DP83849ID datasheet(49/98 Pages) NSC

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7.1.1 Basic Mode Control Register (BMCR)

Table 20. Basic Mode Control Register (BMCR), address 00h

Bit

Bit Name

Default

Description

RESET

0, RW/SC

Reset:

1 = Initiate software Reset / Reset in Process.

0 = Normal operation.

This bit, which is self-clearing, returns a value of one until the reset

process is complete. The configuration is re-strapped.

LOOPBACK

0, RW

Loopback:

1 = Loopback enabled.

0 = Normal operation.

The loopback function enables MII transmit data to be routed to the MII

receive data path.

Setting this bit may cause the descrambler to lose synchronization and

produce a 500

µs “dead time” before any valid data will appear at the

MII receive outputs.

SPEED SELEC-

TION

Strap, RW

Speed Select:

When auto-negotiation is disabled writing to this bit allows the port

speed to be selected.

1 = 100 Mb/s.

0 = 10 Mb/s.

AUTO-NEGOTI-

ATION

ENABLE

Strap, RW

Auto-Negotiation Enable:

Strap controls initial value at reset.

If FX is enabled (FX_EN = 1), then this bit will be reset to 0.

1 = Auto-Negotiation Enabled - bits 8 and 13 of this register are ig-

nored when this bit is set.

0 = Auto-Negotiation Disabled - bits 8 and 13 determine the port speed

and duplex mode.

POWER DOWN

0, RW

Power Down:

1 = Power down.

0 = Normal operation.

Setting this bit powers down the PHY. Only the register block is en-

abled during a power down condition. This bit is OR’d with the input

from the PWRDOWN_INT pin. When the active low PWRDOWN_INT

pin is asserted, this bit will be set.

ISOLATE

0, RW

Isolate:

1 = Isolates the Port from the MII with the exception of the serial man-

agement.

0 = Normal operation.

RESTART

AUTO-NEGOTI-

ATION

0, RW/SC

Restart Auto-Negotiation:

1 = Restart Auto-Negotiation. Re-initiates the Auto-Negotiation pro-

cess. If Auto-Negotiation is disabled (bit 12 = 0), this bit is ignored. This

bit is self-clearing and will return a value of 1 until Auto-Negotiation is

initiated, whereupon it will self-clear. Operation of the Auto-Negotiation

process is not affected by the management entity clearing this bit.

0 = Normal operation.

DUPLEX MODE

Strap, RW

Duplex Mode:

When auto-negotiation is disabled writing to this bit allows the port Du-

plex capability to be selected.

1 = Full Duplex operation.

0 = Half Duplex operation.

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