LAN91C111 datasheet(68/125 Pages) MICROCHIP

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DS00002276A-page 69

LAN91C111

9.1

9.1.1

RST - RESET

A ‘1’ written to this bit will initiate a reset of the PHY. The bit is self-clearing, and the PHY will return a ‘1’ on reads to this

bit until the reset is completed. Write transactions to this register may be ignored while the PHY is processing the reset.

All PHY registers will be driven to their default states after a reset. The internal PHY is ready for normal operation 50

mS after the RST bit is set. Software driver requires to wait for 50mS after setting the RST bit to high to access the

internal PHY again.

9.1.2

LPBK - Loopback

Writing a ‘1’ will put the PHY into loopback mode.

9.1.3

SPEED (SPEED SELECTION)

When Auto-Negotiation is disabled this bit can be used to manually select the link speed. Writing a ‘1’ to this bit selects

100 Mbps, a ‘0’ selects 10 Mbps.

When Auto-Negotiation is enabled reading or writing this bit has no meaning/effect.

9.1.4

ANEN_EN - AUTO-NEGOTIATION ENABLE

Auto-Negotiation (ANEG) is on when this bit is ‘1’. In that case the contents of bits Speed and Duplex are ignored and

the ANEG process determines the link configuration.

9.1.5

PDN - POWER DOWN

Setting this bit to ‘1’ will put the PHY in PowerDown mode. In this state the PHY will respond to management transac-

tions.

9.1.6

MII_DIS - MII DISABLE

Setting this bit will set the PHY to an isolated mode in which it will respond to MII management frames over the MII

management interface but will ignore data on the MII data interface.

The internal PHY is placed in isolation mode at

power up and reset. It can be removed from isolation mode by clearing the MII_DIS bit in the PHY Control Register. If

necessary, the internal PHY can be enabled by clearing the EXT_PHY bit in the Configuration Register.

9.1.7

ANEG_RST - AUTO-NEGOTIATION RESET

This bit will return 0 if the PHY does not support ANEG or if ANEG is disabled through the ANEG_EN bit. If neither of

the previous is true, setting this bit to ‘1’ resets the ANEG process. This bit is self clearing and the PHY will return a ‘1’

until ANEG is initiated, writing a ‘0’ does not affect the ANEG process.

RST

LPBK

SPEED

ANEG_EN

PDN

MII_DIS

ANEG_RST

DPLX

RW, SC

RW. SC

001

COLST

Reserved

00000000

Note:

This bit must not be set when the device is in external PHY mode.

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