Modes of Operation and Pin Descriptions
MC68HC05E6 — Rev. 1.0
Modes of Operation and Pin Descriptions
VDD and VSS
Power is supplied to the microcontroller using these two pins. VDD is the
positive supply and VSS is ground.
It is in the nature of CMOS designs that very fast signal transitions occur
on the MCU pins. These short rise and fall times place very high
short-duration current demands on the power supply. To prevent noise
problems, special care must be taken to provide good power supply
bypassing at the MCU. Bypass capacitors should have good high
frequency characteristics and be as close to the MCU as possible.
Bypassing requirements vary, depending on how heavily the MCU pins
are loaded.
IRQ/VPP
This is an input-only pin for external interrupt sources. Interrupt triggering
can be selected to be negative edge sensitive or negative edge-and-level
sensitive by correctly configuring the IRQ bit in the LVIOPT register (see
Mask options). The IRQ pin contains an internal Schmitt trigger as part of
its input to improve noise immunity.
For the MC68HC705E6, this pin also
serves as the input pin for the EPROM programming voltage (VPP).
OSC1, OSC2
These pins provide control input for an on-chip oscillator circuit. A
crystal, ceramic resonator or external clock signal connected to these
pins supplies the oscillator clock. The oscillator frequency (fOSC) is
divided by two to give the internal bus frequency (fOP).
Crystal
The circuit shown in
Figure 5(a) is recommended when using either a
crystal or a ceramic resonator.
Figure 5(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 fOSC (see Table 23). 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.
6-pin
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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