MC68HC705MC4 Datasheet, PDF (13/99 Pages) Motorola, Inc – Microcontrollers

MC68HC705MC4 Specification Rev. 1.5
The OSC1 and OSC2 pins can accept the following:
• A crystal as shown in Figure 1-2: Oscillator Connections(a)
• A ceramic resonator as shown in Figure 1-2: Oscillator
Connections(a)
• An external clock signal as shown in Figure 1-2: Oscillator
Connections(b)
The frequency, f_OSC, of the oscillator or external clock source is divided by two to produce
the internal bus clock operating frequency, f_OP. The oscillator cannot be turned off by
software if the Stop disable option is enabled via Mask Option.
1.3.2.1 Crystal with Internal Components
The circuit in Figure 1-2: Oscillator Connections(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 start-up. 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 start-up stabilization and to minimize output distortion.
To V_DD (or STOP)
MCU
To V_DD (or STOP)
MCU
OSC1
OSC2
OSC1
OSC2
unconnected
(a) Crystal or Ceramic^ψ
Resonator Connections
External Clock
(b) External Clock Source
Connections
ψ: Additional capacitance may be required for Ceramic Resonator option. Follow the
Ceramic Resonator manufacturer’s recommendations.
Figure 1-2: Oscillator Connections
1.3.2.2 Ceramic Resonator
In cost-sensitive applications, use a ceramic resonator in place of a crystal. Use the circuit
in Figure 1-2: Oscillator Connections(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
start-up stabilization and to minimize output distortion.
MOTOROLA
Page 4
Section 1: Introduction