AMD

PRELIMINARY

1–93

Am79C981

IMR+ Chip External Components

Figure 6 shows a typical twisted pair port external com-

ponents schematic. The resistors used should have a

1% tolerance to ensure interoperability with 10BASE-T

compliant networks. The filters and pulse transformers

are necessary devices that have a major influence on

the performance and compliance of the 10BASE-T ports

of the repeater. Specifically, the transmitted waveforms

are heavily influenced by the filter characteristics and

the twisted pair receivers employ several criteria to con-

tinuously monitor the incoming signal’s amplitude and

timing characteristics to determine when and if to assert

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

that the values and tolerances of the external compo-

nents 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.

Notes:

1. Compatible filter modules, with a brief description of package type and features are included in the Appendix.

2. The resistor values are recommended for general purpose use and should allow compliance to the 10BASE-T specification

for template fit and jitter performance. However, the overall performance of the transmitter is also affected by the transmit

filter configuration.

17306B-12

1.21K

Ω

100

Ω

61.9

Ω

422

Ω

XMT

Filter

RCV

Filter

Filter &

Transformer

Module

Note 1

Note 2

TXP+

TXD–

TXP–

TXD+

RXD+

RXD–

61.9

Ω

422

Ω

RJ45

Connector

TD+

TD–

RD+

RD–

3

6

1

2

1:1

1:1

Am79C981

Figure 7a. Typical TP Port External Components

17306B-13

DO–

DI+

DI–

CI+

CI–

DO+

Pulse

Transformer

Note 1

40.2

Ω

Optional

ANLG GND

0.1

µF

0.1

µF

AUI

Connector

40.2

Ω

40.2

Ω

40.2

Ω

3

10

5

12

2

9

Am79C981

Notes:

1. Compatible AUI transformer modules, with a brief description of package type and features are included in the Appendix.

2. The differential input DI

± and the CI± pairs are externally terminated by two 40.2 Ω ±1% resistors and one optional common-

mode bypass capacitor. The differential input impedance, ZIDF, and the common-mode input impedance, ZICM, are speci-

fied so that the Ethernet specification for cable termination impedance is met using standard 1% resistor terminators. If SIP

devices are used, 39

Ω is the nearest usable equivalent value.

Figure 7b. Typical AUI Port Components