LXT970ATC datasheet(32/74 Pages) INTEL

32 / 74 page

LXT970A — Dual-Speed Fast Ethernet Transceiver

Datasheet

2.5.2

Monitoring Status via Indicator Pins

The LEDS, LEDR, LEDT, LEDL, and LEDC pins are CMOS digital outputs that drive LEDs.

These pins along with the FDS/MDINT output, can also be used to externally monitor the status of

the LXT970A. The following notes apply to the FDS/MDINT and LED pins:

• LEDR, LEDT and LEDC pulse Low to indicate receive, transmit, and collision activity

respectively. When the LXT970A asserts these signals, it automatically extends them for 100

ms.

• LEDL indicates link status and LEDS indicates link speed. LEDL and LEDS are active Low.

• In its default state (17.1 = 0), the MDINT/FDS output indicates duplex condition. FDS is

active High.

Table 16 shows the state of the LXT970A according to the status of LEDL, LEDS, and FDS pins.

2.6

100BASE-X Operation

2.6.1

100BASE-X MII Operations

The MAC exchanges data with the LXT970A over the MII interface. The LXT970A converts the

digital data from the MAC into an analog waveform that is transmitted to the network via the

copper (TX) or fiber (FX) interface. The LXT970A converts analog signals received from the

network into a digital format and sends them to the MAC via the MII. Refer to the MII interface

discussion on page 20 for details on MII control and data signals.

The 100BASE-X protocol specifies the use of a 5-bit symbol code on the network media. However,

data is normally transmitted across the MII interface in 4-bit nibbles. The LXT970A incorporates a

4B/5B encoder/decoder circuit that translates 4-bit nibbles from the MII into 5-bit symbols for the

100BASE-X connection, and translates 5-bit symbols from the 100BASE-X connection into 4-bit

nibbles for the MII. Figure 14 shows the data conversion flow from nibbles to symbols. Table 17

shows 4B/5B symbol coding (not all symbols are valid).

In some applications it may be desirable to bypass the 4B/5B encoder/decoder circuit, and operate

the MII as a 5-bit symbol mode interface. The LXT970A provides additional lines in both the

receive and transmit channels (RXD4 & TXD4) to accommodate MACs that accept 5-bit symbols.

Table 16. LXT970A Status using FDS/LED Pins

LXT970A State

Pin Status

LEDL

LEDS

FDS

During Power-up

High

Low

During Auto-Negotiation or

Link Failure

High

Low

Link-up; 100 Mbps; full-duplex

Low

High

Link-up; 100 Mbps; half-duplex

Low

Link-up; 10 Mbps; full-duplex

Low

High

Link-up; 10 Mbps; half-duplex

Low

High

Low

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