lan8720 Standard Microsystems Corp., lan8720 Datasheet - Page 19

• Manufacturer Part Number: lan8720
• Description: Small Footprint Rmii 10/100 Ethernet Transceiver With Hp Auto-mdix Support
• Manufacturer: Standard Microsystems Corp.

Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support
Datasheet
SMSC LAN8720/LAN8720i
4.2.2
GROUP
CODE
01001
10100
10101
01010
01011
10010
10011
10110
11010
11000
10001
01101
01110
10111
11011
11100
11101
11110
01111
11111
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
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
Note that encoding can be bypassed only when the MAC interface is configured to operate in MII
mode.
SYM
A
B
C
D
E
0
1
2
3
4
5
6
7
8
9
F
K
T
J
I
th
IDLE
First nibble of SSD, translated to “0101”
following IDLE, else RXER
Second nibble of SSD, translated to
“0101” following J, else RXER
First nibble of ESD, causes de-assertion
of CRS if followed by /R/, else assertion
of RXER
transmit data bit is equivalent to TXER.
A
B
C
D
E
0
1
2
3
4
5
6
7
8
9
F
INTERPRETATION
Table 4.1 4B/5B Code Table
RECEIVER
0000
0001
0010
0011
0100
0101
0110
1000
1001
1010
1011
1100
1101
0111
1110
1111
DATASHEET
19
DATA
Sent after /T/R until TXEN
Sent for rising TXEN
Sent for rising TXEN
Sent for falling TXEN
A
B
C
D
E
0
1
2
3
4
5
6
7
8
9
F
Table
INTERPRETATION
TRANSMITTER
4.1. Each 4-bit data-nibble
0000
0001
0010
0100
0101
1000
1001
1010
0011
0110
0111
1011
1100
1101
1110
1111
Revision 1.0 (04-15-09)
DATA