Scrambling, Datasheet – SMSC LAN9420 User Manual
Page 66
Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
Datasheet
Revision 1.22 (09-25-08)
66
SMSC LAN9420/LAN9420i
DATASHEET
3.6.1.2
Scrambling
Repeated data patterns (especially the IDLE code-group) can have power spectral densities with large
narrow-band peaks. Scrambling the data helps eliminate these peaks and spread the signal power
more uniformly over the entire channel bandwidth. This uniform spectral density is required by FCC
regulations to prevent excessive EMI from being radiated by the physical wiring.
The scrambler also performs the Parallel In Serial Out conversion (PISO) of the data.
10010
8
8 1000
8
1000
10011
9
9 1001
9
1001
10110
A
A 1010
A
1010
10111
B
B 1011
B
1011
11010
C
C 1100
C
1100
11011
D
D 1101
D
1101
11100
E
E 1110
E
1110
11101
F
F 1111
F
1111
11111
I
IDLE
Sent after /T/R until TX_EN
11000
J
First nibble of SSD, translated to “0101”
following IDLE, else RX_ER
Sent for rising TX_EN
10001
K
Second nibble of SSD, translated to
“0101” following J, else RX_ER
Sent for rising TX_EN
01101
T
First nibble of ESD, causes de-assertion
of CRS if followed by /R/, else assertion
of RX_ER
Sent for falling TX_EN
00111
R
Second nibble of ESD, causes de-
assertion of CRS if following /T/, else
assertion of RX_ER
Sent for falling TX_EN
00100
H
Transmit Error Symbol
Sent for rising TX_ER
00110
V
INVALID, RX_ER if during RX_DV
INVALID
11001
V
INVALID, RX_ER if during RX_DV
INVALID
00000
V
INVALID, RX_ER if during RX_DV
INVALID
00001
V
INVALID, RX_ER if during RX_DV
INVALID
00010
V
INVALID, RX_ER if during RX_DV
INVALID
00011
V
INVALID, RX_ER if during RX_DV
INVALID
00101
V
INVALID, RX_ER if during RX_DV
INVALID
01000
V
INVALID, RX_ER if during RX_DV
INVALID
01100
V
INVALID, RX_ER if during RX_DV
INVALID
10000
V
INVALID, RX_ER if during RX_DV
INVALID
Table 3.21 4B/5B Code Table (continued)
CODE
GROUP
SYM
RECEIVER
INTERPRETATION
TRANSMITTER
INTERPRETATION