ICS1893BF Data Sheet Rev. E - Release
Chapter 5 Interface Overviews
5.4 Clock Reference Interface
The REF_IN pin provides the ICS1893BF Clock Reference Interface. The ICS1893BF requires a single
clock reference with a frequency of 25 MHz ±50 parts per million. This accuracy is necessary to meet the
interface requirements of the ISO/IEEE 8802-3 standard, specifically clauses 22.2.2.1 and 24.2.3.4. The
ICS1893BF supports two clock source configurations: a CMOS oscillator or a CMOS driver. The input to
REF_IN is CMOS (10% to 90% VDD), not TTL. Alternately, a 25MHz crystal may be used. The Oscillator
specifications are shown in Table 5.2.
Figure 5-2. Crystal or Oscillator Operation
Crystal
ICS1893BF
REF_OUT
46
REF_IN
47
25.000MHz
33 pF
33 pF
Oscillator
ICS1893BF
REF_OUT
46
REF_IN
47
NC
33 Ohm
CMOS
25.000
MHz
10 pF
ICS1893BF, Rev. E, 8/11/09
August, 2009
Copyright © 2009, IDT, Inc.
All rights reserved.
27
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