CS8900A
Crystal LAN™ ISA Ethernet Controller
LinkOK
(to MAC)
10BASE-T Transceiver
Link Pulse
Detector
RX Squelch
RXSQL
RX
RXD-
RXD+
RX
Comparator
RX Filters
ENDEC
TXD-
TX
TX Pre-
Distortion
TX Filters
TX Drivers
TXD+
Filter Tuning
Figure 13. 10BASE-T Transceiver
3.10.4 Interface Selection
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.
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.
3.11 10BASE-T Transceiver
AUIonly
(Bit 8)
AutoAUI/10BT
(Bit 9)
Physical
Interface
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.
0
1
0
0
N/A
1
10BASE-T Only
AUI Only
Auto-Select
Table 11. Interface Selection
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.
3.11.1 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.
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
CIRRUS LOGIC PRODUCT DATA SHEET
DS271PP3
35
CIRRUS [ CIRRUS LOGIC ]
