ICS1893BY-10 - Release
Chapter 5 Interface Overviews
5.6 Clock Reference Interface
The REF_IN pin provides the ICS1893BY-10 Clock Reference Interface. The ICS1893BY-10 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 ICS1893BY-10 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 5.4.
Figure 5-2. Crystal or Oscillator Operation
Crystal
REF_OUT
52
REF_IN
53
25.000MHz
33 pF
33 pF
Oscillator
REF_OUT
52
REF_IN
53
NC
33 Ohm
CMOS
25.000
MHz
10 pF
ICS1893BY-10 Rev A 3/24/04
March, 2004
Copyright © 2004, Integrated Circuit Systems, Inc.
All rights reserved.
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