MC68HC05J3 Datasheet, PDF (20/92 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

the MCU as possible. Bypassing requirements vary, depending on how heavily the MCU pins are
2
loaded.
2.2.2
IRQ
This is an input-only pin for external interrupt sources. Interrupt triggering can be selected to be edge
sensitive or edge-and-level sensitive (see Section 1.2). The IRQ pin contains an internal Schmitt
trigger as part of its input to improve noise immunity.
2.2.3 OSC1, OSC2
These pins provide control input for an on-chip oscillator circuit. A crystal, ceramic resonator,
resistor or external clock signal connected to these pins supplies the oscillator clock. The oscillator
frequency (f_OSC) is divided by two to give the internal bus frequency (f_OP).
2.2.3.1 Crystal
The circuit shown in Figure 2-3(a) is recommended when using either a crystal or a ceramic
resonator. Figure 2-3(e) provides the recommended capacitance and feedback resistance values.
The internal oscillator is designed to interface with an AT-cut parallel-resonant quartz crystal
resonator in the frequency range specified for f_osc (see Table 9-5 and Table 9-6). Use of an
external CMOS oscillator is recommended when crystals outside the specified ranges are to be
used. The crystal and associated components should be mounted as close as possible to the input
pins to minimise output distortion and start-up stabilization time. The manufacturer of the
particular crystal being considered should be consulted for specific information.
2.2.3.2 Ceramic resonator
A ceramic resonator may be used instead of a crystal in cost sensitive applications. The circuit
shown in Figure 2-3(a) is recommended when using either a crystal or a ceramic resonator.
Figure 2-3(e) lists the recommended capacitance and feedback resistance values. The
manufacturer of the particular ceramic resonator being considered should be consulted for
specific information.
2.2.3.3 RC network
With this option, a resistor is connected to the oscillator pins as shown in Figure 2-3(c). The overall
accuracy of the RC oscillator is approximately ±25% (contact factory for more accurate details).
MOTOROLA
2-4
MODES OF OPERATION AND PIN DESCRIPTIONS
TPG
MC68HC05J3