AM79C874VC datasheet(39/60 Pages) AMD

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Am79C874

P R E L I M INARY

Mode Control Register (Register 21)

Table 23.

Mode Control Register (Register 21)

Reg

Bit

Name

Description

Read/

Write

Default

Reserved

Force_Link_10

1 = Force link up without checking NLP. Forced during local

loopback.

0 = Normal Operation.

Force_Link_100

1 = Ignore link in 100BASE-TX and transmit data. Auto-

Negotiation must be disabled at this time (pin 56 tied low).

0 = Normal Operation.

Jabber Disable

1 = Disable Jabber function in PHY.

0 = Enable Jabber function in PHY.

7_Wire_Enable

1 = Enable 7-wire interface for 10BASE-T operation. This bit is

useful only when the chip is not in PCS bypass mode.

0 = Normal operation.

CONF_ALED

1 = Activity LED only responds to receive operation.

0 = Activity LED responds to receive and transmit operations for

Half Duplex. LED responds to receive activity in Full Duplex

operation.

This bit should be ignored when Register 0.8 is set to 1 or during

repeater mode operation.

LED_SEL

1 = Select NetPHY-1LP device ‘s Standard LED configuration.

0 = Use the Advanced LED configuration.

Set by

LEDRX/

LED_SEL

FEF_DISABLE

0 = Enable far-end-fault generation and detection function.

1 = Disable far-end-fault.

This bit should be ignored when FX mode is disabled.

Set by

TECH[2:0],

FX_SEL,

ANEGA

pins

Force FEF

Transmit

This bit is set to force to transmit Far End Fault (FEF) pattern.

RX_ER_CNT Full When Receive Error Counter is full, this bit will be set to 1.

RO/ RC

Disable

RX_ER_CNT

1 = Disable Receive Error Counter.

0 = Enable Receive Error Counter.

DIS_WDT

1 = Disable the watchdog timer in the decipher.

0 = Enable watchdog timer.

EN_RPBK

1 = Enable remote loopback (MDI loopback for 100BASE-TX).

0 = Disable remote loopback.

EN_SCRM

1 = Enable data scrambling.

0 = Disable data scrambling.

When FX mode is selected, this bit will be forced to 0.

Set by

SCRAM_EN

PCSBP

1 = Bypass PCS.

0 = Enable PC.

Set by

PCSBP pin

FX_SEL

1 = FX mode selected.

0 = Disable FX mode.

Set by

FX_SEL pin

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