The /T/ and /R/ (ESD) code groups are always sent in pairs; /R/ follows /T/.
4. An /H/ (Error) code group is used to signal an error condition.