LAN9420 Datasheet, PDF (67/171 Pages) SMSC Corporation – Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface

Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
Datasheet
CODE
GROUP
00101
01000
01100
10000
SYM
V
V
V
V
Table 3.21 4B/5B Code Table (continued)
RECEIVER
INTERPRETATION
INVALID, RX_ER if during RX_DV
INVALID, RX_ER if during RX_DV
INVALID, RX_ER if during RX_DV
INVALID, RX_ER if during RX_DV
TRANSMITTER
INTERPRETATION
INVALID
INVALID
INVALID
INVALID
3.6.1.2
3.6.1.3
3.6.1.4
3.6.1.5
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.
NRZI and MLT3 Encoding
The scrambler block passes the 5-bit wide parallel data to the NRZI converter where it becomes a
serial 125MHz NRZI data stream. The NRZI is encoded to MLT-3. MLT3 is a tri-level code where a
change in the logic level represents a code bit “1” and the logic output remaining at the same level
represents a code bit “0”.
100M Transmit Driver
The MLT3 data is then passed to the analog transmitter, which launches the differential MLT-3 signal,
on outputs TPO+ and TPO-, to the twisted pair media via a 1:1 ratio isolation transformer. The
10BASE-T and 100BASE-TX signals pass through the same transformer so that common “magnetics”
can be used for both. The transmitter drives into the 100Ω impedance of the CAT-5 cable. Cable
termination and impedance matching require external components.
100M Phase Lock Loop (PLL)
The 100M PLL locks onto reference clock and generates the 125MHz clock used to drive the 125 MHz
logic and the 100BASE-Tx Transmitter.
SMSC LAN9420/LAN9420i
67
DATASHEET
Revision 1.6 (07-18-11)