CS8900A
Crystal LAN™ ISA Ethernet Controller
sion, or if the Carrier Sense signal is deasserted ed by an external Ethernet transceiver whenever a
before the end of the transmission, there is a Loss- collision is detected on the Ethernet segment. (Sec-
of-Carrier error and the Loss-of-CRS bit (Register
8, TxEvent, Bit 6) is set.
tion 7.3.1.2 of ISO/IEC 8802-3, 1993, defines the
collision signal as a 10 MHz ± 15% signal with a
duty cycle no worse than 60/40). When a collision
is present, the AUI Collision circuit informs the
MAC by asserting the internal Collision signal.
3.12.2 AUI Receiver
The AUI receiver is a differential pair circuit that
connects directly to the DI+/DI- pins. It is designed
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 unwanted noise is re-
jected.
3.13 External Clock Oscillator
A 20-MHz quartz crystal or CMOS clock input is
required by the CS8900A. If a CMOS clock input
is used, it should be connected the to XTAL1 pin,
with the XTAL2 pin left open. The clock signal
should be 20 MHz ±0.01% with a duty cycle be-
tween 40% and 60%. The specifications for the
crystal are described in Section 7.7 on page 121.
3.12.3 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 generat-
CIRRUS LOGIC PRODUCT DATA SHEET
38
DS271PP3
CIRRUS [ CIRRUS LOGIC ]
