5222-DS02-R datasheet(24/76 Pages) BOARDCOM

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BCM5222

Preliminary Data Sheet

7/20/04

Broadcom Corporation

Page 12

Operational Description

Document 5222-DS02-405-R

Section 4: Operational Description

RESET

There are two ways to reset the BCM5222. A hardware reset pin is provided that resets all internal nodes in the chip to a

known state. The reset pulse must be asserted for at least 400 ns. Hardware reset should always be applied to the BCM5222

after power-up.

The BCM5222 also has a software reset capability. To perform software reset, a 1 must be written to bit 15 of the MII Control

register. This bit is self-clearing, meaning that a second write operation is not necessary to end the reset. There is no effect

if a 0 is written to the MII Control register reset bit

CLOCK

The BCM5222 requires a 25 MHz clock reference which can be driven by attaching a 25-MHz crystal between the XTALI

and XTALO pins or by connecting an external oscillator to pin XTALI. Connect 22 pF capacitors from each pin to ground

when using a crystal. When using an oscillator, leave XTALO unconnected. The reference clock requires accuracy of at least

± 50 ppm.

ISOLATE MODE

When the BCM5222 is put into isolate mode, all MII inputs (TXD[3:0], TXEN, and TXER) are ignored, and all MII outputs

(TXC, COL, CRS, RXC, RXDV, RXER, and RXD[3:0]) are set to high impedance. Only the MII management pins (MDC,

MDIO) operate normally. Upon resetting the chip, the isolate mode is off. Writing a 1 to bit 10 of the MII Control register puts

the transceiver into isolate mode. Writing a 0 to the same bit removes it from isolate mode.

LOOPBACK MODE

Loopback mode allows in-circuit testing of the BCM5222 chip. All packets sent in through the TXD pins are looped-back

internally to the RXD pins, and are not sent out to the cable. The loopback mode is enabled by writing a 1 to bit 14 of the MII

Control register. To resume normal operation, bit 14 of the MII Control register must be 0.

Incoming packets on the cable are ignored in loopback mode. Because of this, the COL pin is normally not activated during

loopback mode. To test that the COL pin is actually working, the BCM5222 can be placed into collision test mode. This mode

is enabled by writing a 1 to bit 7 of the MII Control register. Asserting TXEN causes the COL output to go high, and

deasserting TXEN causes the COL output to go low.

While in loopback mode, several function bypass modes are also available that can provide a number of different

combinations of feedback paths during loopback testing. These bypass modes include bypass scrambler, bypass MLT3

encoder and bypass 4B5B encoder. All bypass modes can be accessed by writing bits of the Auxiliary Control register (10h).

5222-DS02-R 数据表(PDF) 24 Page - Broadcom Corporation.

5222-DS02-R 数据表(HTML) 24 Page - Broadcom Corporation.

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