CS8900A datasheet(35/128 Pages) CIRRUS

35 / 128 page

DS271PP3

CS8900A

Crystal LAN™ ISA Ethernet Controller

CIRRUS LOGIC PRODUCT DATA SHEET

3.10.4 Interface Selection

Physical interface selection is determined by AUI-

only bit (Bit 8) and the AutoAUI/10BT (Bit 9) in

the LineCTL register (Register 13). Table 11 de-

scribes the possible configurations.

3.10.4.1 10BASE-T Only

When configured for 10BASE-T only operation,

the 10BASE-T transceiver and its interface to the

ENDEC are active, and the AUI is powered down.

3.10.4.2 AUI Only

When configured for AUI-only operation, the AUI

and its interface to the ENDEC are active, and the

10BASE-T transceiver is powered down.

3.10.4.3 Auto-Select

In Auto-Select mode, the CS8900A automatically

selects the 10BASE-T interface and powers down

the AUI if valid packets or link pulses are detected

by the 10BASE-T receiver. If valid packets and

link pulses are not detected, the CS8900A selects

the AUI. Whenever the AUI is selected, the

10BASE-T receiver remains active to listen for link

pulses or packets. If 10BASE-T activity is detect-

ed, the CS8900A switches back to 10BASE-T.

3.11 10BASE-T Transceiver

The CS8900A includes an integrated 10BASE-T

transceiver that is compliant with the relevant por-

tions of section 14 of the Ethernet standard

(ISO/IEC 8802-3, 1993). It includes all analog and

digital circuitry needed to interface the CS8900A

directly to a simple isolation transformer (see

Section 7.5 on page 120 for a connection diagram).

Figure 13 provides a block diagram of the

10BASE-T transceiver.

3.11.1 10BASE-T Filters

The CS8900A’s 10BASE-T transceiver includes

integrated low-pass transmit and receive filters,

eliminating the need for external filters or a fil-

ter/transformer hybrid. On-chip filters are gm/c im-

plementations of fifth-order Butterworth low-pass

filters. Internal tuning circuits keep the gm/c ratio

tightly controlled, even when large temperature,

supply, and IC process variations occur. The nom-

inal 3 dB cutoff frequency of the filters is 16 MHz,

and the nominal attenuation at 30 MHz (3rd har-

monic) is -27 dB.

AUIonly

(Bit 8)

AutoAUI/10BT

(Bit 9)

Physical

Interface

10BASE-T Only

N/A

AUI Only

Auto-Select

Table 11. Interface Selection

RXSQL

Link Pulse

Detector

TX Pre-

Distortion

RX Squelch

Comparator

TX Filters

Filter Tuning

RX Filters

TX Drivers

RXD-

RXD+

TXD-

TXD+

ENDEC

LinkOK

(to MAC)

10BASE-T Transceiver

Figure 13. 10BASE-T Transceiver

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