Freescale Semiconductor, Inc.
GENERAL RELEASE SPECIFICATION
1.4.2 OSC1 and OSC2
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The OSC1 and OSC2 pins are the control connections for the on-chip oscillator.
The OSC1 and OSC2 pins can accept the following:
1. A crystal as shown in Figure 1-3(a)
2. A ceramic resonator as shown in Figure 1-3(a)
3. An external clock signal as shown in Figure 1-3(b)
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The frequency, f , of the oscillator or external clock source is divided by two to
osc
produce the internal PH2 bus clock operating frequency, f . The oscillator cannot
be turned off by software if the stop-to-halt conversion is enabled via mask option
register 1. Refer to 8.4 Mask Option Registers (MOR).
op
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1.4.3 Crystal
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The circuit in Figure 1-3(a) shows a typical oscillator circuit for an AT-cut, parallel
resonant crystal. Follow the crystal manufacturer’s recommendations, as the
crystal parameters determine the external component values required to provide
maximum stability and reliable startup. The load capacitance values used in the
oscillator circuit design should include all stray capacitances. Mount the crystal and
components as close as possible to the pins for startup stabilization and to
minimize output distortion.
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Ceramic Resonator
In cost-sensitive applications, use a ceramic resonator instead of a crystal. Use
the circuit in Figure 1-3(a) for a ceramic resonator and follow the resonator
manufacturer’s recommendations, as the resonator parameters determine the
external component values required for maximum stability and reliable starting.
The load capacitance values used in the oscillator circuit design should include
all stray capacitances. Mount the resonator and components as close as
possible to the pins for startup stabilization and to minimize output distortion.
External Clock
An external clock from another CMOS-compatible device can be connected to
the OSC1 input, with the OSC2 input not connected, as shown in Figure 1-3(b).
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INTRODUCTION
Rev. 1.0
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