Figure 3.25 100base-tx data path, 1 100base-tx transmit, Table 3.21 4b/5b code table – SMSC LAN9420 User Manual
Page 65: 100base-tx transmit, 4b/5b encoding, Datasheet
Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
Datasheet
SMSC LAN9420/LAN9420i
65
Revision 1.22 (09-25-08)
DATASHEET
Figure 3.25 100BASE-TX Data Path
3.6.1
100BASE-TX Transmit
The data path of the 100BASE-TX is shown in
. Each major block is explained below.
3.6.1.1
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
. 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 3.21 4B/5B Code Table
CODE
GROUP
SYM
RECEIVER
INTERPRETATION
TRANSMITTER
INTERPRETATION
11110
0
0
0000 DATA
0
0000 DATA
01001
1
1
0001
1
0001
10100
2
2
0010
2
0010
10101
3
3
0011
3
0011
01010
4
4
0100
4
0100
01011
5
5
0101
5
0101
01110
6
6 0110
6
0110
01111
7
7 0111
7
0111
MAC
Tx
Driver
MLT-3
Converter
NRZI
Converter
4B/5B
Encoder
Magnetics
CAT-5
RJ45
100M
PLL
Internal
MII 25 MHz by 4 bits
TX_CLK
25MHz by
5 bits
NRZI
MLT-3
MLT-3
MLT-3
MLT-3
Scrambler
and PISO
125 Mbps Serial
MII
25MHz
by 4 bits