Freescale Semiconductor, Inc.
MC68HC05BD7 Rev. 2.0
GENERAL RELEASE SPECIFICATION
1.2
Signal Description
1.2.1
VDD and VSS
VDD is the positive supply pin and VSS is the ground pin.
1.2.2 IRQ/VPP
This pin has two functions. While in user mode, this pin serves as IRQ, a general purpose
interrupt input which is software programmable for two choices of interrupt triggering
sensitivity. These options are: 1) negative edge-sensitive triggering only, or 2) both
negative edge-sensitive and level-sensitive triggering. In the latter case, either type of input
to the IRQ pin will produce the interrupt. This interrupt can be inhibited by setting the
INHIRQ bit in the MFT register. While in bootstrap mode, this pin is used as VPP pin for
HC705 version. It is used to supply high voltage needed for programming the user EPROM.
1.2.3
EXTAL, XTAL
The EXTAL and XTAL pins are the connections for the on-chip oscillator. The EXTAL, and
XTAL pins can accept the following sets of components:
1. A crystal as shown in Figure 1-4(a)
2. An external clock signal as shown in Figure 1-4(b)
The frequency, fOSC, of the oscillator or external clock source is divided by two to produce
the internal operating frequency, fOP.
1.2.3.1
Crystal Oscillator
The circuit in shows Figure 1-4(a) 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. An internal start-up resistor of approximately 2 MΩ is provided between
EXTAL and XTAL for the crystal type oscillator.
MCU
MCU
EXTAL
XTAL
36 pF
EXTAL
XTAL
unconnected
(a) Crystal or
Ceramic Resonator
Connections
(b) External
Clock Source
Connection
36 pF
External Clock
Figure 1-4: Oscillator Connections
SECTION 1: GENERAL DESCRIPTION
Page 7
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