LAN91C96IQFP datasheet(80/109 Pages) SMSC

80 / 109 page

Non-PCI Single-Chip Full Duplex Ethernet Controller

Rev. 03-28-07

Page 80

SMSC DS – LAN91C96I

DATASHEET

Squelch Function

The integrated smart squelch circuit employs a combination of amplitude and timing measurements to

determine the validity of data received off the network. It prevents noise at the differential inputs from

falsely triggering the decoder in the absence of valid data or link test pulses. Signal levels below 300mV

(180mV for AUI) or pulse widths less than 15ns at the differential inputs are rejected. Signals above

585mV (300mV for AUI) and pulse widths greater than 30ns will be accepted. When using the extended

cable mode with 10BASE-T media which extends beyond the standard limit of 100 meters, the squelch

level can optionally be set to reject signals below 180mV and accept signals above 300mV. If the input

signal exceeds the squelch requirements, the carrier sense output, nCRS, is asserted.

Reverse Polarity Function

In the 10BASE-T mode, the PHY monitors for receiver polarity reversal due to crossed wires and corrects

by reversing the signal internally.

Collision Detection Function

In the 10BASE-T mode, a collision state is indicated when there are simultaneous transmissions and

receptions on the twisted pair link. During a collision state, the nCOLL signal is asserted. If the received

data ends and the transmit control signal is still active, the transmit data is sent to the MAC within 9 bit

times. The nCOLL signal is de-asserted within 9 bit times after the collision terminates. In the AUI mode,

the external transceiver sends a 10MHz signal to the PHY upon detection of a collision.

Link Integrity

The PHY test for a faulty twisted-pair link. In the absence of transmit data, link test pulses are transmitted

every 16+/-8ms after the end of the last transmission or link pulse on the twisted pair medium. If neither

valid data nor link test pulses are received within 10 to 150ms, the link is declared bad and both data

transmission as well as the operational loopback function are disabled. The Link Integrity function can be

disabled for pre-10BASE-T twisted-pair networks.

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