COM90C66 Datasheet, PDF (45/76 Pages) SMSC Corporation – ARCNET Controller/Transceiver with AT Interface and On-Chip RAM

OSCILLATOR
The COM90C66 incorporates on-board circuitry
which, in conjunction with an external parallel
resonant crystal, forms an oscillator. The
oscillator frequency may vary from 8 MHz to 20
MHz to allow for a variable data rate from 1.0
Mbps to 2.5 Mbps.
The COM90C66 crystal oscillator has been
designed to work with a parallel resonant
crystal. Only two capacitors are needed (one
from each leg of crystal to ground). The values
of the capacitors are two times the lead
capacitance of the crystal. The COM90C66
contains an internal 1 MΩ resistor. The external
crystal must have an accuracy of 0.020% or
better.
1
1
0
20MHZ
CLOCK
(FOR
REF. ONLY)
100ns
nPULSE1
100ns
nPULSE2
DIPULSE
200ns
RXIN
400ns
FIGURE 13 - DIPULSE GENERATION AND RECEIVE WAVEFORM FOR DATA OF 1-1-0
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