DP83848I datasheet(16/84 Pages) NSC

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2.0 Configuration

This section includes information on the various configura-

tion options available with the DP83848I. The configuration

options described below include:

— Auto-Negotiation

— PHY Address and LEDs

— Half Duplex vs. Full Duplex

— Isolate mode

— Loopback mode

—BIST

2.1 Auto-Negotiation

The Auto-Negotiation function provides a mechanism for

exchanging configuration information between two ends of

a link segment and automatically selecting the highest per-

formance mode of operation supported by both devices.

Fast Link Pulse (FLP) Bursts provide the signalling used to

communicate Auto-Negotiation abilities between two

devices at each end of a link segment. For further detail

regarding Auto-Negotiation, refer to Clause 28 of the IEEE

802.3u specification. The DP83848I supports four different

Ethernet protocols (10 Mb/s Half Duplex, 10 Mb/s Full

Duplex, 100 Mb/s Half Duplex, and 100 Mb/s Full Duplex),

so the inclusion of Auto-Negotiation ensures that the high-

est performance protocol will be selected based on the

advertised ability of the Link Partner. The Auto-Negotiation

function within the DP83848I can be controlled either by

internal register access or by the use of the AN_EN, AN1

and AN0 pins.

2.1.1 Auto-Negotiation Pin Control

The state of AN_EN, AN0 and AN1 determines whether the

DP83848I is forced into a specific mode or Auto-Negotia-

tion will advertise a specific ability (or set of abilities) as

given in Table 1. These pins allow configuration options to

be selected without requiring internal register access.

The state of AN_EN, AN0 and AN1, upon power-up/reset,

determines the state of bits [8:5] of the ANAR register.

The Auto-Negotiation function selected at power-up or

reset can be changed at any time by writing to the Basic

Mode Control Register (BMCR) at address 0x00h.

2.1.2 Auto-Negotiation Register Control

When Auto-Negotiation is enabled, the DP83848I transmits

the abilities programmed into the Auto-Negotiation Adver-

tisement register (ANAR) at address 04h via FLP Bursts.

Any combination of 10 Mb/s, 100 Mb/s, Half-Duplex, and

Full Duplex modes may be selected.

Auto-Negotiation Priority Resolution:

— (1) 100BASE-TX Full Duplex (Highest Priority)

— (2) 100BASE-TX Half Duplex

— (3) 10BASE-T Full Duplex

— (4) 10BASE-T Half Duplex (Lowest Priority)

The Basic Mode Control Register (BMCR) at address 00h

provides control for enabling, disabling, and restarting the

Auto-Negotiation process. When Auto-Negotiation is dis-

abled, the Speed Selection bit in the BMCR controls

switching between 10 Mb/s or 100 Mb/s operation, and the

Duplex Mode bit controls switching between full duplex

operation and half duplex operation. The Speed Selection

and Duplex Mode bits have no effect on the mode of oper-

ation when the Auto-Negotiation Enable bit is set.

The Link Speed can be examined through the PHY Status

achieved.

The Basic Mode Status Register (BMSR) indicates the set

of available abilities for technology types, Auto-Negotiation

ability, and Extended Register Capability. These bits are

permanently set to indicate the full functionality of the

DP83848I (only the 100BASE-T4 bit is not set since the

DP83848I does not support that function).

The BMSR also provides status on:

— Whether or not Auto-Negotiation is complete

— Whether or not the Link Partner is advertising that a re-

mote fault has occurred

— Whether or not valid link has been established

— Support for Management Frame Preamble suppression

The Auto-Negotiation Advertisement Register (ANAR)

indicates the Auto-Negotiation abilities to be advertised by

the DP83848I. All available abilities are transmitted by

default, but any ability can be suppressed by writing to the

Table 1. Auto-Negotiation Modes

AN_EN

AN1

AN0

Forced Mode

10BASE-T, Half-Duplex

10BASE-T, Full-Duplex

100BASE-TX, Half-Duplex

100BASE-TX, Full-Duplex

AN_EN

AN1

AN0

Advertised Mode

10BASE-T, Half/Full-Duplex

100BASE-TX, Half/Full-Duplex

10BASE-T Half-Duplex

100BASE-TX, Half-Duplex

10BASE-T, Half/Full-Duplex

100BASE-TX, Half/Full-Duplex

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