DP83953 datasheet(45/90 Pages) NSC

45 / 90 page

6.0 Port Block Functions (Continued)

www.national.com

6.1.1 Magnetics Specifications

This section describes the required magnetics to be used

with RIC2A Twisted pair ports. The new transformer is the

only external magnetics required. In this configuration, a

transformer requires a 1:2 turn ratio on the transmit path

and a 1:1 turn ratio on the receive path. In addition, the

system designer must determine if chokes are necessary.

They may not be when careful layout techniques are

employed.

6.1.2 IEEE Conformance

The RIC2A was tested for IEEE conformance on different

platforms. This testing brought out a number of points that

designers should be aware of when developing a RIC2A

based system. Specifically, designers may want to make

provisions to optimize their systems for conformance to

Receive Noise Immunity and Transmitter Differential Output

Voltage, as these have shown to be the most difficult items

in the specification to meet.

Receiver Differential Noise Immunity

A repeater using the RIC2A may have difficulty meeting all

parameters of Receiver Differential Noise Immunity (IEEE

802.3 section 14.3.1.3.2) without strict layout and design

considerations aimed at reducing the reception of 20, 25

and 30 MHz signals. Even though a system shy of these

specification sections shall function flawlessly in commer-

cial environments, National Semiconductor recommends a

3 pole low-pass Butterworth receive filter with a cut off fre-

quency of 15 MHz for those concerned about full IEEE

compliance. Figure 21 is an example of such a filter. Sys-

tems implementing this filter have been shown to comply

with the noise immunity specification.

Filters like this are often packaged within magnetics mod-

ules. These modules are currently available from Halo, Bel-

fuse, Pulse, and Valor magnetics suppliers. This is a point

for reference only. National Semiconductor does not qualify,

recommend or claim conformance with any such device.

Peak Differential Output Voltage (VOD)

Without any resistive loading on the REQ and RTX pins, a

RIC2A based repeater will pass all conformance tests with

the possible exception of Peak Differential Output Voltage

(VOD into a resistive load). With only one twisted pair port

loaded and transmitting a packet, and with the system run-

ning at 5.25V in a 0oC chamber, the output may marginally

violate the Peak Differential Output Voltage (VOD into a

resistive load) at the upper limit. With all twelve twisted pair

ports loaded and transmitting, and with the system running

at 4.75V in an 80oC chamber, the output may marginally

violate Peak Differential Output Voltage (VOD into a resis-

tive load) at the lower limit.

Please note that this parameter is also related to layout

considerations, so these results may not be observed with

every design. Also, the violation of this specification under

these conditions will not affect a normal network. The

RIC2A has undergone endurance testing in many plat-

forms and has not shown any loss of data attributed to out

of spec VOD.

A discussion of VOD on the RIC2A would not be complete

without the inclusion of comments about the RTX and REQ

pins. The RTX and REQ pins can be used to tune the inter-

nal transmit filter and wave shaping circuitry. The RTX input

can be used to adjust the differential voltage (VOD) of all

output drivers. By placing a resistor between RTX and VDD,

the peak-to-peak Voltage will be increased. Conversely,

Figure 17. AUI Port Connection

DP83953 Datasheet(PDF) 45 Page - National Semiconductor (TI)

DP83953 Datasheet(HTML) 45 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

Datasheet Download

Link URL