segment. (Section 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 Col-
lision circuit informs the MAC by asserting the
internal Collision signal.
3.14 External Clock Oscillator
A 20 MHz quartz crystal or CMOS clock input
is required by the CS8920A. 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 between 40% and 60%. The specifi-
cations for the crystal are described in section
13.0 (Quartz Crystal Requirements).
CS8920A
38
DS238PP2