AM79C874VC datasheet(38/60 Pages) AMD

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Am79C874

P R E L I M INARY

Power/Loopback Register (Register 19)

Table 22.

Power/Loopback Register (Register 19)

Reg

Bit

Name

Description

Read/

Write

Default

14:7

Reserved

TP125

Transmit transformer ratio selection:

1 = 1.25:1

0 = 1:1

The default value of this bit is controlled by reset-read value of pin

20.

Low Power Mode

1 = Enable advanced power saving mode.

0 = Disable advanced power saving mode

Note: Under normal operating conditions, this mode should never

be disabled. Power dissipation will exceed data sheet values, as

circuitry for both 10 Mbps and 100 Mbps will be turned on.

Test Loopback

1 = Enable test loopback. Data will be transmitted from MII

interface to clock recovery and loopback to MII received data.

Digital loopback

1 = Enable loopback.

0 = Normal operation.

LP_LPBK

1 = Enable link pulse loopback.

0 = Normal operation.

NLP Link Integrity

Test

1 = In Auto-Negotiation test mode, send NLP instead of FLP in

order to test NLP receive integrity.

0 = Sending FLP in Auto-Negotiation test mode.

Reduce Timer

1 = Reduce time constant for Auto-Negotiation timer.

0 = Normal operation.

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