Datasheet

DP83848VYB

www.ti.com

SNLS266D –MAY 2007–REVISED APRIL 2013

Refer to Figure 5-2 for an example of AN connections to external components. In this example, the AN

strapping results in Auto-Negotiation disabled with 10/100 Half/Full-Duplex advertised .

The adaptive nature of the LED outputs helps to simplify potential implementation issues of these dual

purpose pins.

Figure 5-2. AN Strapping and LED Loading Example

5.4.2 LED Direct Control

The DP83848VYB provides another option to directly control any or all LED outputs through the LED

Direct Control Register (LEDCR), address 18h. The register does not provide read access to LEDs.

5.5 HALF DUPLEX vs. FULL DUPLEX

The DP83848VYB supports both half and full duplex operation at both 10 Mb/s and 100 Mb/s speeds.

Half-duplex relies on the CSMA/CD protocol to handle collisions and network access. In Half-Duplex

mode, CRS responds to both transmit and receive activity in order to maintain compliance with the IEEE

802.3 specification.

Since the DP83848VYB is designed to support simultaneous transmit and receive activity it is capable of

supporting full-duplex switched applications with a throughput of up to 200 Mb/s per port when operating

in either 100BASE-TX or 100BASE-FX. Because the CSMA/CD protocol does not apply to full-duplex

operation, the DP83848VYB disables its own internal collision sensing and reporting functions and

modifies the behavior of Carrier Sense (CRS) such that it indicates only receive activity. This allows a full-

duplex capable MAC to operate properly.

All modes of operation (100BASE-TX, and 10BASE-T) can run either half-duplex or full-duplex.

Additionally, other than CRS and Collision reporting, all remaining MII signaling remains the same

regardless of the selected duplex mode.

It is important to understand that while Auto-Negotiation with the use of Fast Link Pulse code words can

interpret and configure to full-duplex operation, parallel detection can not recognize the difference between

full and half-duplex from a fixed 10 Mb/s or 100 Mb/s link partner over twisted pair. As specified in the

802.3u specification, if a far-end link partner is configured to a forced full duplex 100BASE-TX ability, the

parallel detection state machine in the partner would be unable to detect the full duplex capability of the

far-end link partner. This link segment would negotiate to a half duplex 100BASE-TX configuration (same

scenario for 10 Mb/s).

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