68HC705BD7 datasheet(17/85 Pages) FREESCALE

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SECTION 1: GENERAL DESCRIPTION

Page 7

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 M

Ω is provided between

EXTAL and XTAL for the crystal type oscillator.

Figure 1-4: Oscillator Connections

MCU

36 pF

(a) Crystal or

Ceramic Resonator

Connections

EXTAL

XTAL

36 pF

unconnected

External Clock

(b) External

Clock Source

Connection

EXTAL

XTAL

MCU

Freescale Semiconductor, Inc.

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