5238-DS03-405-R datasheet(24/76 Pages) BOARDCOM

24 / 76 page

BCM5238

Advance Data Sheet

1/31/03

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

Page 16

10BASE-T Mode

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5238-DS03-405-R

When auto-negotiation is enabled, full-duplex capability is advertised by default but can be overridden by a write to the Auto-

Negotiation Advertisement register (04h).

10BASE-T MODE

The same magnetics module is used to interface the twisted-pair cable in 10BASE-T mode and in 100BASE-TX mode. The

data is two-level Manchester coded instead of three-level MLT3, and no scrambling/descrambling or 4B5B coding is

performed.

ISOLATE MODE

Each transceiver in the BCM5238 can be isolated from the RMII/SMII/S3MII interface. When a transceiver is put into isolate

mode, all RMII/SMII/S3MII input pins (TXD0, SSYNCS, SMII_TXC) are ignored and all SMII/S3MII output pins (RXD0,

SSMII_RSYNC, SSMII_RXC) are set at high impedance. MII management pins (MDC, MDIO,) and analog TD±, RD± pins

operate normally. Writing a 1 to bit 10 of the MII Control register 0 puts the port into isolate mode. Writing a 0 to the same

bit removes it from isolate mode. Upon resetting the chip or resetting the isolated port, the isolate mode is off.

SUPER ISOLATE MODE

When the chip is in super isolate mode, in addition to isolate mode actions, the chip also sets the analog TD± pins to high

impedance. Writing a 1 to bit 3 of the MII register 1Eh puts the port into super isolate mode. Writing a 0 to the same bit

removes it from super isolate mode. Upon resetting the chip or resetting the isolated port, the super isolate mode is off.

AUTO POWER-DOWN MODE

The BCM5238 supports a low power mode called auto power-down mode. Auto power-down mode is enabled by setting bit

5 of shadow register 1Bh. When in this mode, the BCM5238 automatically enters the low power mode if the energy from the

link partner is lost. Similarly, the next time energy is detected, the chip resumes full power mode. When the BCM5238 is in

this low power mode, it wakes up after approximately 2.5 to 5.0 seconds, as determined by bit 4 of shadow register 1Bh, and

sends a link pulse while monitoring energy from the link partner. If energy is detected, the BCM5238 enters full power mode

and establishes link with the link partner. Otherwise, the wake-up mode continues for a duration of approximately 40–

600 ms, as determined by bits [3:0] of shadow register 1Bh before going to low power mode. See Table47onpage 53 for

details of various bits.

JUMBO PACKET MODE

In 100BASE-X mode, the BCM5238 can support jumbo packet sizes. The size of the packet that can be handled reliably

depends on the descrambler lock timer settings and the receive FIFO size. By default, the BCM5238 provides an effective

10 bits receive FIFO to accommodate the minor clock deviations of the link partner. Additionally , the BCM5238 incorporates

5238-DS03-405-R Datasheet(PDF) 24 Page - Broadcom Corporation.