Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support

 

 

 

 

Datasheet

 

 

Table 4.1 4B/5B Code Table (continued)

 

 

 

 

 

CODE

 

RECEIVER

 

TRANSMITTER

GROUP

SYM

INTERPRETATION

 

INTERPRETATION

 

 

 

 

 

00111

R

Second nibble of ESD, causes

 

Sent for falling TXEN

 

 

deassertion of CRS if following /T/, else

 

 

 

assertion of RXER

 

 

 

 

 

 

 

00100

H

Transmit Error Symbol

 

Sent for rising TXER

 

 

 

 

 

00110

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

11001

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

00000

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

00001

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

00010

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

00011

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

00101

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

01000

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

01100

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

10000

V

INVALID, RXER if during RXDV

 

INVALID

 

 

 

 

 

4.2.3Scrambling

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 seed for the scrambler is generated from the transceiver address, PHYAD[4:0], ensuring that in multiple-transceiver applications, such as repeaters or switches, each transceiver will have its own scrambler sequence.

The scrambler also performs the Parallel In Serial Out conversion (PISO) of the data.

4.2.4NRZI 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”.

4.2.5100M Transmit Driver

The MLT3 data is then passed to the analog transmitter, which drives the differential MLT-3 signal, on outputs TXP and TXN, to the twisted pair media across 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.

Revision 1.0 (05-28-09)

20

SMSC LAN8720/LAN8720i

 

DATASHEET