5222-DS02-R datasheet(25/76 Pages) BOARDCOM

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Preliminary Data Sheet

BCM5222

7/20/04

Broadcom Corporation

Document 5222-DS02-405-R

Full-Duplex Mode

Page 13

Due to the nature of the Block RXDV mode (bit 9 of MII register 1Bh), which is enabled by default, 10BASE-T loopback does

not function properly. It is necessary to first disable the Block RXDV mode by writing FD00h to the Aux Mode 2 register (1Bh).

FULL-DUPLEX MODE

The BCM5222 supports full-duplex operation. While in full-duplex mode, a transceiver can simultaneously transmit and

receive packets on the cable. The COL signal is never activated when in full-duplex mode. The CRS output is asserted only

during receive packets, not transmit packets.

By default, the BCM5222 powers up in half-duplex mode. When auto-negotiation is disabled, full-duplex operation can be

enabled either by FDX pin control or by an MII register bit (register 0h, bit 8).

When auto-negotiation is enabled in DTE mode, full-duplex capability is advertised by default, but can be overridden by a

write to the Auto-Negotiation Advertisement register (04h).

AUTO-MDIX

The BCM5222 offers Auto-MDIX functioning on both PHYs. This enables the device to automatically adapt the configuration

of the device transmit and receive pins in order to successfully link and transmit with a link partner. During auto-negotiation

and 10/100BASE-TX operation, the BCM5222 normally transmits on TD

± pins and receives on RD± pins. The BCM5222

automatically switches its transmitter to the RD

± pins and its receiver to the TD± pins, if required, in order to communicate

with the remote device. If two devices are connected that both have Auto-MDI/MDIX crossover capability, then a random

algorithm determines which end performs the crossover function.

The Auto-MDI/MDIX crossover feature is a function of auto-negotiation. If the BCM5222 is configured not to perform auto-

negotiation, the feature does not work, and a specific cable, either crossed or straight, is required to ensure the transmit

function at one end of the cable is connected with the receive function at the other end of the cable. This feature is enabled

by default, but can be disabled by setting the MDIX_DIS pin high during power-on reset. This will disable the function on

both PHYs. By setting bit 11 in register 1Ch to a 1, the Auto-MDIX can be disabled for an individual PHY. During operation,

the MDI state can be determined by reading bit 13 of register 1Ch, as indicated in the BCM5222 data sheet. Additionally, a

manual MDI swap can be forced by setting or clearing bit 12 of register 1Ch.

10BASE-T MODE

The same magnetics module used in 100BASE-TX mode can be used to interface to the twisted-pair cable when operating

in 10BASE-T mode. The data is two-level Manchester encoded instead of three-level MLT3, and no scrambling/

descrambling or 4B5B coding is performed. Data and clock rates are decreased by a factor of 10, with the MII interface

signals operating at 2.5 MHz.

5222-DS02-R 数据表(PDF) 25 Page - Broadcom Corporation.

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