LXT971ABC datasheet(38/90 Pages) INTEL

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LXT971A 3.3V Dual-Speed Fast Ethernet Transceiver

Datasheet

Document #: 249414

Revision #: 002

Rev. Date: August 7, 2002

3.7.2

Collision Indication

Figure 18 shows normal transmission. Upon detection of a collision, the COL output is asserted

and remains asserted for the duration of the collision as shown in Figure 19.

3.7.3

100BASE-X Protocol Sublayer Operations

With respect to the 7-layer communications model, the LXT971A is a Physical Layer 1 (PHY)

device. The LXT971A implements the Physical Coding Sublayer (PCS), Physical Medium

Attachment (PMA), and Physical Medium Dependent (PMD) sublayers of the reference model

defined by the IEEE 802.3u standard. The following paragraphs discuss LXT971A operation from

the reference model point of view.

3.7.3.1

PCS Sublayer

The Physical Coding Sublayer (PCS) provides the MII interface, as well as the 4B/5B encoding/

decoding function.

For 100BASE-TX and 100FX operation, the PCS layer provides IDLE symbols to the PMD-layer

line driver as long as TX_EN is de-asserted.

3.7.3.1.1 Preamble Handling

When the MAC asserts TX_EN, the PCS substitutes a /J/K symbol pair, also known as the Start-of-

Stream Delimiter (SSD), for the first two nibbles received across the MII. The PCS layer continues

to encode the remaining MII data, following the coding in Table 11, until TX_EN is de-asserted. It

then returns to supplying IDLE symbols to the line driver.

Figure 18. 100BASE-TX Transmission with No Errors

Figure 19. 100BASE-TX Transmission with Collision

DA DA DA DA DA

DA DA

TX_CLK

TX_EN

TXD<3:0>

CRS

COL

JAM

TX_CLK

TX_EN

TXD<3:0>

CRS

COL

JAM

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