CS8900-CQ 查看數據表（PDF） - Cirrus Logic

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CS8900-CQ

Highly-Integrated ISA Ethernet Controller

Cirrus Logic 

CS8900

10BASE-T, and 1b or 0b for AUI). During nor-

mal packet reception, Carrier Sense remains

asserted while the frame is being received, and is

de-asserted 1.3 to 2.3 bit times after the last low-

to-high transition of the End-of-Frame (EOF)

sequence. Whenever the receiver is idle (no re-

ceive activity), Carrier Sense is de-asserted. The

CRS bit (Register 14, LineST, Bit E) reports the

state of the Carrier Sense signal.

Clock and Data Recovery

When the receiver is idle, the phase-lock loop

(PLL) is locked to the internal clock signal. The

assertion of the Carrier Sense signal interrupts

the PLL. When it restarts, it locks on the incom-

ing data. The receive clock is then compared to

the incoming data at the bit cell center and any

phase difference is corrected. The PLL remains

locked as long as the receiver input signal is

valid. Once the PLL has locked on the incoming

data, the ENDEC converts the Manchester data

to NRZ and passes the decoded data and the re-

covered clock to the MAC for further processing.

AUIonly

(Bit 8)

0

1

0

AutoAUI/10BT

(Bit 9)

0

N/A

1

Physical

Interface

10BASE-T Only

AUI Only

Auto-Select

Table 3.11. Interface Selection

Interface Selection

Physical interface selection is determined by the

AUIonly bit (Bit 8) and the AutoAUI/10BT bit

(Bit 9) in the LineCTL register (Register 13). Ta-

ble 3.11 describes the possible configurations.

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.

AUI Only: When configured for AUI-only opera-

tion, the AUI and its interface to the ENDEC are

active, and the 10BASE-T transceiver is powered

down.

Auto-Select: In Auto-Select mode, the CS8900

automatically selects the 10BASE-T interface

and powers down the AUI if valid packets and

link pulses are detected by the 10BASE-T re-

ceiver. If valid packets and link pulses are not

detected, the CS8900 selects the AUI. Whenever

the AUI is selected, the 10BASE-T receiver re-

mains active to listen for link pulses or packets.

If 10BASE-T activity is detected, the CS8900

switches back to 10BASE-T.

3.11 10BASE-T Transceiver

The CS8900 includes an integrated 10BASE-T

transceiver that is compliant with the relevant

portions of section 14 of the Ethernet standard

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

and digital circuitry needed to interface the

CS8900 directly to a simple isolation transformer

(see section 11.0 for a connection diagram). Fig-

ure 3.10 provides a block diagram of the

10BASE-T transceiver.

10BASE-T Filters

The CS8900’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

implementations 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 nominal 3 dB cutoff frequency of the

filters is 16 MHz, and the nominal attenuation at

30 MHz (3rd harmonic) is -27 dB.

DS150PP2

31

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