5220-DS02-R datasheet(26/90 Pages) BOARDCOM

26 / 90 page

BCM5220

Preliminary Data Sheet

04/20/04

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

Page 14

Full-Duplex Mode

Document

5220-DS04-405-R

FULL-DUPLEX MODE

The BCM5220 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 BCM5220 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 0, 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).

One of the LED outputs can be modified to signal full-duplex versus half-duplex operation. This capability is enabled by

setting MII register 1Ah, bit 15. In this mode, XMTLED# becomes FDXLED#, where a 1 output indicates half-duplex and a

0 output indicates full-duplex. This value is the inverse of MII register 18h, bit 0. When the FDXLED mode is activated, the

RCVLED# becomes ACTLED#.

100BASE-FX MODE

For 100BASE-FX mode, the BCM5220 transceiver interfaces with an external 100BASE-FX fiber-optic driver and receiver

instead of the magnetics module used with twisted-pair cable. The differential transmit and receive data pairs operate at

PECL voltage levels instead of those required for twisted-pair transmission. The data stream is encoded using two-level

NRZI instead of three-level MLT3. Since scrambling is not used in 100BASE-FX operation, the stream cipher function is

bypassed.

The external fiber-optic receiver detects signal status and passes it into the BCM5220 through the SD

± pins. The SD± pins

select the 100BASE-FX mode.

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.

10BASE-T SERIAL MODE

The BCM5220 supports 10BASE-T serial mode, also known as the 7-wire interface. In this mode, 10BASE-T transmit and

receive packets appear at the MII in serial fashion, at a rate of 10 MHz. Receive packet data is output on RXD (0)

synchronously with RXC. Transmit packet data must be input on TXD (0) synchronously with TXC. Both clocks toggle at

10 MHz.

5220-DS02-R 数据表(PDF) 26 Page - Broadcom Corporation.

5220-DS02-R 数据表(HTML) 26 Page - Broadcom Corporation.

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