CS8920A View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
'CS8920A' PDF : 144 Pages View PDF
CS8920A
the CS8920A automatically corrects a reversal. If
the PolarityDis bit is set, the CS8920A does not
correct a reversal. The PolarityOK bit and the
PolarityDis bit are independent.
To detect a reversed pair, the receiver examines
received link pulses and the End-of-Frame
(EOF) sequence of incoming packets. If it de-
tects at least one reversed link pulse and at least
four frames in a row with negative polarity after
the EOF, the receive pair is considered reversed.
Any data received before the correction of the
reversal is ignored.
Collision Detection
If half-duplex operation is selected (Register 1D,
Bit E, ForceFDX), the CS8920A detects a
10BASE-T collision whenever the receiver and
transmitter are active simultaneously. When a
collision is present, the Collision Detection cir-
cuit informs the MAC by asserting the internal
Collision signal (see section 3.11 for collision
handling).
3.13 Attachment Unit Interface (AUI)
The CS8920A Attachment Unit Interface (AUI)
provides a direct interface to external 10BASE2,
10BASE5, and 10BASE-FL Ethernet transceiv-
ers. It is fully compliant with Section 7 of the
Ethernet standard (ISO/IEC 8802-3), and as
such, is capable of driving a full 50-meter AUI
cable.
The AUI consists of three pairs of signals: Data
Out (DO+/DO-), Data In (DI+/DI-), and Colli-
sion In (CI+/CI-). To select the AUI, the host
should set the AUI bit (Register 13, LineCTL,
Bit 8). The AUI can also be selected automat-
ically as described in the previous section.
Figure 3.12 provides a block diagram of the
AUI. (For a connection diagram, see section
12.0).
DS238PP2
AUI Transmitter
The AUI transmitter is a differential driver de-
signed to drive a 78 ohm cable. It accepts data
from the ENDEC and transmits it directly on the
DO+/DO- pins. After transmission has started,
the CS8920A expects to see the packet "looped-
back" (or echoed) to the receiver, causing the
Carrier Sense signal to be asserted. This Carrier
Sense presence indicates that the transmit signal
is getting through to the transceiver. If the Car-
rier Sense signal remains de-asserted throughout
the transmission, or if the Carrier Sense signal is
de-asserted before the end of the transmission,
there is a Loss-of-Carrier error and the Loss-of-
CRS bit (Register 8, TxEvent, Bit 6) is set.
AUI Receiver
The AUI receiver is a differential pair circuit that
connects directly to the DI+/DI- pins. It is de-
signed to distinguish between transient noise
pulses and incoming Ethernet packets. Incoming
packets with proper amplitude and pulse width
are passed on to the ENDEC section, while un-
wanted noise is rejected.
CI+
CI- - +
AUI
Collision
Detect
DI+
DI-
-+
DO+
DO-
Figure 3.12. AUI
AUICol (to MAC)
AUIRX
AUISQL ENDEC
AUITX
Collision Detection
The AUI collision circuit is a differential pair re-
ceiver that detects the presence of collision
signals on the CI+/CI- pins. The collision signal
is generated by an external Ethernet transceiver
whenever a collision is detected on the Ethernet
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