Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support
Datasheet
3.1.1.2
4B/5B Encoding
The transmit data passes from the RMII 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 3.1. 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.
Table 3.1 4B/5B Code Table
CODE
GROUP
RECEIVER
INTERPRETATION
TRANSMITTER
INTERPRETATION
SYM
11110
01001
10100
10101
01010
01011
01110
01111
10010
10011
10110
10111
11010
11011
11100
11101
11111
11000
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
I
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
DATA
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
DATA
IDLE
Sent after /T/R until TXEN
Sent for rising TXEN
J
First nibble of SSD, translated to “0101”
following IDLE, else RXER
10001
01101
K
T
Second nibble of SSD, translated to
“0101” following J, else RXER
Sent for rising TXEN
Sent for falling TXEN
First nibble of ESD, causes de-assertion
of CRS if followed by /R/, else assertion
of RXER
00111
R
Second nibble of ESD, causes
deassertion of CRS if following /T/, else
assertion of RXER
Sent for falling TXEN
00100
00110
H
V
Transmit Error Symbol
Sent for rising TXER
INVALID
INVALID, RXER if during RXDV
Revision 1.4 (08-23-12)
18
SMSC LAN8720A/LAN8720Ai
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