MOTOROLA
Page 10
SECTION 1: GENERAL DESCRIPTION
MC68HC05V7 Specification Rev. 1.0
1.5.7
OSC1, OSC2
The OSC1 and OSC2 pins are the connections for the on-chip oscillator. OSC1 is the input
to the oscillator inverter. The output (OSC2) will always reflect OSC1 inverted except when
the device is in STOP mode, which forces OSC2 high. The OSC1, and OSC2 pins can
accept the following sets of components:
1. A crystal as shown in Figure 1-7(a)
2. A ceramic resonator as shown in Figure 1-7(a)
3. An external clock signal as shown in Figure 1-7(b)
The frequency, f
OSC
, of the oscillator or external clock source is divided by two to produce
the internal operating frequency, f
OP
.
1.5.7.1
Crystal Oscillator
The circuit in Figure 1-7(a) shows a typical oscillator circuit for an AT-cut, parallel resonant
crystal. The crystal manufacturer’s recommendations should be followed, as the crystal
parameters determine the external component values required to provide maximum
stability and reliable start-up. The load capacitance values used in the oscillator circuit
design should include all stray capacitances. The crystal and components should be
mounted as close as possible to the pins for start-up stabilization and to minimize output
distortion and radiated emissions.
Figure 1-7: Oscillator Connections
1.5.7.2
Ceramic Resonator Oscillator
In cost-sensitive applications, a ceramic resonator can be used in place of the crystal. The
circuit in Figure 1-7(a) is for a ceramic resonator. The resonator manufacturer’s
recommendations should be followed, 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. The ceramic resonator and components should be mounted as close as
possible to the pins for start-up stabilization and to minimize output distortion and radiated
emissions.
MCU
(a) Crystal or
Ceramic Resonator
Connections
OSC1
OSC2
unconnected
External Clock
(b)External
Clock Source
Connection
OSC1
OSC2
MCU
F
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n
.