August 27, 1998
GENERAL RELEASE SPECIFICATION
The frequency, f
of the EPO or external clock source is divided by two to pro-
OSC
duce the internal operating frequency, f . or f
.
OP
BUS
Crystal Oscillator
The circuit in Figure 1-3(a) shows a typical oscillator circuit for an AT-cut, parallel
resonant crystal. The crystal manufacturer’s recommendations should be fol-
lowed, 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.
MCU
MCU
OSC1
OSC2
OSC1
OSC2
2MΩ
Unconnected
External Clock
(b) External Clock Source Connection
(a) Crystal or Ceramic Resonator Connections
Figure 1-3. EPO Oscillator Connections
Ceramic Resonator Oscillator
In cost-sensitive applications, a ceramic resonator can be used in place of the
crystal. The circuit in Figure 1-3(a) can be used for a ceramic resonator. The res-
onator manufacturer’s recommendations should be followed, as the resonator
parameters determine the external component values required for maximum sta-
bility and reliable starting. The load capacitance values used in the oscillator cir-
cuit design should include all stray capacitances. The ceramic resonator and
components should be mounted as close as possible to the pins for start-up stabi-
lization 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). This
configuration is possible regardless of whether the crystal/ceramic resonator or
internal VCO is enabled.
1.6.3 IRQ/V
PP
The IRQ/V input pin drives the asynchronous IRQ interrupt function of the CPU.
PP
The IRQ interrupt function has a bit to provide either only negative edge-sensitive
triggering or both negative edge-sensitive and low level-sensitive triggering. If the
MC68HC05SB7
REV 2.1
GENERAL DESCRIPTION
MOTOROLA
1-5
FREESCALE [ Freescale ]
