DP83924 datasheet(17/42 Pages) NSC

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3.0 Detailed Functional Description (Continued)

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control logic is used to select the non-default modes,

instead of pull down resistors, then the level on the strap-

ping pins must be maintained for approximately 10 clocks

after the RESET signal deasserts.

There are 3 different ways to reset the device or ports. One

of them is during power-up. The second method is hard-

ware reset where a low active pulse is applied to the

RESET pin. The third method is software reset of individual

ports by writing a ‘1’ to bit D15 of the port status/control

registers 0000h-0003h. This reset doesn’t reset the device

and doesn’t sample the strap options. Please see register

definitions for details.

3.3.16 On Chip Reference (ROC)

This pin connects to an external precision (1%) resistor to

ground for the on chip reference. The recommended value

of this resistor will be determined when device character-

ization is complete. The user should adjust this value

based on the specific board design. (Estimated range is

between 0-5 k

Ω.)

3.4 Auto-negotiation Block

3.4.17 IEEE 802.3u 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 signaling 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 4TPHY supports two Ethernet

protocols (10Mb/s Half Duplex and 10Mb/s Full Duplex), so

the inclusion of Auto-Negotiation ensures that the highest

performance protocol will be selected based on the ability

of the Link Partner.

Upon hardware reset, RXD[4] is sampled (strapping

option) to determine if Auto-Negotiation is enabled. The

4TPHY uses default register values to advertise its full set

of abilities (10 Mb/s Half Duplex, 10 Mb/s Full Duplex)

unless subsequent software accesses modify the mode.

3.4.18 Auto-Negotiation Register Control

When Auto-Negotiation is enabled, the 4TPHY transmits

the abilities programmed into the Auto-Negotiation Adver-

tisement Register (ANAR) via FLP Bursts. Either 10Mb/s

Half-Duplex or Full Duplex modes may be selected.

The Basic Mode Control/Status Register (BMCR) provides

software with a mechanism to control the operation of the

4TPHY. The status of Auto-Negotiation Enable and Duplex

mode independent of configuration via Auto-Negotiation, or

software may be obtained by reading the BMCR and Port

Status Register (respectively). These bits are valid if Auto-

Negotiation is disabled or after Auto-Negotiation is com-

plete.

The contents of the Auto-Negotiation Link Partner Ability

figure to the highest performance protocol between the

local and far-end ports. If external software needs to find

out the result of Auto_Negotiation, it can determine which

mode has been configured by Auto-Negotiation by compar-

ing the contents of the ANARand ANLPAR registers and

then selecting the technology whose bit is set in both the

ANAR and ANLPAR of highest priority relative to the follow-

ing list. (Please note that 4TPHY does this automatically

and configures itself without need for software. The soft-

ware might be used by management entity etc. to find out

the results of auto-negotiation.)

Auto-Negotiation Priority Resolution:

— 10BASE-T Full Duplex

— 10BASE-T Half Duplex (Lowest Priority)

The BMCR provides control of enabling, disabling, and

restarting of the Auto-Negotiation function. When Auto-

Negotiation is disabled the Duplex Mode bits in the Port

Status Register controls switching between full duplex

operation and half duplex operation. The Duplex Mode bits

have no effect on the mode of operation when the Auto-

Negotiation Enable bit is set.

The BMCR also provides status on:

— Whether Auto-Negotiation is complete.

— Whether the Link Partner is advertising that a remote

fault has occurred.

The Auto-Negotiation Advertisement Register (ANAR) indi-

cates the Auto-Negotiation abilities to be advertised by the

4TPHY. All available abilities are transmitted by default, but

any ability can be suppressed by writing to the ANAR.

Updating the ANAR to suppress an ability is one way for a

management agent to change (force) the technology that is

used.

The

Auto-Negotiation Link

Partner Ability

(ANLPAR) indicates the abilities of the Link Partner as indi-

cated by Auto-Negotiation communication. The contents of

this register are considered valid when the Auto-Negotia-

tion Complete bit is set.

The Auto-Negotiation Expansion Register (ANER) indi-

cates additional Auto-Negotiation status. The ANER pro-

vides status on:

— Whether a Multiple Link Fault has occurred.

— Whether the Link Partner supports the Next Page func-

tion.

— Whether the 4TPHY supports the Next Page function.

(The 4TPHY does support the Next Page function.)

— Whether the current page being exchanged by Auto-Ne-

gotiation has been received.

— Whether the Link Partner supports Auto-Negotiation.

3.4.19 Auto-Negotiation Parallel Detection

The 4TPHY supports the Parallel Detection function as

defined in the IEEE 802.3u specification. Parallel Detection

requires the 10 Mb/s receivers to monitor the receive signal

and report link status to the Auto-Negotiation function.

Auto-Negotiation uses this information to configure the cor-

rect technology in the event that the Link Partner does not

support Auto-Negotiation yet is transmitting link signals

that the 10BASE-T PMAs recognize as valid link signals.

If the 4TPHY completes Auto-Negotiation as a result of

Parallel Detection the appropriate bits inthe ANLPAR reg-

ister will be set to reflect the mode of operation present in

the Link Partner. Software may determine that negotiation

completed via Parallel Detection by reading a zero in the

Link Partner Auto-Negotiation Able bit once the Auto-Nego-

tiation Complete bit is set.

As an example of Parallel Detection, when the Link Partner

supports 10BASE-T full duplex, but does not support Auto-

Negotiation. Parallel Detection will allow the 4TPHY to

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