LAN9500 Datasheet, PDF (70/213 Pages) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

LAN950x
FIGURE 5-17:
100BASE-TX DATA PATH
MAC
TX_CLK
100M
PLL
Internal
MII 25 MHz by 4 bits
MII
25MHz 4B/5B 25MHz by Scrambler
by 4 bits _Encoder 5 bits _{and PISO}
NRZI
Converter
NRZI
125 Mbps Serial
MLT-3
Tx
Converter ^MLT-3 Driver
MLT-3
MLT-3 Magnetics
RJ45
MLT-3
CAT-5
5.6.1.1 4B/5B Encoding
The transmit data passes from the MII block to the 4B/5B encoder. This block encodes the data from 4-bit nibbles to 5-
bit symbols (known as “code-groups”) according to Table 5-55. Each 4-bit data-nibble is mapped to 16 of the 32 possible
code-groups. The remaining 16 code-groups are either used for control information or are not valid.
The first 16 code-groups are referred to by the hexadecimal values of their corresponding data nibbles, 0 through F. The
remaining code-groups are given letter designations with slashes on either side. For example, an IDLE code-group is
/I/, a transmit error code-group is /H/, etc.
The encoding process may be bypassed by clearing bit 6 of register 31. When the encoding is bypassed the 5^th transmit
data bit is equivalent to TX_ER.
TABLE 5-55: 4B/5B CODE TABLE
Code Group
SYM
Receiver Interpretation
11110
0
0
0000
DATA
01001
1
1
0001
10100
2
2
0010
10101
3
3
0011
01010
4
4
0100
01011
5
5
0101
01110
6
6
0110
01111
7
7
0111
10010
8
8
1000
10011
9
9
1001
10110
A
A
1010
10111
B
B
1011
11010
C
C
1100
11011
D
D
1101
11100
E
E
1110
Transmitter Interpretation
0
0000
DATA
1
0001
2
0010
3
0011
4
0100
5
0101
6
0110
7
0111
8
1000
9
1001
A
1010
B
1011
C
1100
D
1101
E
1110
DS00001875A-page 70
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