LXT970ATC datasheet(33/74 Pages) INTEL

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Dual-Speed Fast Ethernet Transceiver — LXT970A

Datasheet

2.6.2

100BASE-X Network Operations

During 100BASE-X operation, the LXT970A transmits and receives 5-bit symbols across the

network link. Figure 13 shows the structure of a standard frame packet. When the MAC is not

actively transmitting data, the LXT970A sends out Idle symbols on the line.

In 100TX mode, the LXT970A scrambles the data using a polynomial key, and transmits it to the

network using MLT-3 line code. The MLT-3 signals received from the network are descrambled

and decoded by the LXT970A, and sent across the MII to the MAC.

In 100FX mode, the LXT970A transmits and receives NRZI signals across the pseudo-ECL

interface. An external 100FX transceiver module is required to complete the fiber connection. To

enable 100FX operation, auto-negotiation must be disabled and FX selected.

Figure 13. 100BASE-TX Frame Structure

Figure 14. 100BASE-TX Data Flow

SFD

64-Bit Preamble

(8 Octets)

Start of Frame

Delimiter (SFD)

Destination and Source

Address (6 Octets each)

Packet Length

(2 Octets)

Data Field

(Pad to minimum packet size)

Frame Check Field

(4 Octets)

CRC

InterFrame Gap / Idle Code

(> 12 Octets)

Replaced by

/T/R/ code-groups

End of Stream Delimiter (ESD)

IFG

Replaced by

/J/K/ code-groups

Start of Stream

Delimiter (SSD)

Standard Data Flow

Parallel

Serial

Parallel

4B/5B

MLT3

-1

Transition = 1.

No Transition = 0.

All transitions must follow

pattern: 0, +1, 0, -1, 0, +1...

Scramble

De-

Scramble

Parallel

Serial

Parallel

MLT3

-1

Transition = 1.

No Transition = 0.

All transitions must follow

pattern: 0, +1, 0, -1, 0, +1...

Scramble

De-

Scramble

Symbol (5B) Mode Data Flow

Parallel

Serial

Parallel

MLT3

-1

Transition = 1.

No Transition = 0.

All transitions must follow

pattern: 0, +1, 0, -1, 0, +1...

Scrambler Bypass Data Flow

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