10

Am79C98

In both modes, the jabber circuitry, collision detection,

and collision oscillator functions are disabled and the

AUI and RXD+/– squelch circuits are active.

TPEX External Components

Figure 1 shows a typical twisted-pair port external

components schematic. The resistors used should

have a

±1% tolerance to ensure interoperability with

10BASE-T-compliant networks. Filters and pulse trans-

formers are necessary devices that have a major influ-

ence on the performance and compliance of a TPEX-

based MAU. Specifically, the transmitted waveforms

are heavily influenced by filter characteristics and the

twisted-pair receivers employ several criteria to contin-

uously monitor the incoming signal’s amplitude and

timing characteristics to determine when and if to as-

sert the internal carrier sense. For these reasons, it is

crucial that the values and tolerances of the external

components be as specified. Several manufacturers

produce a module that combines the functions of the

transmit and receive filters and the pulse transformers

into one package.

Note:

The filter/transformer module shown is available from the following manufacturers: Belfuse, TDK, Pulse Engineering, PCA, Valor

Electronics, and Nano Pulse.

Figure 1.

Typical Twisted-Pair Port External Components

14395D-5

57.6

324.0

768.0

57.6

324.0

100

Ω

Am79C100

TPEX

TXD+

TXP+

TXD–

TXP–

RXD+

RXD–

XMIT

Filter

RECV

Filter

1:1

1:1

TD+

TD–

RD+

RD–

Twisted-Pair

Cable

Module