DP83848C_07 datasheet(18/82 Pages) NSC

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2.3 PHY Address

The 5 PHY address inputs pins are shared with the

RXD[3:0] pins and COL pin as shown below.

The DP83848C can be set to respond to any of 32 possible

PHY addresses via strap pins. The information is latched

into the PHYCR register (address 19h, bits [4:0]) at device

power-up and hardware reset. The PHY Address pins are

shared with the RXD and COL pins. Each DP83848C or

port sharing an MDIO bus in a system must have a unique

physical address.

The DP83848C supports PHY Address strapping values 0

(<00000>) through 31 (<11111>). Strapping PHY Address

0 puts the part into Isolate Mode. It should also be noted

that selecting PHY Address 0 via an MDIO write to PHYCR

will not put the device in Isolate Mode. See Section 2.3.1for

more information.

For further detail relating to the latch-in timing requirements

of the PHY Address pins, as well as the other hardware

configuration pins, refer to the Reset summary in

Section 6.0.

Since the PHYAD[0] pin has weak internal pull-up resistor

and PHYAD[4:1] pins have weak internal pull-down resis-

tors, the default setting for the PHY address is 00001

(01h).

Refer to Figure 2 for an example of a PHYAD connection to

external components. In this example, the PHYAD strap-

ping results in address 00011 (03h).

2.3.1 MII Isolate Mode

The DP83848C 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 via an MDIO write to PHYCR will not put the

device in the MII isolate mode.

When in the MII isolate mode, the DP83848C 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 DP83848C 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 DP83848C 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 DP83848C is in Isolate mode.

Table 2. PHY Address Mapping

Pin #

PHYAD Function

RXD Function

PHYAD0

COL

PHYAD1

RXD_0

PHYAD2

RXD_1

PHYAD3

RXD_2

PHYAD4

RXD_3

Figure 2. PHYAD Strapping Example

VCC

PHYAD0 = 1

PHYAD1 = 1

PHYAD2 = 0

PHYAD3 = 0

PHYAD4= 0

DP83848C Datasheet(PDF) 18 Page - National Semiconductor (TI)

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