DP83848JSQSLASHNOPB datasheet(36/84 Pages) TI1

36 / 84 page

VCC

DP83848H, DP83848J, DP83848K, DP83848M, DP83848T

SNLS250E – MAY 2008 – REVISED APRIL 2015

www.ti.com

6.4.4.1

MII Isolate Mode

The DP83848x can be put into MII Isolate mode by writing to bit 10 of the BMCR register or by strapping

in Physical Address 0. It should be noted that selecting Physical Address 0 through an MDIO write to

PHYCR will not put the device in the MII isolate mode.

When in the MII isolate mode, the DP83848x does not respond to packet data present at TXD[3:0],

TX_EN inputs and presents a high impedance on the TX_CLK, RX_CLK, RX_DV, RX_ER, RXD[3:0],

COL, and CRS outputs. When in Isolate mode, the DP83848x will continue to respond to all management

transactions.

While in Isolate mode, the PMD output pair will not transmit packet data but will continue to source

100BASE-TX scrambled idles or 10BASE-T normal link pulses.

The DP83848x can Auto-Negotiate or parallel detect to a specific technology depending on the receive

signal at the PMD input pair. A valid link can be established for the receiver even when the DP83848x is

in Isolate mode.

Figure 6-4. PHYAD Strapping Example

6.4.5

Half Duplex vs Full Duplex

The DP83848x 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.

Because the DP83848x 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 100BASE-TX mode. Because the CSMA/CD protocol does not apply to full duplex operation, the

DP83848x 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.

Detailed Description

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DP83848JSQ/NOPB Datasheet(PDF) 36 Page - Texas Instruments