DP83858VF datasheet(22/37 Pages) NSC

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5.2 Repeater ID Interface

The repeater ID interface is shown in Figure 6. It consists

of a bank of DIP switches or links to set the RID number for

the DP83858 to use as its IR_VECT[4:0] number.

5.3 Inter Repeater Bus Connections

For a simple stand-alone repeater that cannot be stacked,

no inter repeater bus transceivers/drivers are required and

the inter repeater bus interface is simple. An example of

this is shown in Figure 7.

For a stackable hub design, the DP83858's Inter Repeater

Bus connections are complex and have many issues

regarding signal timing, loading and layout. An example

design for a TTL level inter repeater bus is given in

Figure 8. It should be noted that this a single example of

possible connections to an inter repeater bus. There are

many other possible ways to design this interface. Design-

ers should be aware that timing, particularly skew between

clock and data, is critical. For this reason, the use of LS, S,

TTL, or CMOS logic drivers is not recommended. The ABT

family of logic is recommended, as well as the FAST® fam-

ily could possibly be made to work too. Also recommended

is the BTL logic transceiver family: this approach has the

advantage of signiﬁcantly lower noise and may assist in

successful passing of FCC and other EMI tests.

Figure 8 shows the signal connections on the Inter-RIC

bus. The pull up resistors on the DP83858 should be a

minimum of 1.2 k

Ω.

Lower values may be required

depending on layout/loading, especially on the /ACTIVEO

and /IR_ACTIVE signals where short deassertion time is

critical. The value of the pull up resistor terminations on

the inter repeater bus backplane will depend upon the bus

loading. The values should be chosen so that the signals

on the bus have fast enough edges to meet the DP83858

inter repeater bus timings. The inter repeater bus will need

to be terminated properly at each end to prevent signal

reﬂections from causing problems.

Figure 6. DP83858 Repeater ID Number Interface

Figure 7. DP83858 Stand-alone Inter Repeater Bus Interface

+5V

RID4

RID3

RID2

RID1

RID0

DIP

Switches

4.7K

ohm

Pull up

resistors

DP83858

100RIC8

VCC

IR_VECT4

/ACTIVEO

/IR_COL_OUT

/IR_COL_IN

/IR_ACTIVE

IR_VECT3

IR_VECT2

IR_VECT1

IR_VECT0

DP83858

100RIC8

IRD3

IRD2

IRD1

IRD0

IRD_CK

/IRD_V

/IRD_ER

MD3

MD2

MD1

MD0

MD_CK

/MD_V

/MD_ER

IRD_ODIR

1.2Kohm

Pull-Ups

DP83858VF Datasheet(PDF) 22 Page - National Semiconductor (TI)

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