5228-DS07-R datasheet(40/100 Pages) BOARDCOM

40 / 100 page

BCM5228

Data Sheet

7/12/04

Broa d c om Co rp o r a t i o n

Page 28

HP Auto-MDIX

Document

5228-DS09-405-R

HP AUTO-MDIX

During auto-negotiation and in various operating modes, one end of the link must be configured as an MDI (Media

Independent Interface) crossover so that each transceiver’s transmitter is connected to the other’s receiver. The BCM5228

contains the ability to perform HP Auto-MDIX crossover, thus eliminating the need for crossover cable or cross-wired (MDIX)

ports.

During auto-negotiation and in various operating modes, the BCM5228 normally transmits on TD± and receives on RD±.

When connected via a straight-through cable to another device that does not have HP Auto-MDIX, the BCM5228

automatically switches its transmitter to RD± and its receiver to TD± to communicate with that device. If the link partner also

has HP Auto-MDIX, then a random algorithm determines which end performs the crossover function.

The HP Auto-MDIX feature is implemented in accordance with the IEEE 802.3ab specification. The HP Auto-MDIX crossover

feature is a function of auto-negotiation. Therefore, if the BCM5228 is configured not to perform auto-negotiation, HP Auto-

MDIX crossover does not work, and a specific cable is required to ensure that each transceiver’s transmitter is connected

to the other’s receiver.

The HP Auto-MDIX feature is enabled in hardware by pulling the MDIX_DIS pin low during power-on reset. If enabled by

hardware, this feature can be disabled by setting bit 11 of the MII register 1Ch to 0.

5228-DS07-R 数据表(PDF) 40 Page - Broadcom Corporation.