V62SLASH12615-01XE-R datasheet(38/92 Pages) TI1

38 / 92 page

DP83848-EP

SLLSEC6D – SEPTEMBER 2012 – REVISED JUNE 2013

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The basic mode control register (BMCR) at address 00h provides control for enabling, disabling, and

restarting the auto-negotiation process. When auto-negotiation is disabled, 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 operation when the auto-negotiation enable bit is set.

The link speed can be examined through the PHY status register (PHYSTS) at address 10h after a Link is

achieved.

The 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

DP83848 (only the 100BASE-T4 bit is not set since the DP83848 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 remote fault has occurred

•

Whether or not valid link has been established

•

Support for management frame preamble suppression

The ANAR indicates the auto-negotiation abilities to be advertised by the DP83848. 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 (restrict) the technology that is used.

The auto-negotiation link partner ability register (ANLPAR) at address 05h is used to receive the base link

code word as well as all next page code words during the negotiation. Furthermore, the ANLPAR will be

updated to either 0081h or 0021h for parallel detection to either 100 Mb/s or 10 Mb/s respectively.

The auto-negotiation expansion register (ANER) indicates additional auto-negotiation status. The ANER

provides status on:

•

Whether or not a parallel detect fault has occurred

•

Whether or not the link partner supports the next page function

•

Whether or not the DP83848 supports the next page function

•

Whether or not the current page being exchanged by auto-negotiation has been received

•

Whether or not the link partner supports auto negotiation

4.1.3

Auto-Negotiation Parallel Detection

The DP83848 supports the parallel detection function as defined in the IEEE 802.3u specification. Parallel

detection requires both the 10 Mb/s and 100 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 correct

technology in the event that the link partner does not support auto-negotiation but is transmitting link

signals that the 100BASE-TX or 10BASET PMAs recognize as valid link signals.

If the DP83848 completes auto-negotiation as a result of parallel detection, bits 5 and 7 within the

ANLPAR register will be set to reflect the mode of operation present in the link partner. Note that bits 4:0

of the ANLPAR will also be set to 00001 based on a successful parallel detection to indicate a valid 802.3

selector field. Software may determine that negotiation completed via parallel detection by reading a zero

in the link partner auto-negotiation able bit once the auto-negotiation complete bit is set. If configured for

parallel detect mode and any condition other than a single good link occurs then the parallel detect fault

bit will be set.

4.1.4

Auto-Negotiation Restart

Once auto-negotiation has completed, it may be restarted at any time by setting bit 9 (restart auto-

negotiation) of the BMCR to one. If the mode configured by a successful auto-negotiation loses a valid

link, then the auto-negotiation process will resume and attempt to determine the configuration for the link.

This function ensures that a valid configuration is maintained if the cable becomes disconnected.

CONFIGURATION

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