LXT975B datasheet(37/74 Pages) INTEL

37 / 74 page

Fast Ethernet 10/100 Quad Transceivers — LXT974/LXT975

Datasheet

The LXT974/975 does not support fiber connections at 10 Mbps.

2.6.2.1

Preamble Handling

In 10BASE-T Mode, the LXT974/975 strips the entire preamble off of received packets. CRS is

asserted a few bit times after carrier is detected. RX_DV is held Low for the duration of the

preamble.

When RX_DV is asserted, the very first two nibbles driven by the LXT974/975 are the SFD “5D”

hex followed by the body of the packet. In 10T loopback, the LXT974/975 loops back whatever

the MAC transmits to it, including the preamble.

2.6.2.2

Link Test

In 10 Mbps mode, the LXT974/975 always transmit link pulses. If the link test function is enabled,

it monitors the connection for link pulses. Once link pulses are detected, data transmission are

enabled and remain enabled as long as either the link pulses or data transmission continues. If the

link pulses stop, the data transmission is disabled.

If the link test function is disabled, the LXT974/975 transmits to the connection regardless of

detected link pulses. The link test function can be disabled by setting bit 19.8 = 1 or by setting

AUTOENA to disable auto-negotiation and setting CFG_1 input High.

2.6.2.3

Link Failure

Link failure occurs if Link Test is enabled and link pulses or packets stop being received. If this

condition occurs, the LXT974/975 returns to the auto-negotiation phase if auto-negotiation is

enabled.

2.6.2.4

SQE (Heartbeat)

By default, the SQE (heartbeat) function is disabled on the LXT974/975. To enable this function,

set bit 19.10 =1. When this function is enabled, the LXT974/975 asserts its COL output after each

transmit packet. See Figure 32 on page 58 for SQE timing parameters.

2.6.2.5

Jabber

If MAC transmission exceeds the jabber timer, the LXT974/975 disables the transmit and loopback

functions and enables the COL pin. See Figure 33 on page 59 for jabber timing parameters.

The LXT974/975 automatically exits jabber mode after the unjab time has expired. This function

can be disabled by setting bit 19.9 = 1.

2.7

LED Functions

The LXT974/975 provides three programmable LEDs per port. Refer to Table 51 on page 68 for

LED programming details. The LXT974/975 also provides a serial LED output.

LXT975B Datasheet(PDF) 37 Page - Intel Corporation