LAN9250 datasheet(213/421 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

DS00001913A-page 213

LAN9250

12.2.2.3

Scrambler and PISO

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 PHY address, ensuring that each PHY will have its own scrambler

sequence. For more information on PHY addressing, refer to Section 12.1.1, "PHY Addressing".

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

12.2.2.4

NRZI and MLT-3 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 then encoded to MLT-3. MLT-3 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”.

12.2.2.5

100M Transmit Driver

The MLT-3 data is then passed to the analog transmitter, which drives the differential MLT-3 signal on output pins TXPx

and TXNx, 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

100

 impedance of the CAT-5 cable. Cable termination and impedance matching require external components.

12.2.2.6

100M Phase Lock Loop (PLL)

The 100M PLL locks onto the reference clock and generates the 125 MHz clock used to drive the 125 MHz logic and

the 100BASE-TX Transmitter.

00110

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

11001

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

00000

/P/

SLEEP, Indicates to receiver that the

transmitter will be going to LPI

Sent due to LPI. Used to tell receiver

before transmitter goes to LPI. Also used

for refresh cycles during LPI.

00001

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

00010

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

00011

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

00101

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

01000

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

01100

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

10000

/V/

INVALID, MII Receive Error (RXER) if

during MII Receive Data Valid (RXDV)

INVALID

TABLE 12-1:

4B/5B CODE TABLE (CONTINUED)

Code Group

Sym

Receiver Interpretation

Transmitter Interpretation

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