COM20020D Datasheet, PDF (48/72 Pages) SMSC Corporation – ULANC Revision D Universal Local Area Network Controller with 2K x 8 On-Board RAM

If an external crystal is used, two capacitors are
needed (one from each leg of the crystal to
ground). No external resistor is required, since
the COM20020D contains an internal resistor. The
crystal must have an accuracy of 0.020% or
better. The oscillation frequency range is from 10
MHz to 20 MHz.
The crystal must have an accuracy of 0.010% or
better when the internal clock multiplier is turned
on. The oscillation frequency must be 20MHz
when the internal clock multiplier is turned on.
The XTAL2 side of the crystal may be loaded with
a single 74HC-type buffer in order to generate a
clock for other devices.
The user may attach an external TTL clock, rather
than a crystal, to the XTAL1 signal. In this case, a
390Ω pull-up resistor is required on XTAL1, while
XTAL2 should be left unconnected.
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